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 intended for this or any other part of NATURE. No notice is taken of anonymous communications.]

Electrical Notation.

THE variety of notations for electrical quantities has become a real difficulty in reading international literature. Up to the end of last century the notation of Maxwell was the standard in Great Britain, and such extensions as became necessary were grafted on it. There is no sign of its dying out among the workers, many of them of fundamental importance, who have been accustomed to employ it-in pure science at any

rate.

You direct attention (p. 541) to the conflicting recommendations produced simultaneously by two committees, each carrying authority. As the list which you reproduce on p. 545 claims to have international force, it would be interesting to speculate how many readers could guess what are the quantities proposed to be denoted by the symbols 1, f, G. e, X, Z, S, . A German equivalent for f is given as v, which is usually synonymous with n further up in the table; so that f seems to be a duplicate. Cambridge, January 15.

J. LARMOR.

The Influence of Icebergs on the Temperature of the Sea.

was

THE part of the " Report on the work carried out by the s.s. Scotia, 1913," on the above subject, referred to in NATURE of January 14, will, I fear, be a great disappointment to many after the great promise given by the new line of investigation discovered by Prof. H. T. Barnes, of Montreal University. Prof. Barnes found, by means of a very sensitive registering thermometer, that there always a rise in temperature of the sea on approaching icebergs, and part of the Scotia's work was to check this observation. The Scotia was fitted with two sensitive registering thermometers, one to be used for trawling near the surface; the other was placed in a box through which the condenser water for the engine was pumped. Unfortunately, both these instruments soon became defective owing to sea water leaking into them. The one used for surface temperatures was repaired on the voyage, but the other does not seem to have been restored to working condition. The result is that all the temperatures taken with the recording instrument are surface temperatures taken at a depth of 2 ft.

The following is the conclusion come to by the observers on the Scotia. "An inspection of the records... leads to the conclusion that the temperature of the sea near its surface does not furnish a certain method of detecting the presence of an iceberg in the regions over which the Scotia made her voyages." Now Prof. Barnes's conclusion was not arrived at from temperatures taken near the surface, but at some depth. His records of the rising temperature on approaching icebergs were made with his first ship, in which the thermometer was placed at a depth of 5 ft., but better results were obtained by his second ship, in which it was placed at a depth of 16 to 18 ft.

In justification of their conclusion that their surface temperatures ought to give results similar to the deeper ones, the observers on the Scotia seem to have accepted Prof. Barnes's explanation of the cause of the rise in temperature near the berg. Prof. Barnes

says all the water from the melting ice is carried downwards, and that this downward current is supplied by a surface current flowing towards the berg, and that this surface current, in some way not explained, retains all the solar radiation, which he says usually penetrates deeper, but is, he says, prevented by the water being in motion. If that explanation be correct, then the Scotia's observers would be quite right in supposing that the rising temperature would be more manifest at the surface than at some depth. Though the Scotia's observers accepted Prof. Barnes's explanation of the heating of the water, they do not seem to be satisfied with it, as they say: This explanation is difficult and seems complicated."

66

Prof. Barnes's explanation is founded on the supposition that all the water of the melted ice is carried downwards. Dr. Otto Pettersson, on the other hand, says that only the water of the ice melted some distance below the surface is carried downwards, while that melted near the surface flows away from the berg on the surface. In a previous letter (NATURE, January 9, 1913) I showed by two methods of experimenting that all the water of the melted ice comes to the surface. I think it is generally admitted that the salinity of the sea is, as a rule, lower in the vicinity of melting ice than at a distance from it. If so, where does the fresh water come from if not from the melted ice? Outside the rising current of diluted sea-water next the ice there is a descending radiationcooled current of sea-water drawn from a distance and flowing underneath the ice-cooled water on the surface. This downward current is accepted by Prof. Barnes and Dr. Pettersson, though Prof. Barnes does not admit the existence of the cold-surface current. Accepting the existence of these currents in the water surrounding icebergs, the following explanation was offered in NATURE (March 16, 1913) of the rising temperature observed on approaching icebergs. The surface water at a distance from a berg has a higher temperature than the water immediately underneath it. That is, outside the influence of the berg the temperature decreases with the depth, so that when the surface water is submerged by the coldsurface current, it is sunk to some depth beneath the surface, the result of this being that a thermometer sunk to a depth of, say, 16 ft. when at a distance from the berg registers a lower temperature than if placed in the surface water; but if the deeply submerged thermometer be moved into the water near the berg, it will now register a higher temperature than it did at a distance from it, because it will now be in the submerged-surface water, the temperature of which will probably have fallen to some extent in its passage under the cold-surface water. The effect of the movement of the ship towards the berg is virtually the same as raising the thermometer towards the surface when the ship is outside the influence of the berg. In the letter referred to I suggested the use of two thermometers, one near the surface, the other at some depth, and registering together, when an inversion of the temperature would indicate the approach to ice, if the explanation be correct. If this inversion of temperature really does exist, it might be detected by the ordinary tilting thermometers, one in the water near the surface, and others at depths down to three or four fathoms, as the difference that might be looked for from Prof. Barnes's thermograms amounts at times to a degree or more Centigrade, an amount easily detected by means of thermometers of that kind.

