new face upon the cultivation in Java. The bark of some of the trees has yielded as much as 10 per cent. of quinine; and the news of this remarkable result has produced much the same effect on Cinchona planters in Ceylon and Southern India as the discovery of a gold-field on the inhabitants of an Australian city. The Java officials have however behaved with singular liberality in the matter, and in the course of a few years it cannot be doubted that Ceylon will be abundantly supplied with this valuable kind, which, there seems reason to think, may prove to be a distinct species. Part of the seed sent in the first instance to the Nilgiris seems to have found its way to Sikkim, and the Government plantations there are believed to be in possession of a strain of Calisaya, little if at all inferior to that possessed by the Dutch.

The Government of Bengal have effected an enormous saving by using, in hospitals and dispensaries, instead of quinine imported from Europe, the febrifuge manufactured at the Sikkim plantations. The Government estimated that in consequence, by the end of 1879, “the plantations will have cleared off the entire capital that has been invested in them."

And this leads us to what is really the painful feature in Mr. Markham's book. He complains in repeated and in bitter terms of the want of justice which has been shown to those whom he employed in the business of collecting. "Those who did the work have not received fair recompense for most valuable services." It is rather singular to find that he adduces in support of this statement the case of Mr. Ledger, who was not even in any way commissioned to do what he did. But the remuneration which his actual agents received was the ground of no complaint on their part, and was in point of fact liberal compared with that which is given to the collectors who are constantly employed by the great nurserymen, and who too often lose their lives in their arduous pursuits without the satisfaction of feeling that they are doing so in an enterprise like this of lasting utility. But we fear that if Mr. Markham's assistants have reason to complain the blame must, on his own showing, be laid at his own door. He tells us (p. 271): "The system I adopted was . . . to include very slight remuneration in the original agreements. Thus the loss to Government would be insignificant if the work was not executed satisfactorily. If, on the other hand, the arduous tasks were successfully performed . . . I anticipated no difficulty in obtaining fitting recognition for such distinguished services." We leave our readers to judge of the probability of such a scheme answering Mr. Markham's expectations. We may go further, and ask how the claims would have stood if, notwithstanding all the pains that were taken, the cultivation of Cinchonas had fared in India as might even have happened—no better than it at first did in Java.

But there are many other things pleasanter than this which we should like to touch upon if this review had not already run to an inordinate length. So many Englishmen are now in one way or other interested in colonial industries that it will be strange if this interesting book does not find as many readers as it deserves. Besides a complete history of the Cinchona enterprise in the Old World, it gives, in an appendix, accounts of some other South American vegetable products, notably india-rubber.

The steps taken at Mr. Markham's instance for the introduction into India of the most important rubberyielding plants of the New World have been from time to time recorded in our pages. We have only to repair one inadvertent omission on Mr. Markham's part, and point out that the transmission of the Para rubber plant to India was secured by the exertions of Mr. Wickham, as recorded in the Kew Report for 1876, p. 8.

PRACTICAL BLOWPIPE ASSAYING

Practical Blowpipe Assaying. By George Attwood. With Seventy-four Woodcuts. (London: Sampson Low, Marston, Searle, and Rivington, 1880.)

THIS

HIS book shows many signs of carelessness on the part of the author. At the very outset, in the Introduction, we meet with strange statements. Mr. Attwood divides the elements into those which are of commercial value and those which are of no commercial value. In the latter class we find Uranium and Tungsten; surely the author does not intend to deny the value of pitchblende and wolfram. He classifies zirconium among the non-metallic elements.

The first part of the work describes the reagents and apparatus; the second, we are told, contains the modes of determining any one of the sixty-four well-recognised elements, and in the third part we have the methods adopted by the author for making quantitative assays by the blowpipe. Finally, Part IV. contains some tables showing the English and American values of gold according to its fineness, and the value of gold coins in the United States.

The apparatus employed is much the same as that recommended by Plattner. Like Neumann, Mr. Attwood very wisely uses riders with his balance instead of the very small weights supplied by some of the other Freiberg opticians; but the balance would be improved by the addition of a movable arm for shifting these riders. The steelyard devised by the author will probably be of use to explorers. From practical experience with the batea I can fully endorse all that is said in its favour, but why are the merits of the iron pan ignored? It has the advantage that it will stand rougher usage than the batea. Again, for washing a sample of tin ore nothing will beat the Cornish vanning shovel.

