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It is hard at this date to write anything new on the there are large beds in the Eastern Counties. It is fairly subject of elementary geometry, and for the class ad- active, yet sustaining dressed by the author it is not desirable, but the well- : “ Thomas's phosphate powder, or basic slag-.. known facts may be treated in very diverse ways : in is composed of 15 to 25 per cent. of phosphoric acid and this case there is a novelty and freshness which must about 45 per cent. of lime. It is not very quick in action, commend the treatment of them to all intelligent students. but lasting in effect." Take this“ precise definition" of a plane: Take two points From this description one cannot get much idea of the A and B and suppose two equal spherical bubbles formed relative values of these three phosphatic manures, and about A and B as centres. Let them expand, always basic slag suffers by comparison with ground coprolite. equal to each other, until they meet, and still keep on Practical experience shows that basic slag has a much expanding. The line where the equal spherical bubbles, higher value than ground coprolite as a manure, and has, regarded as surfaces, meet, has all its points just as far moreover, an additional value as a check upon wireworm. from A as from B. As the bubbles still expand, this Again, on p. 77, the description of the fungus causing line, with all its points equidistant from A and B, itself potato disease (phytophthora infestans) is scarcely accuexpands and traces out a plane as its path through space. rate. In describing the aerial hyphæ which spring from Hence we may define the plane as the region (or surface) | the mycelium in the leaves and push their way through where a point may be, that is, equidistant from two fixed the stomata, the author says:points. . . It is evident that the plane, as thus defined, is “ These stem-growths of the fungus produce 'fruit'. reversible. . . The superiority of this definition consists in spores (DD) in cells (Oogonia), that divide (F) and its not only telling what surface the plane is, but also liberate the active agents in reproduction, tailed making clear that there actually is such a surface. Thence zoospores (6) which float in the air, and swim in our author readily derives the notion of the ray (anglicè, the moisture, dew, or rain, on potato leaves.” The straight line: a tract being a part bounded by end points). letters in parentheses refer to fig. 18, p. 79. Neither

This manner of illustration occurs repeatedly, and text nor description below fig. 18 is correct. What Mr. adds, we think, much to the interest of the book.

Wright calls oogonia are really conidia, and what he As a specimen of the mode of proof employed we take calls conidia (F in fig. 18) represent the formation of what is equivalent to part of Euc. i. 5. Data. ABC, an oospore from oogonium and antheridium. We must an isosceles triangle, AB its base, AC and BC its equal also dissent from the author's views on zoospores floating sides (here we may remark the figure is badly drawn : a in the air. similar remark applies to figures on pp. 60 and 91). Apart from these defects the primer is well worthy of Proof. Take up the triangle ABC, turn it over, and re-perusal, and will no doubt meet with success. The pracplace it in the position BCA. Then the two triangles tical part is very well done, and this is, of course, the ACB and BCA have the equal vertical angles, C and C, most essential part of the book. WALTER THORP. also the side AC = BC (why?) and BC = AC (why?);

Ornithology in relation to Agriculture and Horticulture. hence they are congruent (why?), and the 2A = 2B. In the more elaborate proofs there is a larger crop of

Edited by John Watson. 220 pp. (London: W. H. “whys," and in some cases the interrogation is answered

Allen, 1893.) by the author.

This book contains a series of papers by well-known The amount of ground covered is considerable, and

writers. The chief interest will gather around chapters yet, as we have gone through the whole of the text, it is

iii. to vii. inclusive, which treat of the common sparrow, so clearly opened up that the intelligent student, to whom

The trial of the sparrow is opened very ably by Mr. Chas. we have previously referred, should be able to master it

Whitehead (for the prosecution). He is well supported all, and successfully grapple with the well-chosen exercises

in the next chapter by Miss Eleanor A. Ormerod. These which are arranged in fitting places throughout the book.

two writers for the prosecution will have the support of " These exercises have been chosen with especial reference

the vast majority of agriculturists in England, and their not so much to their merely disciplinary as to their

arguments contrast favourably with the less practical didactic value, the author being persuaded that quite as

defence put forward in the two succeeding chapters by good exercise may be found in going somewhither as in

the Rev. F. C. Morris and the Rev. Theodore Wood walking round the square.”

