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industrial discoveries along these lines have been very | the various accessories are in turn described more far-reaching. The success attending the investigation

fully, as well as such appliances as are usually only of various chemical reactions occurring at high

found in the best instruments.

The most important points, such as substage contemperatures has caused a marked revival in the

densers and fine adjustment construction, are treated interest taken in inorganic chemical research. This

somewhat fully. As to the choice of a microscope, has been especially noticeable on the Continent,

reference is made to the fact that in medical schools where, to a much greater extent than with us, the and elementary science laboratories, where the cheaper brilliant and rapid development of organic chemistry form of instrument is usually provided, still no inhad led to a marked neglect of this older branch of

struction is given as to its use, and that it is too

often looked on as a mere magnifying glass. This is the science.

unquestionably true, and it is much to be deprecated The technical results are hardly less important.

that, in cases where the microscope performs such Several new and flourishing industries have been an important part in the work of instruction, no firmly established, some of them supplying hitherto attention whatever is bestowed on its principles and unknown materials, which are proving themselves of use. The most interesting paragraphs in the book

are, perhaps, those in which a comparison is made great value in the arts. A still wider field of useful

between the English and Continental stand. That ness for the electric methods of heating seems now to

the form of instrument now known as the English be opening up. So far as the electrolytic and high model is generally much superior in design and contemperature applications are concerned, there has struction to the Continental stands is admitted and been no direct competition with any existing technical insisted on by the majority of those whose opinion

is of value. At no period for many years past has processes. But now that the engineer and chemist

the English microscope stand held such a high place, have become familiar with the use of the electric

and it is greatly to be hoped that those who are in furnace, there is a great tendency to extend its a position which gives them opportunities of recomemployment to work which requires temperatures | mending one form or another will recognise this. It already attainable by fuel heating if properly applied. is much to be regretted that, so far as objectives are The possibility of generating the heat just where it

concerned, the same cannot be said. Some English

makers do undoubtedly produce lenses of good quality, is required, the ease of regulation of temperature, and

but the average is not so high, and the finest objecthe accompanying economy of heat losses, are the

tives produced by Messrs. Zeiss are still unexcelled chief factors which tell in favour of electric heating by those of any other makers. In the production under these conditions. The production of carbon of substage optical appliances, this country holds, bisulphide and the rapid development of the electrical

as it has always done, a very high position, and it

is difficult to understand why the same cannot be manufacture of steel form excellent examples of what

said of objectives. All the usual microscope accesis being achieved technically in this direction; whilst

sories, as well as their method of use, are described even in the laboratory electrically heated tube and as fully as the circumstances permit. muffle furnaces are being largely employed in place of Chapters vi. and vii. are devoted to the practical those heated by gas.

optics of the microscope and its manipulation. This

is the most important section of the book, and should It is with the interesting details of such subjects

be carefully studied. Perhaps more space might have as these that M. Minet is concerned. In view of the

been devoted to this, although it is quite easy to fact that this is but the first part of his complete understand the difficulties that might arise in atwork, it is impossible to do more than point out these tempting anything like an exhaustive treatise on main divisions of the subject. The author has drawn microscopic optics, debatable as the subject still is. largely on the patent literature, and has copiously

Altogether, the book is to be commended as a

genuine attempt to treat the subject in a simpl illustrated his descriptions with excellent diagrams

straightforward manner, so that the reader for whom and with the portraits of many of the leading investi

it is primarily intended may grasp its meaning withgators in this field of work. R. S. HUTTON. out difficulty.

J. E. B. The Practical Photographer's Annual, 1905. Edited OUR BOOK SHELF.

by Rev. F. C. Lambert. Pp. xxxvi + 160.

