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yet remains for our author, for though “unfortunately no but owing to the conflicting views expressed by direct evidence of torpidity has ever come under" his ignorant or interested, there is a probability of a foc own observation, the Dundee Advertiser of April, 1884, of disgust being engendered for all things electrical supplies him with another straw at which to grasp-not the lay mind. No doubt there is a good deal of true that the newspaper-writer saw it at all in that light, for this statement ; on the other hand, those who take te he called the bird in question a “wanderer," which term |

interest in this all-important subject will soon led is innocently repeated by Mr. Dixon, apparently uncon

enough to be able to discern that which is impor scious that thereby he gives up his case, and drown he and worth knowing. The volume under notice has been must unless some one throws him a life-belt. Meanwhile

written in order to fill this want in electrical litering that of the "hibernating” bird is as desperate. Deprived and to teach the consumer of electrical energy some by the brutal sceptic of its ancient refuge in the depths

of the source of the light and power he is using. of Lapland lakes, or in the crumbling banks of Persian | It is admittedly a difficult task to make a techna rivers, in the mud walls of Orkney or in Irish dung-heaps, 1 subject clear to untechnical, though interested, read or even in nests of its own building in sea-girt Schleswig

| and in this case all the more so, on account of the entre Holstein, the fin de siècle Swallow desirous of enjoying technicalities of electricity as applied to everyd torpidity has to betake itself to the security of the Bell requirements. Rock Lighthouse, and even there to excite no particular

The author begins at the very beginning, and in Cup astonishment on the part of the honest men who wel

ters I. and II. deals with the lighting of rooms with all comed it. If they had looked upon it as the spirit of

oil, and electricity, naturally pointing out how very sa Robert Stevenson, or that Abbot of Aberbrothock whose the atmosphere is vitiated by the two former illuminans, memory was blessed by mediæval mariners, there would besides the damage done to paintings, book-bindings, have been some excuse for them, but they simply regarded

When discussing “ How shall I light my house bet this Swallow as the proverbial one that doesn't make a

the author treats of the efficiency and cost of the diffzza summer-it was the 12th of March. They will, we think, illuminants, and points out that although the elex learn with surprise from Mr. Dixon that “this bird may light may be the more expensive, yet the cost per la probably have spent the winter, dormant, near the light | per hour may be fairly compared with oil or gas, beurt house," while he considers “that we here have the most

these illuminants are seldom turned completely out what trustworthy evidence of a positive kind.” If this does not

a room is temporarily empty, whereas the facility indicate hibernation capabilities amongst certain birds, | switching on and off an electric lamp must naturally : pray to what else can it be attributed ?” (p. 16). We

the current and effect economy, leave our readers to answer this question as they please,

Chapter III. consists of a short description of some si but we fear their answer will not please him. They may,

the systems on which electric light is produced and sa however, like to know how the incident was recorded in

plied. Great diversity of opinion exists as to whichu the Migration Committee's schedule by the matter-of-fact

the best system on which electric energy should be safe observer :-“1884, March 12th. One Swallow (Swift)

plied for public use. In London two systems are in vogue 4 p.m. [Wind] S.E., strong B[reeze] [Weather] cloudy.

viz., The high pressure alternating current in conjunction Arrived much exhausted.” No more and no less.

with transformers, and the low pressure continuous Returning to the position whence we started we must

current system. From the consumer's point of view, s: express our deliberate conclusion that Mr. Dixon, author

long as the high pressure current is not allowed to ente? of so many works as he may be, is no authority on the

the house, it matters little what are the conditions vi subject of Migration, which he has left exactly as he

distribution, provided a continuous low pressure dirt found it. In the hope he entertains that his volume may

supply or a low pressure alternating current from : form" a basis for more elaborate study and detailed

transformer station is delivered to him, except, of course research” we entirely concur. On one, and that the

where motors are in use, and then the continuous CurTCI. most wonderful part of the whole business, the faculty

is a necessity. For installations in the country, separat whereby birds are enabled to perform their extended fights

generating plant is required, and for small installations. with such punctuality and general unerringness that the

where on the average fifteen lamps of 8 c.p. are in circu. more one knows of the subject the more one is amazed

at a time, the author says that the electrical energy C22 at it, he is silent, for it would seem that there are even

be economically generated by chemical means. The bounds to his imagination, and for this we are thankful.