Chapter VII. is written by J. H. Gurney, Jun., and from We have no hesitation in heartily commending Prof.

the result of 755 dissections he draws up a table showing Smith's introduction to teachers and pupils as an excellent

that “in England about 75 per cent. of an adult sparrow's one, and this we vouch, adapting the language of the

food is corn, chiefly barley and wheat, with a fair quan learned counsel cited by Bailie Littlejohn, nostro periculo.

tity of oats." Nobody with experience of grain-growing

in England will deny that the sparrow is a terrible pest, Primer of Horticulture. By J. Wright. (London: Mac and it is time that a movement be made not towards millan and Co., 1893.)

exterminating the troublesome bird, but towards reducing This primer contains the substance of ten lectures

its numbers to normal limits.

Chapter IX. is an interesting defence of the rook, much delivered by Mr. Wright for the Surrey County Council.

of which defence this bird merits. It is written by Besides the lectures, some sets of questions, asked after

O. V. Aplin, who also contributes a very useful chapter he lectures, are given together with the answers to hese questions.

on miscellaneous small birds. WALTER THORP. The primer is eminently practical, and is sure to prove Mery useful both to gardeners and to students. It cannot,

LETTERS TO THE EDITOR. however, be considered quite free from errors, and a areful revision would increase its value.

[The Editor does not hold himself responsible for opinions ex. Sometimes the text is rather loose.

pressed by his correspondents. Neither can he undertake On p. 54 the word pistil is used indefinitely, sometimes

to return, or to correspond with the writers of, rejected neaning the style and at others the whole gynæcium.

manuscripts intended for this or any other part of NATURE, Speaking of phosphatic manures on p. 64 the author

No notice is taken of anonymous communications. ] ays :

Vectors versus Quaternions. "Mineral superphosphate is ground coprolite treated

Having a vivid recollection of the pleasure I derived from vith sulphuric acid.

Prof. Gibbs's attacks upon the quaternionic system in the rather “Coprolite is antediluvian petrified manure, of which one-sided discussion that took place about two years ago in this

journal, I have delayed replying to the letters of Profs, MacAulay might possibly be something in them that was not atteris and Tait, from an expectation that Prof. Gibbs would have despicable. Prof. Knott has examined them, and bas made something to say. In this I have not been mistaken ; and, as some remarkable discoveries. One of them is that those vector there is a general agreement between us on the whole, I have methods in which the quaternion is not the master lead to merely to add some supplementary remarks. Prof. MacAulay formulæ of the most prodigious and alarming complexity. He relers to me as having raised the question again. I can assure

| has counted up the number of symbols in certain equations, him it has never been dropped. Apart from the one-sided dis. | Admirable critic! cussion, it has been a live question with Prof. Gibbs and myself Now, since this discovery, and Prof. Tait's remarks, are calsince about 1882, and is now more alive than ever. I cannot culated to discourage learners, I beg leave to say, distinctly and help thinking that Prof. MacAulay's letter was overhastily emphatically, that there is no foundation for the imputation. written, and feel sure that if he knew as much about the views Prof. Knott seems to have found a mare's nest of the first and methods of those to whom he appeals as he does about magnitude ; unless, indeed, he is a practical joker, and has been Quaternions, he would have written it somewhat differently, or hoaxing his venerated friend. Speaking from a personal know perhaps not have written it at all, from a conviction of the use. ledge of the quaternionic formula of mathematical physics, ani lessness of his appeal. There is no question of suicide with us ; of the corresponding formulæ in my notation and in Prol. on the contrary, quite the reverse. I am asked whether the Gibbs's, I can say definitely that there is very little to choose "spoonfeeding," as he terms it, of Mixwell, Fitzgerald, &c., between them, so far as mere length goes. Perhaps Prof. Koott is not good enough for me. Why, of course not. It is quater has been counting the symbols in a Cartesian formula, or in a nionic, and that is the real point concerned. Again, he thinks semi cartesian one, or some kind of expanded form. I do not nothing of the inscrutable negativity of the square of a vector in write for experts who delight in the most condensed symbolism, Quaternions; here, again, is the root of the evil. As regards a I do not even claim to be an expert myself. I have to make by uniformity of notation amongst antiquaternionists, I dare say that readers, and therefore frequently, of set purpose, give expanded will come in time, but the proposal is premature. We have forms rather than the most condensed. fist to get people to study the matter and think about it. I But so far as regards the brief vector formulæ, I find that the have developed my system, such as it is, quite independently of advantage is actually in my favour. I attach no importance to Prof. Gibbs. Nevertheless, I would willingly adopt his notation this, but state it merely as a fact which upsets Profs. Koott and (as I have adopted his dyadical notion of the linear operator) and Tait's conclusions. It is desirable that I should point om if I found it better. But I do not. I have been particularly the reason, otherwise the fact may not be believed. In commod careful in my notation to harmonise as closely as possible algebra there is but one kind of product of a pair of quantities, with ordinary mathematical ideas, processes, and notation; I say F and v, which is denoted by Fv. In vector algebra there do not think Gibbs has succeeded so well. But that matters are two kinds of products. One of these closely resembles the little now; the really important thing is to depose the quater usual product, whilst the other is widely different, being a vector nion from the mastersul position it has so long usurped, whereby itself. Accordingly, to harmonise with common algebra, I the diffusion of vector analysis has been so lamentably impeded. denote the scalar product by Fv. It degenerates to Fv wheo I have been, until lately, very tender and merciful towards the vectors have the same direction. Now, since the quaternionic fads, thinking it possible that Prof. Tait might quaternionists denote this function by - Spv, which is double modify his obstructive aliitude. But there is seemingly no as long, whilst + Fv becomes F SFv, it is clear that there chance of that. Whether this be so or not, I think it is prac must be an appreciable saving of space from this cause alone, tically certain that there is no chance whatever for Quaternions because the scalar product is usually the most frequently as a practical system of mathematics for the use of physicists. occurring function. How is it possible, when it is so utterly discordant with physical But there are other causes. The quaternionic ways of notions, besides being at variance with common mathematics? | specialising formulæ are sometimes both hard to read and A vector is not a quaternion ; it never was, and never will be, lengthy in execution. Look at S. UaUpS. UBUp, which I see and its square is not negative ; the supposed proofs are perfectly in Tait's book. I denote this by (o) (Bp.), or else by rotten at the core. Vector-analysis should have a purely 2121. Bipi. Tait is twice as long. But the mere shortness is no vectorial basis, and the quaternion will then, if wanted at all, important. It is distinctness that should be aimed at, and merely come in as an occasional auxiliary, as a special kind of that is also secured by departing from quaternionic wage operator. It is to Prof. Tait's devotion to his master that we Examples of shortening and clarifying by adopting my notatio should look for the reason of the little progress made in the last may be found on nearly every page of Tait's book. 20 years in spreading vector-analysis.