It is a great misfortune that the thermometer in the condensation water of the Scotia could not be repaired for the investigation. The depth at which

the inlet of the condensation water was placed is not stated in the report, but from the size of the vessel it could not be very deep, and the best results could scarcely be expected from it, and for the same reason it would be of no use save in fine weather, owing to the rolling of the vessel constantly changing the level from which the water was drawn. Still, under calm conditions, it might have been deep enough to touch in some cases Prof. Barnes's rising temperature.

Prof. Barnes's results are so consistent and definite that they carry conviction, and one can scarcely imagine that the observations taken when sailing towards, and from, an iceberg in many different directions, which enabled him to draw the isotherms all round the berg as given in his report and reproduced in your issue of December 12, 1912, could be the result of chance, and not of something which had a real physical existence. It is possible that the conditions there represented may be rare, as they seem to indicate that the berg and the water had travelled together for a long time. It seems probable that in many cases the distribution of the isotherms will not be so regular owing to the berg and the water moving at different rates and in different directions. One conclusion we may, however, come to from the Scotia's observations which is that the explanation of the rising temperature on approaching icebergs is not due to radiation as supposed, as the registering thermometer on the Scotia, though not as sensitive as that used by Prof. Barnes, was yet easily capable of detecting changes such as those indicated by Prof. Barnes's thermograms. It is to be hoped that the subject will be further investigated after the war is ended. JOHN AITKEN.

Ardenlea, Falkirk, January 4.

The Longevity of Seeds.

IN the note in NATURE of January 7 (p. 515) upon Mr. Shull's paper in the Plant World, referring to the longevity of seeds, it is stated that this "is a subject on which specific information is always desirable.' The following, therefore, may at least contribute suggestion.

In 1862, my father, at a cost of 4000l., caused Dowalton Loch, the largest sheet of water in Wigtownshire, to be drained. The operation attracted considerable attention at the time, owing to the subsequent exploration of a number of "crannogs," or lake dwellings of the fascine type which were laid bare. The bottom of the lake, about 200 acres in extent, was for the most part covered with deep mud and peat; but across the centre of it lay a ridge of broken rock, now a dense jungle of dog willow (Salix caprea), whereof the seeds were no doubt wind blown.

Six years ago I was clambering among these rocks, and, coming upon an open space in the thicket, found to my surprise that the ground, to the extent of nearly an acre, was thickly covered among the stones with a carpet of Pyrola minor. Nowhere, except in Norway, have I seen this pretty plant in such profusion. Now, although I have given fairly close scrutiny to the phanerogamous flora of this country, I have not found P. minor within its bounds, though for forty years I have known of a colony of it in the neighbouring county of Kirkcudbright, about five and twenty miles in a straight line from Dowalton Loch. P. rotundifolia also grows on the banks of the Cree about twenty miles distant.