primary battery referred to is a modified form of Bunses,

and the cost of producing the light is stated to be one DOMESTIC ELECTRIC LIGHTING.

penny per lamp of 8 c.p. per hour. No doubt such a bal

tery takes the place of engine, dynamo, and accumulators, Domestic Electric Lighting, Treated from the Consumer's but it is purely a matter of opinion as to the trouble and

Point of View. By E. C. De Segundo, Assoc. M.Inst. skill required to look after these batteries, and, without C.E. (London: H. Alabaster, Gatehouse, and Co., taking the prime cost into account, a gas or oil engine 1892.)

driving a dynamo and charging accumulators to run THE author of this small volume is of opinion that these fifteen 8 c.p. lamps should not cost fifteen pence

1 there is at present no literature obtainable to enable per hour. A case is known where an Otto domestic gas the untechnical public to form a judgment as to the suit- engine is easily driving seven and sometimes eight 8 cp ability of applying electrical energy to meet their various lamps, and consuming 24 cubic feet of gas per hour, requirements, and he states that at present the extended at a cost of considerably under one penny per lamp, the applications of electricity are largely engrossing attention, lamps being run direct off the dynamo.

le progress of private electric lighting is simply colonies. It is a compilation of simple experiments in lishing, the gas engine being generally the motor mechanics, physics, chemistry, physiology and health, Many of these engines are run by the Dowson

and agriculture, to prepare students for what is known as

the Class D examination. Naturally, most of the experimade on the spot, thus rendering a supply of illu

ments are old ones, but here and there one may gather ting gas unnecessary.

a new idea. The portion dealing with physiology and le author treats somewhat in detail the cost of electric health has nothing to do with dissection, but consists of ing in a house, but as this largely depends on the type experiments on ventilation, drainage, food stuffs, and the endants, brackets, &c., used, the outlay naturally

like. An interesting piece of apparatus, devised by Prof. s considerably. The most serious item in the main

Bickerton for showing the action of the lungs, is described

on p. 76. All the experiments are briefly but sufficiently nce of an installation is the breakage of the lamps.

described, and many of them are illustrated. author rejoices that this monopoly of manufacture oon expire, when competition will place better lamps | Science in Arcady. By Grant Allen. (London : le market at half the present cost.

Lawrence and Bullen, 1892.) ken as a whole this little book is interesting and

This volume will fully maintain Mr. Grant Allen's repul. It will certainly help the uninitiated consumer

tation as a popular writer on science. The essays of udy intelligently the principles of electric lighting,

which it consists are written in a bright, lively style, and

may be read with pleasure even by original investigators, render his conception of necessary expenses when

for the truths with which they deal, if not new, are at Illing the light more sensible.

least presented from new points of view. Readers who do not profess to know much about any particular

branch of science will find in these papers an excellent OUR BOOK SHELF.

introduction to some of the more attractive facts and

laws of the natural world. The volume includes some sses of the Pacific Slope, including Alaska and the ljacent Islands. Part I. By Dr. Geo. Vasey, Botanist,

archæological essays, which show very effectually that an .S. Department of Agriculture. Svo, 50 plates, with

antiquary has not necessarily much resemblance to Dr. scriptions. (Washington : Government Printing

Dryasdust. fice, 1892.) botanists of the United States Department of Agri

LETTERS TO THE EDITOR. re are working very energetically, and the importance e herbarium, library, and its publications is increasing | (The Editor does not hold himself responsible for opinions exby year. The present work is part of a series of pressed by his correspondents. Neither can he undertake rations of the North American grasses, of which we to return, or to correspond with the writers of, rejected · already noticed two parts, together making one manuscripts intended for this or any other part of NATURE. ne, devoted to descriptions and figures of the char

No nolice is taken of anonymous communications. ] 'istic species of the South-Western States. The

Macculloch's Geological Map of Scotland, ent part, which will constitute half a volume, is ted to California and the Western States. Dr. Vasey