Consider, for example, rotations. Quaternionists, I believe, Now I have, in my turn, an appeal to make to Prof. MacAulay. rather pride themselves upon their power of representing I have been much interested in his recent R. S. paper. As rotation by means of a quaternion. Thus, b = qal. The the heart knoweth its own wickedness, he will not be surprised continued product of a quaternion 4, a vector a, and another

I say inat i seem to see in his mathematical powers the quaternion q”, produces a vector b, which is a turned round a

mise and potency" of much future valuable work of a certain axis through a certain angle. It is striking that e hard-headed kind. This being so, I think it a great pity that should turn out so; but is it not also a very clumsy way of rehe should waste his talents on such an anomaly as the quater presenting a rotation, to have to use two quaternions, one to nionic system of vector analysis. I have examined a good deal pull and the other to push, in order to turn round the vector lodged of his paper, and can find nothing quaternionic about it except between them? Is it not plainer to say b=ra, where r is the the language concerned in his symbols. On conversion to rotator? Then we shall have ac=arr'c=rar'c=&c., ifrs purely vectorial form, I find that it is greatly improved. I the reciprocal of r. Then Prof. Tait's Vgaq'lgo (-y)ol is would suggest that he give up the quaternion. If he does not represented by Vraror'b. See his treatise, p. 326, 3rd edition, like my notation, or Prof. Gibbs's, or Prof. Macfarlane's, and and note how badly the ol ) - system works out there in will invent one for himself, it will receive proper consideration in the neighbouring pages. He will greatly extend the sphere of his usefulness by the con What, then, is this rotator ? It is simply a linear operator, version. A difficulty in the way is that he has got used to like d. It is, however, of a special kind, since its conjugee quaternions. I know what it is, as I was in the quaternionic and its reciprocal are one, thus ry=I, or = rn Far te slough myself once. But I made an effort, and recovered my from me to follow Prof. Tait's example (see his letter) and is self, and have little doubt that Prof. MacAulay can do the same. pute to him an “imperfect assimilation" of the linear and