I regret to see no mention of the useful little pastilles and crucibles made out of charcoal powder, proposed by Griffin thirty or forty years ago and adopted by Plattner. Col. Ross's aluminium plate for sublimates seems also to have escaped Mr. Attwood's notice.

With reference to the list of reagents I must remark that the author does not name all the reagents which his tests require, whilst others are inserted which he does not appear to put to any use. I should be glad to know what he means by inserting "nitrous acid" among his reagents. This is not a misprint for "nitric acid," because that acid has been already named.

The plan of the second part of the work is not one which I should recommend. It simply contains a list of tests for the various elements, but gives no systematic scheme for making the examination of an unknown substance. I fear that the "direct" method advocated by Mr. Attwood will often prove a very tedious one. Many of the tests themselves are not so complete as they

shows the various causes in operation at the time to instigate such voyages, causes mainly political and commercial. Other influences were however at work, not the least of which was "the total transformation

which astronomy and geography had undergone" during the sixteenth century. The narratives here given are those of Hawkins's and Frobisher's three voyages, Drake's voyages of 1577 and 1585, Gilbert's voyage of 1583, Amadas and Barlow's voyage, 1584; Cavendish's first and last voyages, and Raleigh's voyage to Guiana. Prefixed to each narrative is a short historical introduction.

LETTERS TO THE EDITOR

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts. No notice is taken of anonymous communications. The Editor urgently requests correspondents to keep their letters as short as possible. The pressure on his space is so great that it is impossible otherwise to ensure the appearance even of communications containing interesting and novel facts.]

Black Sheep

THE following extract of a letter from Mr. Sanderson of Chislehurst, who permits me to publish it, seems worth placing on record. It relates to the former frequent appearance of spetted or black sheep in the Australian flocks, as long as animals thus coloured were of use to man, although they were never, as far as Mr. Sanderson knows, separately bred from, and certainly not in his own case. On the other hand, as soon as coloured sheep ceased to be of use they were no longer allowed to grow up, and their numbers rapidly decreased. I have elsewhere assigned reasons for the belief that the occasional appearance of dark-coloured or piebald sheep is due to reversion to the primeval colouring of the species. This tendency to reversion appears to be most difficult quite to eradicate, and quickly to gain in strength if there is no selection. Mr. Sanderson writes:-" In the early days before fences were erected and when shepherds had charge of very large flocks (occasionally 4000 or 5000) it was important to have a few sheep easily noticed amongst the rest; and hence the value of a certain number of black or partly black sheep, so that coloured lambs were then carefully preserved. It was easy to count ten or a dozen such sheep in a flock, and when one was missing it was pretty safe to conclude that a good many had strayed with it, so that the shepherd really kept count of his fleck by counting his speckled sheep. As fences were erected the flocks were made smaller, and the necessity for having these spotted sheep passed away. Their wool also being of small value the practice soon grew of killing them off as lambs, or so young that they had small chance of breeding, and it surprised me how at the end of my sheepfarming experience of about eight years the percentage of coloured lambs produced was so much smaller than at the beginning. As the quantity of coloured wool from Australia seems to have much diminished, the above experience would appear to be general." CHARLES DARWIN

The Nature of the Chemical Elements DR. ARMSTRONG's article in NATURE, vol. xxiii. p. 141, has brought to my mind some calculations I made more than a year ago to test a theory I had long previously entertained. Most of

us who have paid much attention to the subject are agreed that the elements are capable, under exceptional circumstances, of profound chemical change. Mr. Lockyer is searching, with success as it appears, for contemporary evidence of this by examining the condition of the solar surface. The other line of evidence is historical, and turns mainly on the classification of the numerical values of chemical symbols. It is of course only

with the latter that I have to deal.

The classifications proposed by Newlands and Mendelejeff are comprehensions of much similar preceding work. They appear to me to be faulty in two ways: (1) on account of the seriously large number of elements they wholly fail to include, and (2) because of the strong stress they lay upon arithmetical series of a rough per saltum character. As I do not know of any real case of per saltum chemical change, I do not think the elements should be classified on such a basis. What is wanted is a system capable of including-with exactness and not mere approximation - the whole of the elementary num

bers; that system to be represented in the mathematical symbols of ordinary chemical change, and therefore free from a per saltum character. I have to a great extent succeeded in finding such a system, and the results bably only one fundamental form of matter; and this, as has of testing it at many points are as follow:-1. There is probeen previously supposed, yields our ordinary elements and many others by ordinary polymerisation. 2. Almost all the elementary numbers have been tried, and, with the exception of H and CI, which are a little troublesome, they fall into order very exactly. 3. This order exhibits no discontinuity, and is similar to a case of ordinary chemical change. 4. There is clearly an upper limit to this order; in other words, elementary numbers of more than a certain magnitude appear to be impossible.