In a recent article in this journal Prof. A. H. Green writes as us in his introduction that the grasses which are

follows: un to grow on the Pacific slope of the United States,

“Macculloch seems to have projected, but never completed, a

geological map of the whole of Scotland. The materials col. iding Alaska, number not far from 200 species, which

lected by him were, however, utilized by the Highland Society arly twice as many as we get in the British Islands.

in the construction of a general map in 1832." are all specifically distinct from the grasses growing I am sure that nothing could he farther from the wish of the of the Mississippi, and also mostly distinct from the Oxford Professor than to do an injustice to the memory of one of ses of the plains and of the desert, except in that part the greatest of the pioneers in British geology, and he will there. alifornia which partakes of the desert flora. A con fore forgive my calling attention to the following ficts, which, able number of the grasses of the mountainous judging from a subsequent letter in these pages, would seem not ns of California, Oregon, and Washington reappear to be generally known. ne mountains of Idaho, Montana, and the interior During the last twenty years of his lise Dr. John Macculloch ties. The interior of California is a dry region,

was engaged on a regular survey of Scotland, and in collecting ng in the extreme south into the desert country, and

the materials for a geological map of the cuntry. In the earlier ficient in grasses, especially of those species which

part of this period Macculloch seems to have availed himself of a continuous turf. in the present publication fifty

the opportunities afforded to him as an official of ihe Board of

Ordnance to carry on his valuable geological explorations. But he most interesting species are described and

during the latter part of the period he was regularly employed ated.

by Government io complete his geological work, and was paid e descriptions are alınost wholly the work of Dr. by the Lords of the Treasury, who in the end published his r's assistant, Prof. L. H. Dewey. The illustrations map. xcellent, and are the work of various artists-F. On July 28, 1834, Macculloch addressed to “His Majesty's

r, W. R. Scholl, T. Holm, and others, and are Treasury" a series of memoirs respecting the Geological Map apanied by full dissections. The species range under of Scotland, which was then completed. In these memoirs he enera as follows :- Imperata, 1 ; Panicum, 1 ; Cen

refers to the map as being then in existence, and gives the most . 1; Phalaris, 2 ; Hierochloe, I ; Aristida, 1; Spipa,

minute directions concerning the tints to be employed by the ryzopsis, 2; Muhlenbergia, 5; Alopecurus, 7;

colourists who were to copy the map, in order that it might coritis, 6; Calamagrostis, 10; Deschampsia, 1;

respond with his original work. He also expressed his regret

that the imperfect topography of the map on which his reum, 3; Orcuttia, 2. Only two out of the fifty species

searches had to be recorded prevented the work from being as ritish, Alopecurus geniculatus and Deschampsia

accurate as he could have wished at certain points. 'osa.

J. G. B.

Owing to relays in issuing the Government publications-not to Experimental Science. By Andrew Gray.

quite without parallel in more recent times-Macculloch's

"Memoirs on the Geological Map of Scotland" did not appear ckland: Upton and Co., 1892.)

till the year following his death (1836). The date at which the hiet interest of this little book lies in the fact that first copies of the map were issued it would probably be difficult to :s a glimpse of the science teaching in one of our determine, but as to the completion of the map before July 1834, and its subsequent issue by “the Hydrographer to the King by Climbing up one of the old lateral moraines, fortas order of the Lords of the Treasury " there can be no doubt several, the glacier is seen to be encroaching laterally and whatever.

longitudinally ; it soon extends to the base of the inner mani The first Government Geological Survey undertaken in the and then climbs upwards in a similar manner as it adres British Islands was that of Dr. John Macculloch, and the work front by turning up its edges, carrying upwards a ian's that he accomplished single-handed was a very remarkable one. rocks in front, but without materially disturbing the ne Several geological maps of Scotland, differing very widely from itself. Higher up it reaches the top of this moraine, 22 that of Dr. John Macculloch, have been issued and withdrawn rises above it like a wall, having caused the loose rocks to during the last fifty years; but any one who will compare borne up to roll down into the valley between the icze the first geological map of Scotland with the latest, also outer moraine, with masses of ice broken off the edge “published with Government authority," will be interested to glacier. see hw far the work of the early pioneer in Scottish geology As far as I am able to ascertain, by creeping under their has been found to be correct in most of its essential features by the glacier slowly spreads out the bank which it had paket those who have come after him.

in front as it advances into a more even bed to travel ce John Macculloch's title to be the author of the first geological my ob: ervations were restricted to a few yards owing: map of Scotland is as indisputable as are the similar claims of contraction of the sub-glacial space between the ice to William Smith and Richard Griffiths with respect to England the floor. I was much impressed by the fact that the site and Ireland respectively.