Passing to Prof. Tait's letter, it seems to be very significant. vector operator. What I should prefer to suggest is that he The quaternionic calm and peace have been disturbed. There is | admiration for the quaternionic mantle is so extreme that he confusion in the quaternionic citadel; alarms and excursions, will wear it in preference to a better-fitting and neater garner and hurling of stones and pouring of boiling water upon the | If we like we can express the rotator in terms of a quaternide, invading host. What else is the meaning of his letter, and in another way than above, though involving direct operations more especially of the concluding paragraph ? But the worm only. But I am here merely illustrating the clumsiness of the may turn; and turn the tables.

quaternionic formulæ in physical investigations, and their : It would appear that Prof. Tait, being unable to bring his naturalness, by way of emphasising my denial and disprool massive intellect to understand my vectors, or Gibbs's, or the charge made by Prof. Tait against vectorial methods. The Macfarlane's, has delegated to Prof. Knott the task of examin- | general anti-quaternionic question I have considered elsewhere ing them, apparently just upon the remote chance that there Paignton, Devon, March 24. OLIVER HEATISIDE

Severe Frost at Hongkong.

dristed, but even on the lee side the average coating of ice was The occurrence of severe frost at moderate elevations within

about 3 inches in circumference. the Tropics must be rare. It seems worth while therefore to

(10) Evergreen shrubs and trees carried on their leaves solid place on record in the columns of NATURE some portion at

coverings of ice of an inch in thickness. The great weight of least of an official report on the low temperature which (as was

ibis ice caused the branches of trees to assume a pendent form, stated in Nature last week) occurred at Hongkong between the

The strain in many cases causing the limbs to snap off with a 15th and 18th of January :

crasb. All vegetation throughout the bill regions of the Colony

was thus covered with ice, as were also most other objects. Botanic Gardens, Hongkong, February 4, 1893.

Telegraph and telephone wires from Victoria Gap upwards Sir,—The unprecedented cold weather which the region

were covered with ice of an inch in thickness, and, in about Hongkong was recently subjected to calls for some notice

addition, carried icicles as much as three inches in length as

close as they could be packed side by side. This caused many by this department. Records of experiences of meteorological

of the telephone wires to break, and the iron post at Victoria phenomena such as we have just had besides being of passing

Gap which supported them was snapped off a few inches above interest are so frequently of use in practical dealings with various subjects that for this reason opportunities to record

the ground.

(11) The windward sides of the walls of the look-out house at unusual phenomena should not be neglected. It does not, how

the Peak were from top to bottom covered with perfectly trans ever, come within the province of this department to go much further into the meteorological aspects of the subject than is

parent ice of an inch in thickness.

(12) All the hills on the mainland and Lantao island were demanded in connection with its injurious effects on vegetation.

likewise white with ice, one of the hills (3147 feet) of Lantao (2) After a period of ordinary Hongkong dry, cool weather

having what appeared to be snow for some sew hundreds of feet rain sell on January 13, and continued daily up to the 16th

down from its summit. As early as the evening of January 15 instant. In the gardens, at 300 feet above sea level, the follow

the summit of Taimoshan (about 3300 feet) on the mainland ing quantities of rain were registered with a Glaisher's rain

had assumed a whitish appearance, presumably from ice or gauge :

snow. January 14

(13) The effect of the extremely low temperature on vegeta

... 14 , 15 ... ... ... ...

tion has been disastrous.

(15) The damage in the gardens consist chiefly in the injury or » 17

destruction of leaves, but some plants are quite killed, these being

natives of much warmer regions than Hongkong. Many of the (3) On the 15th instant the temperature fell in the afternoon decorative plants which were not killed will be months before to 39° F., at 350 feet above sea level. On the 16th, at they can regain their ornamental appearance. 9 a.m., it stood at 35° On the 17th the thermometer stood (16) Every possible precaution was adopted to minimise the at 31° at 9 a.m., which was the lowest temperature observed effect of the cold. The plant-houses, which are provided with at the Gardens. During this period the sky was overcast screens merely to produce shade, were all matted in and the except for a short time about noon on the 17th, but on the roofs covered with straw. In spite of these precautions, how. morning of the 18th it was clear and the sun shone brightly ever, many plants suffered very severely. Of serns in the houses throughout the day, the temperature having risen to 43o at Polypodium Heracleum and Adiantum tetradactylon suffered 4 p.m.

most, other kinds being but little affected. (4) Unfortunately there are no official records of temperature (17) In the orchid-house, which was covered with mats and at Victoria Peak, 1818 feet above sea level, but, by such infor- straw, all our best orchids have suffered very greatly, many mation as could be obtained from private observers in the hillbeing entirely killed while others were so much injured that, district and observations made here, it seems that the tempera even if they survive, it may be some years before they regain ture must have fallen at the summit to about 25° or 24° F. their previous luxuriant state. A healthy plant, received from