(London: Hodder and Stoughton, 1905.) Price Elementary Microscopy. By F. Shillington Scales, Is. 6d. net. F.R.M.S. Pp. xii + 179. (London: Baillière,

THESE pages, as we are told in the preface, are Tindall and Cox, 1905.) Price 3s. net.

intended to serve no other purpose than to aid the No instrument of research has such wide application memory of the busy photographer, and if possible to in various branches of science and commerce as the

| anticipate his daily needs. microscope. It is, perhaps, scarcely too much to say An examination of the book shows that the editor that the principles underlying its construction and use has very successfully accomplished his task, and at are often disregarded by those who employ it, and the same time has not made the volume of such sometimes totally ignored. Any treatise, therefore, a bulky nature as to render its size inconvenient. It on this subject, however unpretentious, is to be cordi. L is true that more references might have been inserted ally welcomed, and the book now under notice is one but such an addition would perhaps be questionable. that should meet a pressing need. It is written for The four sections into which the book is divided beginners or for those who have used a microscope include a dictionary of practical hints, dodges, &c.; without troubling to understand it, and who conse a collection of tables, weights, measures, everyday quently have never by any chance used it at its best. formulæ, &c.; a directory of the photographic societies

The book commences with a description of various of Great Britain and Ireland; and finally, a set of simple magnifiers and a descriptive diagram showing | indices to the first twelve numbers of the present the essential parts of a microscope. These parts and l (library) series of the Practical Photographer. Each

be founacise and prace

of these sections is arranged so far as possible fractive index n conveying progressive and regressive waves alphabetically, so that ready reference is greatly the mean value of (9*+nY”)/877, or the mean value of the facilitated. We thus have a concise and practical energy density, is constant; but the mean value of dictionary which should be found of very general

(w? +Y^)/84 varies harmonically along the direction of

propagation. For a plate extending from x=o to x=h, utility.

and subjected to a normally incident beam of mean energyMurray's Handbook of Travel-Talk. Nineteenth

density I, it can easily be verified that the mean value of edition. Pp. 688. (London : Edward Stanford,

| (? +Y^)/87 within the plate is equal to 1905.) Price 3s. 6d.

I{(12 + 1)2 – (no – 1)cos 2n«(h -- x)}/{(12 + 1)? sino nkh+4n2

cos? nkh}; THAT this little pocket-book meets the requirements of travellers is shown by the fact that this is the

consequently the resultant pressure is equal to nineteenth edition that has been issued. The success 21(122 - 1)2 sinnxh/{(n2 + 1)2 sino nah +4no cosa nkh}, of such a companion depends mainly on the arrangement and scope of the material which it contains, and

| or equal to 25,1, where J. is the normal reflecting power

or equal to 2), on these points it seems difficult to suggest any

of the plate for the radiation used.

T. H. HAVELOCK. improvements. This edition is divided into fourteen

St. John's College, Cambridge, July 14. distinct but comprehensive groups of subjects, each one containing exclusively those words and phrases which naturally belong to each section. Great pains seem to have been taken to bring the information up

An Omitted Safeguard. to date, motoring, for example, having quite a large In two schemes set out in a recent issue of NATURE, one part devoted to it. The Britisher is equally helped in

dealing with the requirements of Oxford and one with either French, German, or Italian, and such a vade

the organisation of applied science in London, there mecum as is here presented should be found of great

appears a noteworthy omission.

If the weather is proverbially the first topic of conservice to everyone who crosses the Channel.

versation of Englishmen, it is surely because of the influence it has on the well-being of the community.

Yet in both the schedules referred to no provision is LETTERS TO THE EDITOR.

made for research in meteorology. It is singular how

tardy is the recognition of so important a factor in the (The Editor does not hold himself responsible for opinions national welfare. It is to meteorology that we constantly expressed by his correspondents. Neither can be undertake appeal for help. By its daily survey of rainfall it safeto return, or to correspond with the writers of, rejected guards our water supply (now a very anxious problem, manuscripts intended for this or any other part of NATURE. being outpaced by the ever-increasing demands of populaNo notice is taken of anonymous communications.] tion, sanitation, railways, or manufacturing machinery).