JOHN W. JUDD. did little in exerting that force which might be expect! 16, Cumberland Road, Kew, December 6.

such a power behind, in the way of ploughing through

moving such comparatively trifling obstructions as loose the Glaciers of Val d'Herens.

moraine banks. The two glaciers of Arolla are interesting, inasmuch as one,

It is evident from the various ages of moraines that the the Arolla, is retreating, while the other, Glacier de

parts of those glaciers have fluctuated considerably darne Zigiorenove, is advancing. This has been going on for twelve

times, but the line of demarcation between these minn

tuations and the period after these lateral valley glaces i years, according to the report which appeared in NATURE (vol. xlvi. p. 386), by Dr. Forel, dealing with Alpine glaciers and

been confluent with the main Valais glacier, and were their changes.

ing backwards, is very marked. Beyond two miles de Having visited these glaciers last summer with the object of

valley from the Zigiorenove glacier no striæ from the observing the effect of their respective movements upon the

glacier could be found, but at this distance it suddenly as morainic accumulations in front, I think a brief account may be

with fresh glaciated forms; precisely the same phenomene worth recording.

noticed in the neighbouring Val d'Anniviers, as if this wa The Arolla glacier occupies the head of the valley, and is fed

limit of the more recent fluctuations. by the snow from Mont Colon and the fields of nevé extending

At the Col de Bertol. 4500 feet above Arolla, o towards Mont Brule. The Zigiorenove glacier is one mile

11,000 feet above sea level, there are no indicais further down the valley, but does not descend so low as the

glaciation, ancient or modern, above the surface of the Arolla glacier by about 300 feet. It receives its main supply

so it would appear, however much the ice level has tan from the Pigne d'Arolla, a mountain which rises immediately

low, at this dividing ridge it has always remained the same. above the glacier, and is conspicuous by its massive snow-cap.

in other words, it has been dispersed by wind or ier This glacier is not only nearer to its supply, but descends at a

ments to lower levels at a rate equal to deposition, a steeper gradient than the Arolla glacier.

snow line was low enough to allow the ice to tra This may in some measure account for the former advancing

the Val d'Herens, the higher ice streams would sie while the latter is retreating, or, more correctly speaking, melt: 1

down upon its surface, instead of descending as los ing backwards. I was informed by local guides that the Arolla



glaciers or mountain rivers, as at present. glacier has been swelling behind' for some years ; if this be

WILLIAM SHEIT correct, and the seasons remain normal, then, in a short time,

Eastbourne House, Sutton Coldfield. this glacier must advance also ; in other words, being longer or further away from its feeding ground, the extra supply has not

Ancient Ice Ages. yet had time to reach its extremity. Appearances at the end of MESSRS. BLANFORD, in their letter (NATURE, p. 10: the glaciers are in themselves quite sufficient to indi- forth by Dr. Wallace's notice of a palæozoic glacial congkat cate their respective movements; the snout of the Arolla glacier in Victoria, Australia, say :-"It has become an accepted is buried in its own debris, composed of rocks and loam borne of faith amongst most European geologists that no 104 upon or concentrated to the surface as the ice melts. This curred before the last glacial epoch." There is no doo debris is being constantly shot down grooves or water-courses the tendency of opinion has been in that direction, r** furrowed in the sloping end or side of the glacier. At the standing the evidences to the contrary brought forward bottom of these spout-like grooves conical-shaped mounts are Blanford and others. The late Sir Andrew Ramsayez ! formed, one behind another, as the ice melts backwards, result first, so far back as 1855, to suggest that the Pero ing in a moundy, zigzag arrangement constantly seen lower glomerate of Abberley and the Clent hills was an ancie down the valley, many miles away from existing glaciers, | deposit. Although this reading was accepted by sar: and can be seen also in many of the higher valleys of North philosopher and critic as Sir Chas. Lyell (* Priest Wales.