(5) On the river at Canton, and between this port and that | Calcuita several years ago, of Dendrobium aggregatum, is place, low temperatures were recorded in the reports of the apparently killed, while plants of the same species growing hy bleamships Powan and Honam. They gave

its side, and also others on trees where they had no shelter, January 16 at I A.M. 23° about 28 miles below Canton.

which I collected ten years ago on the Lo-fan mountains, about

sixty miles from Cantón, have escaped unharmed. This seems , at 10 A.M. 26° about 25 miles from Hongkong.

songkong. to show the capability of the plant in adapting itself to colder , at I P.M. 25° at Canton. 18 at 10 A.M. 28° about 25 miles from Fiongkong.

| regions than it is generally found in.

om hongkong (19) The highest point of the Gardens is 320 feet above seaI am indebted to the Office of the Hongkong, Canton, and level, the lowest part 175 feet. Some plants of the same kinds Macao Steamboat Company for these returns.

which were damaged at the upper portions were uninjured at (6) On the peninsula of Kowloon the cold appears to have | the lower parts of the Gardens. jeen greater than in Hongkong ; ice was seen on pools of water (20) of exotic trees planted on the hills Albizzia Lebbek, n the roads within fifty feet of sea-level, and at the Kowloon

Aleurites triloba (candle-nut-tree) and Eugenia Jambos (the Docks ice was observed at the bottom, thirty feet below sea rose-apple-tree) had all their leaves killed at and upwards of evel, of an empty dock.

600 feet above sea level. Trees of the rose-apple at about 800 (7) In the harbour the rigging of ships was coated with ice. feet altitude have been entirely killed. (8) Since the records began in 1884 the temperature has

(21) At 600 feet altitude indigenous plants began to be ot fallen, until now, at the observatory, below 40° F. I affected, the injuries increasing with higher altitude until at emember on one occasion, I think about seventeen years about goo feet when the extreme limit of low temperature which go, ice was found at Victoria Peak, but there is no record some plants could bear was reached, and death ensued. Most rithin my experience, which extends back nearly twenty-two

of these are tropical plants of which Hongkong, Formosa, the Lars, when ice was observed below 1700 feet aliitude.

Luchu Islands in the Far East, and Sikkim and Hinialaya in (9) The continued low temperature combined with fall of rain India are the northern limits of the geographical area from om an apparently warmer stratum of air above, resulted in the which they have been recorded. Of the plants killed or injured, ormation of ice varying in quantity from a thin coating on the Ficus Harlandi, Benth., Gordonia anomala, Spreng., and pper leaves of pine trees growing at 300 feet above sea level, Garcinia oblongifolia, Champ, are known only from Hongkong. > a thick encasement of persectly transparent solid ice of 54 | Although many of our indigenous plants have not been yet iches in circumference on the blades and bents of grass at the discovered elsewhere, it is to be expected that when China is immit of Victoria Peak. The grass bents themselves, which better known they will be found over a larger area than the ere the foundation on which the ice accumulated, were not restricted one of this island. The fact of the above named ore than an eighth of an inch in diameter, yet the formation of plants having succumbed to the late frost indicates that when e was so gradual that with the enormous accumulation of ice, they are discovered elsewhere they will be found southward of hich became its own support, the bents retained their natural Hongkong. bright, or but slightly pendent position. These large accumu. (22) Considerable damage to vegetation seems to have been tions of ice were on the windward side of the hill where rain caused about Canton, where the alluvial lands are highly cultivated. The Rev. Dr. B. C. Henry, in a letter dated January 26, | observed during the greatest cold. The colony was sheltered informs me that “the destruction of vegetation about Canton | by the mainland, and only light northerly breezes were registered has been very great. The banana plantations are ruined, and till the 20th, when the wind backed to west. It veered to the bamboos have suffered. The Aleurites triloba look all east on the 21st. During the coldest days the pressure was from shrivelled up, while Begonias, Euphorbias, Crotons and scores one to two-tenths of an inch of mercury above the mean. The of others are simply destroyed.” What Dr. Henry reports in sky was overcast, but cleared on the evening of the 17th. Oring dicates severer weather at Canton than here, Aleurites triloba to radiation the extreme temperatures occurred after this epoch: leaves being shrivelled up at Canton, while they are here at 300 the lowest air-temperature 32° o about 7 a.m. on the 18th, and feet altitude uninjured, but at 600 feet they are affected, and the lowest damp-bulb tenperature 27° -7 about 2. 30 a. m. on the completely destroyed a little higher up the hill.

same day.