We turn to it for the comparison of localities and to study The Pressure of Radiation on a Clear Glass Vane. the effects of climate or fog upon health and disease, or IN NATURE, June 29, a letter from Mr. G. F. Hull

to ascertain the relations of temperature, sunshine, or rain

fall to the prosperity of the crops and fruit gardens. We appeared under the above title. In it the writer claims to

look to the readings of the barometer to protect the safety have verified experimentally that the pressure upon a

of those working underground. Meteorology takes transparent vane is equal to the difference in the density

cognisance of the force of the wind for the protection of of energy in front of and behind the vane, and reference is made to a difference of views regarding the theory of the

structures, or of storms likely to imperil the mariner on

his voyage, and by the extension of, and the improved pressure in a non-absorbing medium. In regard to the latter point, the same result is obtained

modes of, forecasting the weather is becoming each year for the particular case in question whether the beam

of greater service to all. of

Without encroaching further upon the limits of your light is considered simply as a carrier of momentum or

space, sufficient has perhaps been said to show primâ facie whether the pressure due to radiation is regarded as arising from a mechanical bodily force integrated throughout the

grounds (while so much is proposed to be devoted to

physics, geology, or botany) for the consideration of a material medium in which the radiation is being pro

possible chair in meteorology, or for in some other way pagated. Consider the latter theory for steady radiation

repairing an omission of so serious a kind in the schemes consisting of plane polarised waves of simple harmonic

lately propounded. The large amount devoted annually period 27/KC propagated along Ox (see Larmor, Phil.

to meteorology in the United States shows the appreciation Vag., vol. vii., p. 578, 1904).

of its utility to all classes of the community by so practical We have

a people as the Americans, and that the outlay is amply CY_oy. roy_ay.

recouped by the value of the services rendered by it. cat - dx' cat dx

RICHARD BENTLEY. where e is complex if the medium is absorbing. The mechanical force per unit volume is directed along

The Hydrometer as a Seismometer. Ox and is given by

IN NATURE of June 29 Mr. Bennett discusses the motion F='/. (true current)= org? I TOY 7

of a floating hydrometer when vertical motion is imparted +8thlt)

to the (rigid) vessel containing the incompressible) fluid

in which the hydrometer floats. The solution offered is Il all the interfaces are perpendicular to Ox, then y and Y that the whole system moves precisely as a rigid body are continuous throughout, whether the medium vary con would move, and this solution clearly satisfies the very tinuously or abruptly; consequently the mean value of the simple equations of motion in the problem considered. mechanical force upon any slice of the medium can be But is such motion stable? In general it is not, and I expressed as a pressure per unit area upon each surface believe that Faraday studied experimentally the “crispequal in amount to the mean value of (* +Y)/87 at the ations” of a free surface of liquid when small vertical surface. Thus for any vane suspended in free æther (or | oscillations were imparted to the containing vessel. air) the resultant mechanical force is equivalent to a This hardly affects Mr. Bennett's conclusion that a pressure per unit area equal to the difference in energy floating hydrometer is an unsatisfactory form of seismodensity in front of and behind the vane.

meter, but perhaps it may explain the positive results The apparent confusion arises from the usual statement which some observers have obtained; elastic yielding of that the mean value of g +Y? can only vary along Ox vessel or hydrometer, although conceivably an adequate in the case of an absorbing medium, but this is true only explanation, is not the only one open to us. for progressive waves. For a transparent medium of re- Cambridge.

C. V. BURTON.

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NOTES ON STONEHENGE.

either of the remaining avenues, but one large menhir

terminates one row of stones. The others may have VIII.-ON THE DARTMOOR AVENUES (Continued).

been removed. So it is probable that the alignment M Y inquiries began at Merrivale because there is a was to the north. If so, we are dealing with the

I circle associated with the avenues a little to the setting of Arcturus, warning the summer solstice south of the west end of the longest; and again nearly, sunrise in 1860 B.c. To the S. the hills are 4° 48' or quite, south of this there is a fine menhir, possibly to the N. 4° 50. used to give a north-south line. There is another men To this result some importance must be attached. hir given on the Ordnance map, azimuth N. 70° 30 E., first, because it brings us into presence of the cult of which, with hills 3° high, points out roughly the place the solstitial year, secondly, because it shows us of sunrise from the circle in May (April 29). Although that the system most in vogue in Brittany was introthis stone has been squared and initialed, I think I am duced in relation to that vear. In Brittany, as I have justified in claiming it as an ancient monument. before shown, the complicated alignments, there are There is still another, azimuth N. 83° E., giving a 11 parallel row's at Le Ménac (p. 99) (there were line from the circle almost parallel to the avenue. I hope some local achæologist will examine it, for if ancient it will tell us whether the N. avenue or the circle was built first, a point of which it is difficult to overrate the importance, as it will show the strict relationship between the astronomy of the avenues and that of the circle, and we can now, I think, deal with the astronomical use of circles after the results obtained at Stonehenge, Stenness and the Hurlers as an accepted fact. With the above approximate values the date comes out 1750 B.C., the declination of the Pleiades being N. 6° 35'.