ioth ed., vol. i. p. 223), the idea has languished The advancing Zigiorenove glacier, instead of being buried in disfavour. Having devoted a considerable De debris, turns up in shell-like flanges, exposing its under surface the last twenty years to the study of glacs in its endeavour to climb over, rather than push forward, the nomena, I early this year paid my first visit to the loose rocks in front ; a part of this loose material only is pushed The best section I saw is an excavation at Abberler forward, forming a small bank, which in no place exceeded 5 may be called boulder-gravels, and, except for its prerak feet in height, up which the ice mounts with the shell-like colour, the deposit, if dropped down on the coast of 4 flanges projecting beyond ; the under part of these projections would, in general appearance and arrangement of the se being fluied into a perfectly symmetrical pattern.

be undistinguishable from many of the glacial depis In some way the projecting rocks forming the glacier bed found there. Many of the stones have flattened facs produced these convolutions, but whether by cutting, melting, general shape resemble glaciated boulders, but the or by i he ice crystals flowing round each side, I was unable to far as I could observe in the limited time at my dispa determine, but I inay state there was no appearance of cutting not very pronounced. Since then I have found a de or grinding which would necessarily leave behind the shavings | glaciated gravels on the top of the Screes, Cumb-ries' or ice particles cut out or ground off, and little or no water was feet above the sea, which on compari-on with the present as is froin melting. We had much snow for three days, brought home from Abberley enables me to mi with a total absence of sunshine ; the atmosphere at mid-day, the latter better. The volcanic rocks of the lako when making these observations, registered 38° F. Appearances of which these gravels are composed break up into very rather suggested the idea that the ice crystals were displaced in shapes, and are planed and striated in a very similar wars a similar manner to water in a rapid river when it meets with of Abberley. I also brought home from Abberley two se obstructing boulders in its bed.

of the “paste” which fills up the interstices of ibe her

ashing and riddling this clayey matter, well waterworn and during each geological period the whole of the existing land h gravel was separated from it up to about the size of a area must have been, either at once or in rapid succession, sunk and on many of these minute pebbles, with the aid of a beneath the sea in vrder to allow of its being all covered with scope of low power, beautifully-developed striæ are to be each successive formation-an amount of repeated upheaval and sometimes on more than one face. This latter fact appears depression which hardly the most extreme convul-jonist of the ve been unnoticed before. The conclusion I have come to old school would have poslulated. I cannot make the matter t Ramsay had reasonable grounds for his belief in this clearer, and trust that on further consideration Mr. Hobson will a Permian glacial deposit, and think that if he had given

admit that his objection is invalid. ALFRED R. WALLACE. details in his otherwise able paper, geologists would bly have followed him more freely. T. MELLARD READE.

The Colours of the Alkali Metals. k Corner, Blundellsands, December 5.

IN NATURE (vol. xlvii. p. 55) is a communication by Mr. G. S. Newth, entitled “Note on the Colours of the Alkali Metals."

I write to call attention to my article on “ The Colour and The Earth's Age.

Absorption-Spectra of Thin Metallic Films, and of Incandes. Dr. A. R. Wallace's “Island Life" may be regarded as cent Vapours of the Metals ; with some observations on Electrical f the best authorities on its subject, it appears desirable Vitality,” published in the American Chemical Journal (vol. xiv. ny errors in it should be pointed out, lest any of its numer- / p. 185) and reprinted in the Chemical News (vol. Ixvi, p. 163), aders should be misled.

which gives the method employed by Mr. Newih, as well as Chapter X. (2nd edition, 1892) is an estimate of the earth's ! other methods for obtaining metals in thin films. ased on the following data :-Land area of globe, In it attention is also called to the fact that the colour of the 0,000 square miles, coast line, 100,000 miles, width of film of the metal and the colour of the vapour are widely

deposits, 30 miles, hence area of shore-deposits, different. 1,000 square miles, hence rate of deposition 19 times as Mr. Newth, however, succeeded in getting a film from sodium s that of mean rate of denudation, which latter is taken to on glass, while I did not, and his success was probably due to the loot in 3000 years.