W. DOBERCK, Director, (23) Accompanying this report are six photographic views Hongkong Observatory, February 1. which were taken on January 16 showing the ice at various places in the Peak district. It is somewhat difficult to represent ice in photographs, as bright light has much the same effect as ice which owes its white appearance merely to reflected light,

Mr. Preece on Lightning Protection. but it will be understood that the white in these views is pro In the recent Presidential Address to the Institution of Elecduced by ice.


trical Engineers by Mr, Preece, I find the following reference Superintendent Botanical and Afforestation Department.

to myself. HON. G. T. M. O'Brien, C.M.G.,

“ Prof. Oliver Lodge has . . . endeavoured to modify ou Colonial Secretary, &c.

views as to the behaviour of lightning discharges, and as to the The importance of such facts as these in connection with geo.

form of protectors, but without much success. His views have graphical distribution can hardly be overrated. It is customary

not received general acceptance, for they are contrary to fac to compare the range of a plant with the corresponding mean

and to experience.” annual temperature. But it is obvious that the exterminating

I was quite prepared to laugh at this with the rest, but I find effect of occasional low temperature must override every other

that the general and semi-scientific public are apt to take Mr condition. An island is often the last refuge of a species not

Preece's little jokes, of which there are many towards the end found elsewhere. Such a frost as occurred in Hongkong would

of this address, as serious and authoritative statements of erase the Double Cocoa-nut in all probability from the face of

scientific fact. And it has been represented to me that unless i creation, if it occurred in the Seychelles. In any case islands are

take some notice of the above, it may be assumed that I wish not easily restocked except with littoral vegetations and the trees

silently to withdraw from an untenable position withoat ar distributed by carpophagous birds. It seems evident therefore

knowledging having made a mistake. that the geographical distribution of plants may still be influenced

Indeed, I have already been questioned by a scientific worker by causes which are catastrophic in their nature. Of this,

as to whether I accepted the above statement as in any sense although not from cold, there is already a striking illustration in

corresponding to truth. the simultaneous destruction of the entire forest vegetation

My reply is that so far was I from that attitude, that I did which at one time covered the island of Trinidad in the South

not suppose that the statement was either meant or would be Atlantic. Mr. Knight, in the account which he has given in

taken seriously. the “Cruise of the Falcon," conjectures that the cause was

The broad question of scientific fact is this :-Givea 21 more probably volcanic than a long drought.

electrostatic charge at high potential, can the potential be The wave of cold which affected · Hongkong (or at any rate

reduced to zero most quietly and safely by a good conductor of the atmospheric conditions which produced it) seems to have

by a bad one? been tolerably extended in its range. My friend, Dr. Trimen,

The old lightning-rod doctrine (or drain-pipe theory) said, by writes to me on February 6 from Ceylon :

an extravagantly good one. I say, by a reasonably bad one. Il “We are having a wonderfully fine and dry time here, with

you employ too good a conductor the mean square of currect is extraordinary cold mornings. Here at Pecadeniya we have

appallingly strong, and all manner of dangerous oscillaties been registering at 6 a.m. 53° and 54° F., the lowest ever previ.

are set up ; whereas in a bad conductor the discharge can be more ously known being a little below 60°. The middle of the day

nearly dead-beat. These oscillations have been experimentally is very hot. Hakgala has been getting frost for the first time on

and mathematically demonstrated in a great variety of ways, the record.

unexpected and distinct effects they are able to produce bare He does not give any dates ; but the two exceptional circum

been displayed, and Messrs. Whittaker have published for me stances are sufficiently near together to make it probable that

a large book about them. some common cause produced them both.

Some critics have sensibly objected that the book is too big, W. T. THISELTON.DYER. !

but I am not aware of any scientific authority who controvers: Royal Gardens, Kew, March 28.

| my position.

If Mr. Preece only means that these views regarding lightning P.S.-Since writing the above I have received from the and its dangers are not yet practically accepted by the great Colonial Office the accompanying report on the weather of British Telegraphic Department, that is, I admit, perfectly tree January from the Hongkong Observatory.-(W. T. T.-D.]