It will be

Sir B. C. Brodie's method is really a classificatory one; and I with others had been very desirous to read the Third Part of the Calculus, in which it was promised ampler play. a matter for much regret if his premature death should have prevented this. But what he did publish was sound and sure: the first real symbols chemistry has yet enjoyed, and the only ones hitherto proposed whereby the process and the results of chemical change admit of unitary as well as kinetical representation. EDMUND J. MILLS

Smokeless London

As I hope soon to have an opportunity of reading a paper on this subject before a scientific audience I need not occupy your valuable space by replying to your correspondents of last week in detail. I may say however that the scheme has been carried out in practice at a gas-work to which I shall afterwards refer. When it was found that the apparatus for making gas on an extraction of six hours was insufficient for supplying the wants of the long winter evenings the distillation was stopped when gas had been removed to the extent of 5000 cubic feet per ton. The larger quantities obtained from the coal per unit of time and the superior illuminating power obtained per unit of volume tided over the difficulty and rendered the existing plant sufficient. No practical obstacles were discovered in discharging the retorts. I do not think the difference between an extraction of 5000 and 3333 cubic feet per ton would make a material change in this respect. Mr. Mattieu Williams points out a much more serious obstruction in the plethoric indifference of the gas companies. In reply to E. R. F. I may say that the fuel resulting from a uniform extraction of 3333 cubic feet per ton is practically smokeless if it is taken hot from the retorts and immediately quenched with water. Westminster, December 27 W. D. SCOTT-MONCRIEFF

Colliery Explosions and Coal-Dust ACCEPTING Mr. Galloway's view that in many mines the extent and destructiveness of colliery explosions are due to the distribution of coal-dust in the air, may I suggest the possibility of preventing the explosion from spreading beyond the sphere of the fire-damp by sprinkling the floors throughout, at certain regular intervals, with mineral oil? A shady road, with one such sprinkling, may be kept free from dust for several weeks during the summer, and the corridors of a mine, not being open to wind and rain, would of course remain wet for a longer period. A saucer filled with dust and treated with mineral oil will retain the oil for months even when exposed to sun and rain. The mixture of coal dust and oil is quite uninflammable. The experiment may perhaps be worth trying in one of the drier coal-mines. December 27 R. RUSSELL

Geological Climates

PROF. DUNCAN is under the impression that the claim of Araucaria Cunninghami to have flourished at Bournemouth during the Eocene, rests on "a bit of a leafy part of a tree, and that this bit is "squashed." The foliage is however abundant there, occurring almost wherever vegetable remains are found, from the east of Bournemouth Pier to half a mile beyond Boscombe. In one place, where a bluff is literally full of it, the di-articulated branchlets are perfect, and not in the least degree compressed. Again, the determination was not made by Prof. Haughton, but rests upon my statement that this foliage and that of A. Cunninghami cannot be distinguished one from the other. That it is Araucarian foliage I am perfectly satisfied; but whether the existing Australian species is identical and unmodified, must remain doubtful until other

organs besides foliage are found, it being by no means absolutely certain that because the foliage is identical the species are so. The discussion raised by Prof. Haughton, and continued by Prof. Duncan and Mr. Wallace, seems therefore hardly worth prolonging, since it is based upon an assumption that is only probably correct. But even if the identity were proved, a single species is not satisfactory evidence of former temperature.

I am indebted to Mr. Winslow Jones for the only information that I have yet obtained about the growth of either species in England. He recollects a small tree of A. excelsa, growing near the water's edge in a garden on the upper portion of Falmouth Harbour, which he believes died three years ago. He has seen flourishing trees at Naples, Cintra, Malta, and Algiers, but even Northern Italy seems beyond the range of successful cultivation. Of the two A. Cunninghami seems the more tender, though possibly its le s symmetric growth may have excluded it from many gardens. In Madeira it grows generally best close to the sea and in sheltered places.