use of a higher vacuum than I employed. He also obtained a ickness of stratified rocks 177,200 feet, hence time required rubidium film. eposit 28,000,000 years. This last result is taken to be In my paper I called attention to the similarity in colour of oximately the earth's age.

the film by transmitted light and that of the incandescent vapour appears to me that Dr. Wallace's data warrant no such which is very striking in many cases. In this respect the film of usion, for, in the 28,000,000 years in question, all that rubidium as obtained by Mr. Newth follows the rule fairly well ; I have been deposited would be a thickness of 177,200 feet but the filin which he got from sodiuin is exceptional, as accord:k, over an area of only 3,000,000 square miles, whereas, ing to the analogy furnished by other metals it should be yellow. has to be accounted for is an area of 57,coo,000 square The presence of potassium, however, might cause the green (neglecting igneous rocks and sedimentary deposits be colour which he observed, by the combination of yellow and existing seas) of the same thickness. Therefore, so far purple.

Wm. L, Dudley. Dr. Wallace's data leading to 28,000,000 years as the • Vanderbilt University School of Chemistry, 's age, they actually lead to a result 19 times as great, viz.

Nashville, Tenn., December 2.
00,000 years.
A. Geikie's estimate is (NATURE, vol. xlvi., p. 322), 100

Osmotic Pressure.
D million years. Personally, I think, the method of taking
Dum thicknesses of deposits unsatisfactory, for it assuines

In an article on osmotic pressure, in NATURE (ante, p. 103), Every tormation was deposited, with its maximum thick

Mr. Rodger very truly remarks that "at present the attitude of over the whole land area of the globe. The absurdity of

the prominent upholders of the new theory [of solutions) is one upposition is obvious. The only defence of it is that it is

of indifference as to the exact mechanism of osmotic pressure. 10 make an ample allowance (of unknown amount) for re

The numerical agreement between the measurements on solud denudation. It would, perhaps, be better to ascertain

tions and those on ga-es is regarded as ample justification for ctual thickness of a great series of successive formations, say

considering dissolved substances to be in a pseudo-gaseous conle Colorado Cañon and other regions, and from such data

dition.” Such an indifference is surely to be regretted from any imate the total average thickness. This estimate, of course,

truly scientific point of view, especially as those explanations u allow nothing for repeated denudation, but would enable

which have been given of the mechanism of osmotic pressure have o form an idea of the earth's minimum age.

been based on the supposition that the dissolved substance is in BERNARD HOBSON.

a veritable and not merely pseudo-gaseous condition. There are, iens College, Manchester, December 5.

however, many reasons for supposing that while the dissolved substance may for many purposes be regarded as analogous to

a gas, it must in reality be in a very different condition, and that u glad that Mr. Hobson has formulated his difficulty as to osmotic pressure is not due to ihe bombardment of the free easurement of geological time by the comparative rates of molecules of the dissolved substance against a diaphragm through lation and deposition, because it shows that I cannot have which they cannot pass. The impenetrability of the diaphragm ned my views as clearly as I thought I had done ; yet on to certain molecules can scarcely be attributed to any other reading over pp. 217-223 of “Island Life,” I can hardly cause than that the molecules are too large to pass through the stand how he has missed the essential point of the argu- interstices of the former, and it is scarcely conceivable that the