No doubt P. minor once abounded in Wigtownshire, but it has disappeared under the plough, though it may linger still in the remote moorland. Dowalton Loch lies in the heart of an arable, closely cultivated district. Whence, then, did the minute seeds come

S. T. Coleridge and the Immortality of the Protozoa. THAT Weismann's aphorism regarding the "immortality" of the Protozoa had been uttered by others before him is not unknown; and Mr. Clifford Dobell in a recent paper ascribes to Ehrenberg the first expression of the idea. Ehrenberg's book was published in 1838; but Coleridge had said the same thing many years before in his "Biographia Literaria, published in 1817 and written a couple of years earlier. In a footnote to chap. iv. (on Wordsworth's Lyrical Ballads") he says: "There is a sort of minim immortal among the animalcula infusoria, which has not naturally either birth or death, absolute beginning or absolute end: for at a certain period a small point appears on its back, which deepens and lengthens till the creature divides into two, and the same process re-commences in each of the halves now become integral." No statement of the case could well be plainer or more precise than this. I wonder whether Coleridge was indeed the first to make it; or whether some one of the eighteenth-century naturalists had already drawn the inference-not, after all, a very profound one-that a creature which multiplies by simple fission "has not naturally either birth or death," and may be called "immortal."

D'ARCY W. THOMPSON.

The Cause of Streaks upon Lath-and-Plaster Walls. FOR Some time past I have been observing the streaks which occur upon lath-and-plaster walls. I have made a survey of the literature and find no adequate treatment of the phenomenon. For that reason I take the liberty of submitting to you the results of my observations in the hope that you may find them worthy of publication. The results of my observations are as follows:

(1) The striations are accumulations of dust upon the surface of the plaster. They may be wiped off

with a cloth.

(2) The phenomenon occurs only on warmer surfaces of walls which are exposed on the other side to out-of-doors or to colder rooms.

(3) The steeper the temperature gradient through the wall, the more pronounced is the phenomenon.

(4) The light streaks, the spaces comparatively free from dust, occur over laths and joists, the dark streaks over the spaces between them.

Poynting and Thomson ("Text-book of Physics: Heat," p. 152) suggest "that the phenomenon is a probable illustration of radiometer action.'" The areas of plaster backed up by wood are probably warmer than those areas not so protected. From the supposedly warmer area an approaching dust particle is repelled by a more vigorous molecular bombardment than it encounters upon approaching the supposedly colder area.

I was led to inquire whether this explanation is a complete one upon observing what appears to be a related phenomenon. In a room rather free from dust but quite damp, the areas of plaster which ordinarily would be streaked with dust were quite clean, but were much discoloured by water. This observation

raises the question as to whether condensed water vapour may not be the trap which catches the dust. I contemplate carrying out a series of experiments to answer the following questions:

(1) Under given conditions what difference of temperature exists between a plaster area backed up by lath, and an adjacent area not so protected?

(2) What part does the presence of water vapour in the air play in the phenomenon?

(3) Can a reversal" of the phenomenon be produced? THOMAS D. COPE.

University of Pennsylvania, Philadephia,
December 18, 1914.

Curious Forms of Ice.

ON December 30, 1914, when a heavy rainfall had been followed by a night frost, a layer of prismatic ice was seen immediately below the surface of the heaps of loose clay, in shallow workings in clay-withflints at the south-west end of Walton Heath, Surrey. The workings are near the crest of the North Downs, at an elevation of about 600 ft. The ice varied from

to 1 in. in thickness, and resembled the form of calcite known as "beef," but even in the most compact portions the prisms were not in close contact with one another. When observed, about midday, the ice was melting, and the sides of some of the heaps were strewn with isolated prismatic and acicular crystals of ice.

This prismatic layer of ice is similar to the ice pillars described in NATURE (vol. lxxiii., 1906, pp. 464, 485, and 534), and analogous to the masses of fibrous ice connected with lumps of chalk, recorded in NATURE (vol. lxxxviii., 1912, pp. 484 and 517).

PLAN.

On the same occasion, shallow pools of rain-water on Walton Heath and Headley Heath were seen to be covered with thin ice, which showed a series of concentric markings parallel to the margin. These markings were formed by ridges on the lower surface of the ice, presenting an abrupt face toward the margin and a gentle slope toward deep water. The ice in the ridges contained air bubbles. The ridges were about 4 in. apart, and in some places as many as seven in number. At points where the direction of a ridge changed, as at B in the figure, a tongue of ice projected downward

SECTION AT A.

SECTION AT B.

and sometimes supported horizontal rods of ice half an inch below the surface.