Lindley was mistaken in regarding the two species as one. All the needle-leaved (Eutacta) section of Araucaria are certainly closely allied, for the species, however distinct in other respects, possess two kinds of foliage, that of the young plants being identical in all : yet otherwise the species are clearly and distinctly marked off from each other.

It

With further regard to the identification of the Bournemouth foliage with Araucaria, I find that Massalongo1 gives an excellent photograph of the same foliage from Chiavon, in North Italy, and of an immature cone consisting of 250 scales. Although existing Sequoias have cones with from 16 to 20 scales, Schimper says: "Il est sans aucun doute un Sequoia et peut-être identique au S. Sternbergii. Les cônes ont la plus grande ressemblance avec ceux du S. gigantea" (Pal. Végétale," vol. iii. p. 573). I am beginning to lose all faith in the so-called science of palæo-botany as worked out by our Teutonic brethren. Not only is the above quotation an absurdity, for which Heer is responsible, but I fail to see any good evidence to support the change made by Heer from Araucaria Sternbergii to Sequoia Sternbergii. The foliage is more Araucaria like than Sequoia-like, and has been found associated with an Araucaria cone, but never with any Sequoia cones. has nothing to do with the Icelandic foliage, neither with the Upper Miocene foliage from Turin, nor that from Bilin nor Oeningen. The true Araucaria Sternbergii characterises a wellmarked horizon, that of the Newer Eocene or Oligocene in Central Europe, and has been found at Barton in Hampshire; it differs from the Middle Eocene form (A. venetus, Mass.) of England and Italy in the needle-like leaves hugging more closely to the branchlet, as the latter differs in its turn from the Araucaria of the Grès du Soissonnais, which has needles very widely opened out. This progressive change may have taken place pari passu with the changing climate. At Sheppey, where foliage is plentiful, I have met with a beautifully-preserved axis of an Araucaria cone with the basal scales attached, exactly as we find them in the existing species.

Now with regard to Mr. Wallace's letter, I pointed out in NATURE, vol. xix. p. 126, that the Tertiary fossil plants, even of the Eocene, require at most an increase in temperature of 20°, and that the land connection between Europe, Greenland, and America, which there is reason to suppose existed then, would, by shutting out Arctic currents, have produced more than the required increment. If this theory appeared for the first time in my article, however clumsily I may have worded it, and if it has been of use to Mr. Wallace, it is only fair that the fact should be acknowledged, while if it has escaped his notice he will perhaps pardon my now drawing his attention to it. At the same time the publication of the Tertiary flora of North-East Siberia, which I had not then seen, and of Saghalien, has modified the views I put forward in a manner which I trust I may shortly find time to explain. J. STARKIE GARDNER

considerable portion of both deposits; several species of Globigerina appearing to be identical in the chalk and the modern Atlantic mud; the presence of Coccoliths and Discoliths in both formations; the abundance of Sponges in both; the presence of Porifera vitrea, the nearest representative of the Ventriculites of the white chalk; the resemblance of the forms of Echinoderms; and without attempting to reconcile these with a shallow sea-deposit, he proceeds to state the case on the other side. This consists of the difference in analysis between chalk and Globigerina-ooze, the former containing more carbonate of lime and less alumina, the presence of silica in the Globi gerina-ooze being perhaps counterbalanced by the flints in the chalk. The greater proportion of alumina certainly points to different conditions, which Mr. Wallace considers to be that chalk is the very fine mud produced by the disintegration of coral-reefs, and mentions a deposit resembling chalk at Oahu in the Sandwich Islands and the deposit in several growing reefs, without however attempting to show that there is any probability that the remains found in these would bear any resemblance to the Sponges and Echinoderms of the chalk, or why we find no remains of these Cretaceous coral-reefs.

Mr. Wallace does not state in what the greater resemblance between chalk and Globigerina-ooze of shallow over deep water consists, but he looks on it as "weighty evidence."

Mr. Gwyn Jeffries, he says, finds all the Mollusca of the chalk to be shallow-water forms, many living at forty to fifty fathoms, some confined to still shallower waters, while deep-sea forms are absent. The late Dr. S. P. Woodward considered that Ammonites probably lived in water not over thirty fathoms; and these facts are as difficult to reconcile with Mr. Wallace's views that chalk was deposited in a sea of not over a few thousand feet as in a deeper sea.