Fortunately, there is no dispute as to the data, only as molecules of water which do pass through can be much smaller conclusions to be logically drawn from them,

than the molecules of simple salts, which do not pass through ; liobson says that I account for a deposit of 177,200 feet still less that they can be smaller than the single atoms into Ipposed thickness of all the stratified rocks) over an area which these salts are said to be dissociated. 00,000 square miles (the estimated area over which at A very simple experiment, which I mentioned some time ago ne epoch stratified rocks are being deposited) in in the Ber. d. deutsch Chem. Gesell. (24, 3639), appears to settle 2,000 years (the deduced estimate of known geological definitely against the view that osmotic pressure is due to im; and then adds: “Whereas, what has to be accounted penetrability to the dissolved substance. A solution of propyl in area of 57,000,000 square miles of the same thickness” alcohol and water was put into a porous pot and immersed in a alics). This seems to me a most amazing misconception; vessel of water ; the water passed through the pot to the soluneans that every single formation and every stratum or tion, and this, according to the usual explanation, would show er of each formation, was deposited to the same average that the pot was impermeable to the propyl alcohol. The same ess over the whole land surface of the globe (area solution was then immersed in a vessel containing propyl alco,000 square miles)! And this implies that at every suc hol, when the alcohol was found to pass through to the solution, period, from the Laurentian to the Pliocene, the con. from which we should have to draw the diametrically opposite of denudation and deposition were totally different from conclusion that the pot is impermeable to the water. The true hey are now, since at the present time it is demonstrable conclusion obviously is that the pot is impermeable, neither to e area of deposition of continental debris is only a frac- the alcohol alone, nor to the water alone, but to the solution of

the whole continental area. It implies further, that these in each other, and that the molecules composing this solution must be larger than those of either of the two substances coming of its constant action at corresponding periods in o when separate, the solution consisting of compounds or hydrates life histories of all animals of different groups, and in a close of the iwo. I showed, moreover, in the paper above re- similar manner in individuals of one and the same group 41 ferred to that the hydrate theory of solutions was quite capable a law of such a nature, if it is to be found to act universe of accounting for and explaining the fact that the dissolved sub- | amongst Metazoa, must surely have come into action at a stance may for many purposes be regarded as being in a quasi- early period in the evolution of Metazoa gaseous condition in weak solutions, and that calculations based Metagenesis is of constant if not universal occurrence on the idea of its being truly gaseous would yield very nearly cycle of life of Protozoa. A long series of generations correct results.

duced asexually is followed by a generation produced sen The hydrate theory will also, as I showed, give an explanation that is, a generation produced by the conjugation ol twor= of the fact that electrolytes will give abnormally high osmotic viduals ; this is followed again by another long series pressures, and that the magnitude of these pressures can be cal asexually produced generations, and so on. If this is so oo culated from their electric conductivity: and the explanation among unicellular organisms of the present day, it is pot based on this theory also obviates many of the objections unreasonable to suppose it was common among the proto to which the idea of dissociation into ions is open. More ancestors of the Metazoa and of the Plants. If we are to is over, the only critical experiment which, as far as I any form of Metagenesis as a universal phenomenon know, has ever been made to test the validity of Melazoa, it must be 10 the most protoznon-like stages. the dissociation hypothesis, gives an unequivocal answer development of the Metazoon that we should look. against it, and in favour of the hydrate theory. When, There is but one strict meaning to the phrase ser for instance, sulphuric acid is dissolved in excess of water, it is generation, and that is a fusion of two cells. I Metagen represented by the dissociationists as splitting up into its ions, means anything it means the alternation of a generation resis so that the solution will contain more acting units (ions and from the fusion of two cells, with one or more generations molecules) ihan the acid and water together contained before sulting from the division of cells. they were mixed : whereas, on the hydrate theory, combina This we can perhaps find in the protozoon-like stags tion will have occurred, and there will be fewer acting units Metazoan development, and in a way analogous to the alternative present. The number of acting units may be ascertained by ob. of generations among plants. serving the depression produced by the solution on some other Spermatozoon and ovum fuse and form the fertilized ove solvent, such as acetic acid (that is, by using the very method which is the true sexually produced generation. This prodess which the dissociarionists use to prove the supposed dissociation by division a vast number of cells, and if we regard these as : of substances), and when this is done it is found that the sul. number of generations then Metagenesis is obvious encept phuric acid solution contains fewer, instead of more, units than But it is no more melazoic-if I may use such a word 10 a the acid and water separately.