I now pass on from Merrivale as an example of those avenues the direction of which lies somewhere in the E.-W. direction. Others which I have not seen, given by Rowe, are at Assacombe, Drizzlecombe and Trowlesworthy; to

Setelgeuse these Mr. Worth adds Harter or Har Tor (or Black Tor).

2/730BX The avenues which lie nearly N. and S. are more numerous. Rowe gives the following :-Fernworthy, Challacombe, Trowlesworthy, Stalldon Moor, Batterdon, Hook Lake, and Tristis Rock. Of these I have visited the first two, as well as one on Shovel Down not named by Rowe, and the next two I have studied on the 6-inch Ordnance map.

Fernworthy (lat. 50° 38').—Here are two avenues, one with azimuth N. 15° 45' E., hills 1° 15'. There is a sighting stone Fig. 20. — The sight-lines at the Hurlers, showing high northern azimuth; among others. From the at the X. end. We appear to be

Ordnance map. dealing with Arcturus 1610 B.C. This is about the date of the erection of the N. avenue, parallel rows at Challacombe), were set up to watch at Merrivale.

the May and August sunrises, and the solstitial alignThe second avenue has its sighting stone built into ments came afterwards. The Brittany May aligna wall at the south end. Looking south along the ments, therefore, were probably used long before avenue, the conditions are azimuth S. 8° 42' W., hills 1860 B.C., the date we have found for Challacombe. 3° 30'.

where not the sun rise, but the setting star which Both these avenues are aligned on points within, gave warning of it was observed. but not at the centre of, the circle.

It is worth while to paint out that at Challacombe, Challacombe (lat. 50° 36').—This is a case of a | as elsewhere, the priesi astronomers so located their triple avenue, probably the remains of eight iows, monuments that the nearly circumpolar stars which in a depression between two hills, Challacombe Down were so useful to them should rise over an horizon of and Warrington. There is no circle. The azimuth is some angular height. In this way the direction-lin's 23° 37' N.W. or S.E., according to direction. The would be useful for a longer period of time, for near northern end has been destroyed by an old stream the north point the change of azimuth with change in work; there is no blocking stone to the south on the declination of the star observed is very rapid. Continued from p. 248.

Shovel Down, near Batworthy (lat. 50° 39' 20').

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A group of five rows of stones, four double, one was towards the north; the height of the horizon 1 single, with two sets of azimuths.

measured as 45'. It may have been an attempt to One set gives us 229, 250, and 28°. They seem to mark the N. point of the horizon. be associated. I will call them A, B, and C. A is The triple circle to which I have referred is not an directed to the circle on Godleigh Common. Its ends ordinary circle. I believe it to be a later added, much are free. B is a single line of stones to the E. of the embellished, cairn. According to Ormerod, the triple circle, about which more presently. It is not diameters are 26, 20, and 3 feet, and there are three marked on the Ordnance map; its ends are also free. stones at the centre. C has its south end blocked, I think in later times, All the above avenues are on the slope of the hill

to the north. On the south slope we find the longest of all, as shown on the Ordnance map survey of 1885. There is a “ long stone" in its centre, and at the southern end was formerly a cromlech, the “ three boys." Part of this avenue, and two of the

three “ boys,” have been taken to Sion tras

build a wall. The long stone remains, because it is a boundary stone!

The azimuth is 2° 30 W. of north or E. of south. Looking N. from the long stone, the heigh of the horizon is 2° 30'. I think this avenue was an attempt to mark the S. point.