The rareness of corals and absence of coralline beds of the age of the Lower or Upper Chalk is an important objection to the theory that chalk was deposited similarly to the Oahu chalk, the beds of Maestricht and Faxoe being above the chalk, and the former are not even conformable with it.

The point I think is still an open one, whether we shall accept Mr. Wallace's views that chalk was deposited in a comparatively shallow sea and not very far from land, or in a deep sea, the immense break between the chalk and Eocene beds giving ample time for very considerable alteration to have taken place in the disposition of land in the interval. I send this letter in the hope that a discussion on the point may elicit new facts bearing on the subject. S. N. CARVALHO, JUN.

8, Inverness Terrace, Kensington Gardens, W.

On Estimating the Height of Clouds by Photography and the Stereoscope

THE great practical value of meteorological science and the desirability of extending its usefulness by the collection of data relating to atmospheric current will perhaps be sufficient excuse for asking attention to anything likely to promote this end.

In studying the currents and other peculiarities of the atmosphere a method of estimating the height, motion, and character, as also the position with respect to each other, of each stratum of cloud, is a requirement of almost paramount importance, the value of the means employed being proportional to the number of particulars provided in its record, and the facility with which any set of observations can be compared to another at any future period. With such ever-changing subjects as clouds in constant motion, and having no strongly-defined marks, the use of theodolites is almost out of the question, and the sextant and mirror process for similar reasons would be a very tedious operation.

These considerations have induced me to endeavour to make use of photography and the stereoscope, the former to secure a couple of simultaneously-exposed photographs at the extremities of a base line, and the latter to observe them reproduced apparently solid for the respective distances of the points composing the picture to be measured when superimposed on a scale of distances and placed in it. The base line is thus practically reduced to the width of the eyes, and the difficulties arising from motion eliminated.

The recording apparatus consists of a base 50 or 100 feet long, constructed of wood and turning on a pivot at the centre of its length, its extremities being suitably supported by a framework of wood or other material upon which they could easily roll. The small cameras for the ends of this are each to be hinged at the back of its base to a second board having a graduated quadrant and rackwork erected from one of its sides for adjusting

the camera to any degree of altitude. These supplementary boards are then ivoted at the centre of part of a divided circle, previously inlaid in the wood at the extremities of the base line, in such a manner that a line passing through the axis of the lenses would cut the pivots. The cameras thus furnished can be adjusted with ease to any vertical or horizontal angle. These angular adjustments of the two instruments must always coincide, with the slight exception that the horizontal ones must make internal angles with the base included between them, or, in other words, the lenses of both require to be directed to a point opposite to the centre of the base line.

The cameras also require their rapid exposing shutters to be electrically connected, to ensure the pair of sensitive plates being impressed at the same instant, and each dark slide employed to have a fine wire strained at its centre from top to bottom imme diately in front of the prepared plate, and as close as possible to it without touching. The transparent lines produced in the developed negatives by these wires will constitute the zero of distance of any pair, and during the operation of reading off must be made to agree with similar ones on the scale of measurements obtained as follows::

Upon a large cardboard rule a number of squares in fine black lines, one inside the other, and each one slightly out of the centre of its predecessor to the right hand, the outside square being then divided with a line at a tenth part of its diameter to the left of its centre. This line will indicate the zero of the scale. After placing a distinguishing mark or number in the corner of every square for purposes of identification, the cardboard will be ready to be photographed and reduced at the same time to the intended size of the cloud negatives. Two transparent positives copied from this and observed when placed side by side in a suitable stereoscope with the edges representing the left-hand one of the cardboard together, will appear in that instrument with the lines composing the zero only a few inches away, and the squares as a succession of vertical planes commencing some distance from that and receding from the eye in the order of greater to less, each one representing its own distance in space.

To find the value of these distances it will be necessary to focus the two cameras upon some terrestrial objects whose distances can be measured by any of the known methods, and negatives taken. The two resulting landscapes, when placed in the stereoscope, each superimposed face to face upon its respective scale, and the fine vertical lines of the whole made to Occupy one apparent distance, an operation offering but little difficulty, every object or point of the landscape will be found to stand out in the vertical plane suited to its own distance, the relation between them being noted for the values found by measurement of the one to be marked upon the other. As a scale prepared thus would be of no value for any other angle at which the cameras might be placed, it would be most convenient to make use of two or three angles only, more being quite unnecessary, and prepare a scale for each, or one with a reference table of values for the respective angles would suffice. Again, in respect of altitudes. As the terrestrial measurements would only be absolutely accurate for those of clouds in the zenith, or of them, if it were possible, from the earth's centre in any direction, the tables of reference would have to include calculated corrections for altitude, or the graduations could be valued for the most useful degrees by experimental means.