These projections may be analogous to the "bulb formation referred to by writers in NATURE (vol. Ixxxviii., 1912, pp. 414 and 492, and vol. lxxxix., 1912, p. 34). The ridges differ in cross section and direction from those described in NATURE (vol. xc., 1912, p. 411). The pools did not show signs of loss of water by percolation. At first sight I regarded the ridges as earlier shore lines, marking successive extensions of the pools as water flowed into them, but the parallelism and equal spacing of the ridges are perhaps against this view. They may possibly be due to ripples. G. M. DAVIES. Birkbeck College, London, January 12.

The Fireball of December 31, 1914.

I AM writing to tell you that I also observed the fine meteor described in NATURE of January 7 (p. 517) as having been seen at Bexley Heath on December 31 at about 11.15 p.m. I saw it from my window, facing the west, and I cannot better your description of it as "a fireball, much brighter than Venus.'

Its course was from north to south, rather low down, and the sky at the time was clear above, but misty below. The meteor disappeared without leaving a luminous track behind, and seemed to dip into the mist.

I did not notice what stars it passed near, as the moon was shining; possibly there were not many just then distinctly visible.

FRANCES M. HARVEY. 15 Purland Chase, Ross, Herefordshire. THE PHILADELPHIA MEETING OF THE AMERICAN ASSOCIATION.

THE sixty-sixth meeting of the American

Association for the Advancement of Science was held at Philadelphia, Pa, on December 28, 1914 January 2, or, as it is termed, during the Convocation Week, 1914-15, under the presidency of Dr. Charles W. Eliot, President Emeritus of Harvard University. The Section on Education of the A.A.A.S. is a comparatively new one, and this was the first meeting at which a member of this section has been president of the Association.

The meetings were, almost without exception, held in the commodious buildings of the University of Pennsylvania; the only exceptions being the meetings of Section E of the Geological Society of America and the Palæontological Society of America, which were held at the Academy of Natural Sciences in the central part of the city.

At the opening session, December 28, 1914, the meeting was opened by the retiring president, Prof. E. B. Wilson, of Columbia University, who introduced president-elect Eliot. Addresses of welcome were given by Dr. E. F. Smith, Provost of the University of Pennsylvania, by Dr. W. W. Keen, President of the American Philosophical Society, by Dr. S. G. Dixon, President of the Academy of Natural Sciences, and by Mr. J. M. Dodge, representing the Franklin Institute.

Dr. Eliot replied to these addresses, and the retiring president, Dr. Wilson, then delivered his address on the subject "Some Aspects of Progress in Modern Zoology," which is printed elsewhere in this issue of NATURE.

After the adjournment of the meeting, the provost of the University and Mrs. Smith received the association and its affiliated societies in the University Museum.

The meeting was a very large one, possibly the largest in the history of the association. Registration figures indicate that there must have been more than two thousand scientific men and women in attendance. The number of affiliated societies meeting at the same time and place was also unusually large. It included the following societies:

Society of American Bacteriologists, Entomological Society of America, American Association of Economic

Entomologists, Botanical Society of America, American Phytopathological Society, American Psychological Association, Society of American Zoologists, American Society of Naturalists, American Microscopical Society, American Physical Society, Geological Society of America, Palaeontological Society of America, American Folk-Lore Society, American Fern Society, Sullivant Moss Society, American NatureStudy Society, School Garden Association of America, American Alpine Club, American Anthropological Association, Southern Society for Philosophy and Psychology, Society for Horticultural Science, American Federation of Teachers of the Mathematical and the Natural Sciences, Society of Sigma Xi.

The meeting as a whole emphasised more than ever the importance of symposia for broad topics which bring together men of different sections. A number of these were held during the week, as follows:

Section B and the American Physical Society, on the subject, "On the Use of Dimensional Equations.”

Botanical Society of America and the American Phytopathological Society, on the subject, "Genetic Relationship of Organisms."

Section of Agriculture, "The Field of Rural Economics."

Section F, the American Society of Zoologists, and the American Society of Naturalists, "The Value of Zoology to Humanity."

Society of American Bacteriologists and Section K, on the subject of ventilation.