Trowlesworthy (lat. 50° 27' 30"). --The remains here are most interesting. This is the only monument on Dartmoor in which I have so far traced any attempt to locate the sun's place at rising either for the Mayor solstitial year. But I will deal with the V.-S. avenue first, as it is this feature which associates it with Fernworthy and Challacombe, and

in order that a comparison may be incas De

made 1 append a map showing the sight-lines at the Hurlers

(Fig. 20). FIG. 21.–The sigbt-lines at Trowlesworthy, showing high northern azimuths among others. From the Ordnance map.

As at Merrivale, the avenue has

a decided “kink" or change of by a kistvaen. The astronomical direction may be, i direction. The facts as gathered from the 6-inch map therefore, either N.W. or S.E. We find, however, a are as follows:probable use in the N.W. quadrant, as at Challa

Az. Hills Dec. Star Date combe, Arcturus setting at daybreak as a warner of

S. part of Avenue N. 7 E. 2 52 41 20 10 Arcturus 2130 B.C. the summer solstice.

N., , N. 12 E. 2 52 41 6 20

2080 B.C.

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Fig. 22.–The remains of the eight rows of the Challacombe Avenue looking North of East, terminal menhir to the extreme right.

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The height of hills is 46 ; we have then :-
N. Dec.
Star

Date
22 ... 36 19 14 ... Arcturus ... 1210 B.C.
25 ... 35 23 20 ...

... 1040 28 ... 34 19 30 ...

... 850. Adjacent to A, B, C, is another avenue, which I will call D. Unlike the others, its northern end points 2o E. of V. Its southern end is blocked by a remarkable triple circle, the end of the avenue (lose to it being defined by two tall terminal stones. We are justified, then, in thinking that its orientation

This date is very nearly that of the use of the S. circle at the Hurlers, and it is early for Dartmoor ; , but it is quite possible that local observations on an

associated avenue a little to the west of the circle which terminates the N.-S. avenue will justify it. This is not far from parallel to that at Merrivale, but its northern azimuth is greater, so that if it turns out to have been aligned on the Pleiades its date will be some time before that of Merrivale, that is, before 1680 B.C. I can say nothing more about it until I have visited it.

The new features to which I have referred are two

tumuli which in all probability represent more recent nothing more recondite than an inspection of a preadditions to the original scheme of observation, as cessional globe to have been precisely the stars, the we have found at Stenness; and show that Trowles “ morning stars," wanted by the priest-astronomers worthy was for long one of the chief centres of who wished to be prepared for the instant of sunrise worship on Dartmoor. Their azimuths are S. 64o E. at the critical points of the May or solstitial year. and S. 49° W., dealing, therefore, with the May year

NORMAN LOCKYER. sunrises in November and February and the solstitial sunset in December. It is probable that, as at the Hurlers, tumuli were used instead of stones not THE BOTANICAL CONGRESS AT VIENNA. earlier than 1900 B.C.

THE International Botanical Congress, held at Stalldon Moor (lat. 50° 27' 45") I have already 1 Vienna on June 11-18, was an impressive incidentally referred to. The azimuth of the stone demonstration of the activity of botany as a science, row as it leaves the circle, not from its centre as I and of the enthusiasm of its adherents. Vienna is read the 6-inch map, is N. 3° E.; as the azimuth not the most central town for a meeting-place, but, gradually increases for a time, we may be dealing nevertheless, more than six hundred botanists, men with Arcturus, but local observation is necessary. and women, representing nearly all the important,

The differences between the Cornish and Dartmoor and many of the less important, botanical institutions monuments give much food for thought, and it is of the world, met together there. As might have been to be hoped that they will be carefully studied by expected, the central European element predominated, future students of orientation, as so many questions but there were a goodly number of Americans reare suggested. I will refer to some of them.

presenting the southern and far western as well as (1) Are the avenues, chiefly consisting of two rows the eastern States, while from the Far East came a of stones, a reflection of the sphinx avenues of Egypt? deputation of two Chinese. and, if so, how can the intensification of them on On the first day of the Congress, members were Dartmoor be explained ?