It will be gathered from the above that the constancy of length of the base line can be ascertained, and corrected if necessary, by taking a couple of views of the same landscape for comparison with the preceding pair; slight fluctuations of length would not however be of much consequence in dealing with the comparatively coarse measurements of thick masses of cloud floating in so short a distance as the few miles of atmosphere capable of forming them consists.

To ascertain the height of clouds photograph a pair of negatives, and place these in the stereoscope with a pair of scale plates agreeing with the angle at which they were taken, and adjust as for the landscapes described above. The data required may then be read off by noting the vertical plane each stratum occupies.

Prints of these negatives should afterwards be made for the particulars of height, direction of motion of the respective layers, point of compass, wind rate, state of barometer, thermometer, and general remarks upon the weather, to be recorded upon them for comparison or circulation.

Meteorological observatories fitted with such an addition to their present splendid collection of instruments would have their

Correction of an Error in "Island Life" My friend Dr. Günther has kindly called my attention to an extraordinary error at p. 322-323 of my "Island Life," where I state that the Loch Killin Charr (Salmo Killinensis) inhabits a lake in Mayo County, Ireland; instead of a small lake in Inverness-shire, 2000 feet above the level of the sea, as given in Dr. Günther's original description in the Proceedings of the Zoological Society, 1865, p. 698. On referring to my MSS. notes for this part of my work, I find that the habitat was first correctly given, but subsequently scored out and altered to the erroneous Irish locality! Why this was done I cannot now discover; and I can only regret that I should have fallen into so palpable an error, and request such of the readers of NATURE as possess my book to make the necessary alterations. ALFRED R. WALLACE

Natural Science for Women

WILL you allow me to supplement your kindly reference to the instruction in physical science given to women in Bedford College, London, by the statements that for the last two sessions a class in biology has been conducted there by Mr. Charles Stewart of St. Thomas's Hospital Medical School. The course of study is in every sense a practical one, with special reference to the Preliminary Scientific and First B.Sc. examinations at the University of London, and the best testimonial to the excellence of the instruction in these various subjects is furnished by the remarkable success during the present year of the Bedford College pupils at the University examinations, a success not less marked in the Science than in the Arts examinations. ALFRED W. BENNETT

Movements of Leaves

A YEAR ago we had in our conservatory a healthy young plant of Acacia mollissima. It bore no flowers, but consisted of a simple axis adorned with the soft feathery leaves of its genus, which closed up at night. Our gardener however thought it would improve in appearance if it could be made to bear a few branches; and with that view he cut it back. His end was achieved a new stem shot up from the section, and graceful limbs were thrown out in turn by it. But along with this a strange result followed the fresh leaves borne by the new stem and by the branches now closed at night, while the old leaves below the section ceased to do so. These lower leaves have long since fallen off, but the upper ones kept to their habit, and at the present time all fold up at dusk save a few of the very oldest, which only partially shut, or, in one case, do not shut at all. When our plant was cut back it stood three feet high; now it stands seven: which shows that the vigour of the plant as a whole in no wise diminished by the operation. Chislehurst, December 23

DUST

M. L. ROUSE

ON DUST, FOGS, AND CLOUDS' UST, fogs, and clouds seem to have but little connection with each other, and we might think they could be better treated of under two separate and distinct heads. Yet I think we shall presently see that they are more closely related than might at first sight appear, and that dust is the germ of which fogs and clouds are the developed phenomena.

This was illustrated by an experiment in which steam was mixed with air in two large glass receivers; the one receiver was filled with common air, the other with air which had been carefully passed through a cotton-wool filter and all dust removed from it. In the unfiltered air the steam gave the usual and well-known cloudy form of condensation, while in the filtered air no cloudiness whatever appeared. The air remained supersaturated and perfectly transparent.

The difference in the behaviour of the steam in these two cases was explained by corresponding phenomena, 1 Abstract of a paper read to the Royal Society of Edinburgh, December 20, by Mr. John Aitken. Furnished to NATURE by the Council of the Society.