the whole animal resulting from the segmentation of the Even if the above were the only arguments to be urged, it is fertilized ovum, the sexually produced generation. evident that although the idea of the dissolved substance being í This generation buds off the immature ovum. This is raly gaseous and often dissociated may be a good working hypothesis the “Primitive ovum” of the entryo. I see no reason str for the directing of investigation, it can scarcely be accepted as this may not be regarded as a distinct asexually prodorn a true theory of the nature of solutions.

generation-like the formation of the spore of the plant. SPENCER PICKERING. The immature ovum divides into two cells-first Polar bode

and more mature ovum. The more mature ovui divides in.

two cells, namely, second Polar body and mature ovum. * On a Supposed Law of Metazoan Development.

does not materially affect the argument whether we should te It is difficult not to feel disappointed that Dr. Beard has gi en gard these two processes as two separate consecutive asexually only “a preliminary sketch by way of clearing the ground” produced generations, or as one asexually produced tok (NATURE, vol. xlvii. p. 79), in place of "producing the full

cellular generation. If we take the latter view, then the argument" for a law in the existence of which he has by maturation of the ovum is more analogous to the prothaila "observation and reflection” been led to believe. For it is not

stage of the life history of plants. easy to gather from his sketch how he is able to apply a universal In either case the result is the formation of the matuse otun law to so varied a series of events and phenomena such as he comparable to the oosphere of plants, mentions, and at tbe same time to point out “the analogy which The mature ovum fuses with the mature spermatozoon obtains between the suggested mode of Metazoan development, I the sexually produced generation recurs, and the cydes and the accepted fact of an alternation of generations in the life development is completed. histories of all plants above the lowest Thallophytes." For in I cannot help thinking that if Dr. Beard wishes to discover a the higher plants the alternation of generations referred to occurs law of Alternation of Generations applicable to the wbole of the with constancy as regards period of life hi-tory, and varies only Metazoa, he will find a more lavourable hunting ground amongs slightly within the limits of the same group.

those stages of development at which the several groups Dr. Beard alludes, I presume, to one form of alternation of Metazoa approximate, than amongst those stages where they generations that of sexual with asexual generation only, or are farthest apart ; and also Dr. Beard will find the analogy Metagenesis. This he asserts constitutes a general law in the

between the supposed Metazoan law and the accepted law of development of Metazoa.

the vegetable kingdom closer than he could ever hope to find In a sense this may be true enough. If, for instance, we re. it if he continues his present line of search. gard the division of each cell as a new asexual generation, then If the above theory of the cycle of Metazoan life can be corMetagenesis is a very constant phenomenon amongst Metazoa. sidered tenable, we see that both in the Higher Plants and in the In this ca-e the life history of a Metazoon consists of a sequence Metazoa there are constantly alternating "sporophyte" and of thousands of asexually produced generations alternating with "gamophyte generations, and further, we can hod evidence one sexually produced generation, which gives apparently a ) as we should expect to do, of the origin of such a universal stimulus for another run of asexual generations in which poly. phenomenon in the single celled or protozoan life, where the morphism and division of labour are exhibited in extraordinary continuance of the species may be secured in both these ways complexity and beautiful harmony.

namely, by the formation or asexually produced spores, and as But this is not at all wbat Dr. Beard means. The series of a consequence of cell fusion, i.e. conjugation instances which Dr. Beard gives, or system of "nursing " as

Ric, AssHETOS. Steenstrup termed it, is at most a series of disconnected phenomena of frequent occurrence, and not a law. Because most Metazoa possess eyes, it is not therefore a law

Oxygen for Limelight. of Metazoan development that eyes should be developed. THE employment of oxygen for limelight and other purposes Diversity in form, number, and time of appearance of eyes, has increased enormously since the commercial introduction of is sufficient to show that the law cannot exist ; so also is it in the Brin method, by which the gas is separated from atmosphene the cases of nursing to which Dr. Beard alludes, and on which air by a now well-known chemical process. The gas so obtained he bases his argument.

is practically pure, analysis showing that as now supplied by the It seems to me that no " law " of alternation of generations | Brin companies it contains on an average 95 per cent of in Metazoa can be " enunciated " unless there is evidence forth. ! oxygen, the remaining five per cent. coasisting of inert nitrogen.

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