invited to be present at the opening of the Botanical (2) Was there a double worship going on in the Exhibition, which was held in the orangery of the avenues and the circles at the same time? if not, historic Palace of Schönbrunn, just outside the town. why were the former not aligned on the circles? The exhibition was an interesting one, and gave a On a dead level, of course, if the avenues were good idea of the present position of botany from a aligned on the centre of the circle towards the rising teaching as well as from a more general point of or setting of the sun or a star, the procession in the view. I here were fine series of diagrams, and via sacra would block the view of those in the circle. coloured photographic lantern-slides of microscopic We have the avenue at Stonehenge undoubtedly preparations, flowers, plant associations, and other aligned on the centre of the circle, but there the naos objects; living cultures of Algæ; apparatus of all was on an eminence, so that the procession in the kinds; and some beautiful photographs of tropical avenue was always below the level of the horizon, , vegetation in Brazil, Malaya, and elsewhere. A reand so did not block the view.

markable feature was the unique specimen of Fockea (3) Do all the cairns and cists in the avenues re capensis, a member of the family Asclepiadaceæ, present later additions, so late, indeed, that they which, originally brought from the Cape, still remains may have been added after the avenues had ceased the only known specimen. The plant has a hard, to be used for ceremonial purposes? The cairn at woody rhizome, as big as a child's head, from which nearly the central point of the S. avenue at Merrivale in the rainy season numerous shoots are developed. was certainly not there as a part of the structure It was figured and described by Jacquin in his when the avenue was first used as a via sacra for “ Fragmenta ” at the beginning of the last century. observing the rising of the Pleiades. I have always | The Botanic Garden of Schö:ibrunn brings to mind, held that these ancient temples, and even their at any rate for the systematic botanist, the name of attendant long and chambered barrows, were for the Jacquin, and some of his manuscript and original living and not for the dead, and this view has been drawings were an important feaiure of the exhibition, strengthened by what I have observed on Dartmoor. and a subject of envious admiration of certain

There was good reason for burials after the sacred | American botanists; we in London are proud to nature of the spot had been established, and they may possess some of Jacquin's work, in the form of have taken place at any time since; the most probable botanical letters to Sir Joseph Banks's librarian, time being after 1000 B.C. up to a date as recent as | Dryander, copiously illustrated with exquisitely deliarchæologists may consider probable.

cate drawings. His herbarium, consisting largely of Mr. Worth, whose long labours on the Dartmoor | plants cultivated in the Vienna and Schönbrunn avenues give such importance to his opinions, ob gardens, was bought by Banks, and is now in the jects to the astronomical use of those avenues because general collection at the Natural History Museum there are so many of them; he informs me that he Nicolas Joseph Jacquin was professor of chemistry and knows of 50; I think this objection may be considered botany at Vienna from 1768-96; later in the week less valid if the avenues show that they were dedicated of the congress a bust was unveiled in his honour to different sacred uses at different times of the year. | in the Fest-Saale of the university. To quote from For instance, Challacombe is not a duplicate of Mer- | Prof. Wiesner's appreciation at the ceremony :-" His rivale; one is solstitial, the other deals with the May broad horizon and great powers of organisation were year, and a complete examination of them-I have shown in the fact that, in the second half of the only worked on the fringe--may show other differ eighteenth century, no scientific, and especially no ences having the same bearing.

natural scientific, undertaking was started in which In favour of the astronomical view it must be Jacquin did not take an important part. He embodied borne in mind that the results obtained in Devon and the ideal of the academic teacher." On the same Cornwall are remarkably similar, and the dates are occasion was also unveiled the bust of Jan Ingenroughly the same. Among the whole host of heaven housz (1730-99), a Netherlander by birth, who spent from which objectors urge it is free for me to select the greater part of his working life in Vienna. any star I choose, at present only six stars have been | Physician to the Empress Maria Theresa and the considered, two of which were certainly used after- | Emperor Joseph II., botanists know nim

| Emperor Joseph II., botanists know him best as one wards at Athens; and these six stars are shown by of the earliest workers in the sphere of plant

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