Sections C and K and the Society of American Bacteriologists, on the subject, "The Life of Lower Organisms in Relation to Man's Welfare."

There were two especially notable incidents of the meeting. The first of these was the first large meeting of the newly-established Committee of One Hundred on Scientific Research, of which Prof. E. C. Pickering, of the Harvard College Observatory, is chairman, and Prof. J. McKeen Cattell, of Columbia University, the secretary. Reports were received from a number of subcommittees, other sub-committees were established, and the work of the committee as a whole was systematised in order to cover the whole field of scientific research in America with the view of

the ultimate ascertaining of its needs. The listing and classification of research funds, the needs of research students, the co-ordination of research among educational institutions, private endowments and industrial research, and a number of other topics will be taken up by this committee.

The second notable event of the meeting was the first session of the newly-established Section of Agriculture (Section M). This opening meeting was presided over by the president of the association, Dr. Eliot. The vice-president, Dr. L. H. Bailey, formerly Director of the College of Agriculture of Cornell University, gave his address on the subject: "The Place of Research and of Publicity in in the the Forthcoming Country Life Development." The symposium which followed consisted of the following addresses: "Rural Economics from the Standpoint of the Farmer," by Hon. Carl Vrooman, Assistant Secretary of Agriculture; "Credit and Agriculture," by Prof. G. N. Lauman, of Cornell University; "Market

ing and Distribution Problems," by C. J. Brand, Chief of the Office of Markets, U.S. Department of Agriculture; and "Distinction between Efficiency in Production and Efficiency in Bargaining," by Prof. T. N. Carver, of Harvard University.

The following addresses of the presidents of sections were delivered during the week :—

(a) F. Schlesinger, "The Object of Astronomical and Mathematical Research"; (b) A. D. Cole, "Recent Evidence for the Existence of the Nucleus Atom' (c) C. S. Alsberg, "Theories of Fermentation "; (d) O. P. Hood, "Safety Engineering"; (e) J. S. Diller, The Relief of Our Pacific Coast"; (f) A. G. Mayer, "The Research Work of the Tortugas Laboratory of the Carnegie Institution at Washington"; (g) H. C. Cowles, The Economic Trend of Botany "; (h) W. B. Pillsbury, "The Function and Test of Definition and Method in Psychology"; (i) J. G. Wall, "Social and Economic Value of Technological Museums"; (k) T. Hough, "The Classification of Nervous Reactions"; (1) P. P. Claxton, "The American Rural School"; (m) L. H. Bailey, “A Place of Research and of Publicity in the Forthcoming Country Life Development."

Following the example of the British Association for the Advancement of Science, two public evening lectures complimentary to the citizens of Philadelphia and vicinity were given. Dr. D. C. Miller, of the Case School of Applied Science, lectured on Tuesday evening, December 29, on "The Science of Musical Sounds," illustrating his lecture by a large number of striking experiments. The second was given on Wednesday evening by By Dr. W. H. Nichols, of the General Chemical These lectures were rather largely attended, but Company, on "The War and Chemical Industry." the American Association has not as yet succeeded in making these lectures as important, viewed as social functions, as has the British Association.

No strikingly important matters of business were considered by the council. A few small research grants were made, and the assistance of the association was continued to the Concilium Bibliographicum Zoologicum of Zurich. It was decided to hold a summer meeting in 1915 at San the Pacific Coast Division of the American Francisco under the auspices and management of Association, the dates to be August 2 to 7. For the place of the next Convocation Week meeting (December 27, 1915, to January 1, 1916), Columbus, Ohio, was chosen. It will be remembered that the association had virtually accepted an invitation from the University and City of Toronto, Canada, for this last-named meeting, but on account of conditions arising from the war, Toronto begged to be allowed to postpone this meeting to some future and more favourable date. At the close of the meeting the following officers were elected for the coming year :

President Prof. W. W. Campbell, Lick Observatory, University of California.

Presidents of Sections: A, Mathematics and Astronomy, Prof. A. O. Leuschner, University of California; B, Physics, Prof. Frederick Slate, University of California; C, Chemistry, Prof. W. McPherson, Ohio State University; D, Engineering, Mr. Bion J. Arnold, of Chicago; E, Geology and Geography, Prof.