OLIVER LODGE The mean temperature was below the average from the 14th to the 24th. The coldest day (air 35° 2, damp bulb 32° 8) was the 16th. The lowest mean temperature of the damp-bulb

The Author of the Word “Eudiometer." thermometer occurred on the 17th (air 36° 2, damp bulb 30°9). For some time past I have been endeavouring to find out the Circumstances were anti-cyclonic, with probably abnormally originator of the name eudiometer, which is now applied to the slight decrease of temperature with height. Snow-storms were measuring tubes used in gas analysis, and possibly the resalt of reported from China to the north and east of the colony. From the search may be of interest to some of the readers of NATURE Macao snow was reported, but that appears to have really con Naturally my first resort was to text-books and dicuonaries, sisted of small-sized hail, which fell for four hours. Neither but although the derivation of the word is sometimes given, the snow nor bail were seen in Hongkong, but the tops of the hills name of the author is not stated. appeared to be covered by snow or hoar-frost. Water exposed I had great hopes that the third editiou of the “Encyclopedia in buckets or in pools was several mornings found covered with | Britannica," published in 1797, would contain the desired inforice about 4 inch thick, and a few hundred feet above sea-level mation, for the article "Eudiometer" must have been written sol both the grass and branches of trees, being cooled below the long after the invention of the instrument, but it merely calls temperature of the air (which did not fall below freezing-point) | "an instrument for observing the purity of the atmospheric owing to evaporation and radiation, were encased in unusually air." Descriptions of many forms of eudiometer follow. clear and transparent ice without any appearance of crystallisa The New English Dictionary gives the derivation and the tion. As far south as the Straits Seitlements the cold was felt, first quotation is “1777. De Magellan (title), Glass apparatas but in a less degree. The temperature appears not to have fallen for making mineral waters... ...with the description of some de below 70° in Singapore. At sea strong northerly breezes were Eudiometers"; another is “ 1807. Pepys. Eudiometer in Pa

Trans. xcvii. 249. Known quantities of the air to be tried, a mere logomachia. My purpose is to show that cave-animals nd of nitrous gas being mixed, were admitted...... into a afford a particular case of the general problem how to reconcile raduated tube, which he [Priestley) denominated a eudio the law of recapitulation with the theory that adaptations or neter.” This seems to point directly to Priestley as the author | degenerations are explained by the selection of congenital of the name as he certainly was the author of the process. (It variations.

J. T. CUNNINGHAM. nay be mentioned in passing that, in this paper, Pepys describes he method of calibrating eudiometers, by pouring in equal quanities of mercury from a tube closed at one end and with the The Value of the Mechanical Equivalent of Heat. mouth ground flat, against which a piece of plate glass is pressed

IN NATURE for March 16 you published a summary of In order to obtain an exact measure of the mercury.) With these directions I searched in the library of the Royal

a communication which I had the honour to make to the Society and found Magellan's book ; but he uses the name eudio.

Royal Society. My conclusion as to the value of the C.G.S. meter as if it were well known. Mr. White, the librarian, very

unit of heat was 4'1940 x 107 ergs (see Nature, p. 478), and I kindly interested himself in the matter and found in Priestley's

added the following comment : “If we express Rowland's book, "Observations on different kinds of Air,” a statement

result in terms of our thermal unit we exceed his value by I that he had received from Landriani one of his eudiometers

part in 930, and we exceed the mean value of Joule's (selected) together with a description that he asks Priestley to print, but

determinations by one part in 350, .... if we attach equal the latter excuses himself on the ground that it would not be

value to all the results published by Joule his value exceeds ours convenient for him to publish the letter at that time. Mr.

by I part in 4280." White found the title of a book by Marsilio Landriani,

I have received so many communications with regard to this

last statement, that you will perhaps permit me to answer my "Ricerche fisiche intorno alla salubrità dell'aria" (Milano,

correspondents through your columns. 1775, 8). It is not in the libraries of the Royal or of the Chemical Society, and the title does not appear in the catalogue

I thought it unnecessary in a short summary to point out of the library of the Royal Institution, but last week I found

that the value (in gravitation and Fahrenheit units) result. the book at the British Museum. On page viii. of the Intro

ing from Joule's own experiments is not the usually acduction there is a paragraph of which the following is a trans

cepted 772:55. To me it appears an extraordinary thing that lation : "The account of the discovery of nitrous air and of

772 is to this day given in the text-books when, so far back as some of its principal properties is briefly set forth, certain

1880, Rowland conclusively proved that the results obtained defects of Priestley's apparatus are removed, and there is

from Joule's experiments give a higher value (see Proceedings,

American Academy, March 1880). added a detailed description of the Eudiometer, for that is the name which I give to my little instrument, from Eudios, a Greek

In 1879 Rowland forwarded to Joule a thermometer by

Baudin, which had been directly compared with Rowland's air word signifying goodness of the air (bontà dell'aria) accompanied by the more useful precautions for its construction.”

thermometer. Joule himself then made a careful comparison There are some plates at the end of the book containing draw

of his thermometer with the Baudin one, and communicated ings of the apparatus, and one of them is marked "Eudiometro

the results to Rowland. The complete table is given on p. 39 1775." This seems to leave it without a doubt that it is to

of the paper already referred to. In addition to the correction

thus shown to be necessary, further corrections for the capacity Landriani that we owe the word. Next as to its exact meaning: by tradition we have been

for heat of the calorimeter and contents were included, and as

the results were published in Joule's lifetime, there can be little taught that the eudiometer is an apparatus for measuring the goodness of air, and this is obviously what was intended by

doubt but that these corrections received his approval. Landriani. The New English Dictionary derives it from

I give an example (from p. 44) of Rowland's corrections :€6&tos clear (weather) and uét pov; Roscoe and Schorlemmer

Joule's value (by friction of water, in 1878) ... 7727 derive it from eúdla, fine weather, and uét pov; these meanings of the Greek words are no doubt correct, and the name would

Correction for thermometer ...

... +3'2

capacity for heat seem to be more applicable to some kind of weather glass, a

latitude (Baltimore) ... ... + '9 signification which the above quotation shows could hardly have been in Landriani's mind. HERBERT MCLEOD.

vacuum .. ... ... ... - '9 Cooper's Hill, March 21.

Corrected value at Baltimore ... 776'I Blind Animals in Caves.

It is evident that Rowland did not claim for his air thermometry

an order of accuracy greater than toi°. In the appendix to Although in my previous letter I did not give evidence his paper (p. 197) he remarks that if a certain improvement (not directly supporting the proposition that blind cave-animals are then adopted by him) was made, it is probable that an accuracy born or hatched with relatively well-developed eyes, that thesis of 'oro C. could be obtained from the mean of two or three is a good deal more than a mere supposition, as Prof. Lankester observations. I believe that my own thermometers scarcely calls it. Nor did I, as Prof. Lankester asserts, proceed to state differ much more than that from the absolute scale at any point that no such fact is known or recorded. The condition of the up to 40° C.” eyes in the newly-born young of the viviparous Amblyopsis, or A study of Rowland's methods, and of the tables given in his other cave-fishes, does not appear to have been investigated, admirable paper, leads to the conclusion that it is possible that although living young were born under observation as long ago his thermometry is in error by 1 in 1000 over the range 15° to as 1844, and exhibited as spirit specimens to the Belfast Society 25°, and such an error would suffice to bring together the reof Natural History. Nor have the early stages of the European sults (both in the value of J and in the temperature coefficient of Proteus been obtained. But, on the other hand, with respect the specific heat of water) obtained by Rowland and myself. to cave crustacea, Tellkampf, the original describer of the blind The error would, however, but slightly affect the correction of Cambarus pellucidus of the mammoth cave, stated that the eyes Joule's results. were larger in the young than in the adult (A. S. Packard, If we attach arbitrary values to Joule's later experiments, the Amer. Nat. 1871), and Garman (Bull. Mus. Comp. Zool. xvii. mean of the corrected values (by Rowland's thermometer) is 1888-89) states that in very young specimens of C. setosus, the 776-75 (= 32195); and the mean of all his determinations by blind crayfish of the Missouri caves, “the eyes are more pro. various methods is 779:17,1 and we may regard the above as minent, and appear to lack but the pigment.” In another within 1 in 1000 of the value resulting from Joule's own work blind subterranean species, Troglocaris Schmidtii, occurring in on this subject. Central Europe, Dr. Gustav Joseph found and demonstrated I trust that in future our engineers and text-book writers will that the embryo in the egg was provided with eyes. (See (even if they ignore the work of later observers) do Joule the Packard, “Cave Fauna of N. America," Nat. Acad. Sci. vol. iv. justice of discarding the traditional 772, and adopt a value Mem. .).

more in harmony with the investigations of that great exThus, although it is obvious enough that further investigation perimentalist.

E. H. GRIFFITHS. of the development of cave-animals is required, it cannot be 12, Parkside, Cambridge. said that it is altogether a "hitherto unattempted embryological research.” A discussion of this kind ought not, however, to be

i In terms of a thermal unit at 15°C.



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