January 21, 19 15] 



NATURE 



563 



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 : — 



(i) Under given conditions what difference of tem- 

 perature 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 pro- 

 duced? Thomas D. Cope. 



University of Pennsylvania, Philadephia, 

 December i8, 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-with- 

 flints 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 

 2 to 1 5 in. in thickness, and resembled the form of 

 calcite known as "beef," but even in the most com- 

 pact 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 N.\ture (vol. Ixxiii., 1906, pp. 464, 

 485, and 534), and analogous to the masses of fibrous 

 ice connected with lumps of chalk, recorded in Nature 

 (vol. Ixxxviii., 1912, pg. 484 and 517). 



Qn 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, pre- 

 senting 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 se/en in num- 

 ber. At points where 

 the direction of a ridge 

 changed, as at B in the 

 figure, a tongue of ice 

 pr o j e c ted downward 

 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. Ixxxix., 

 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 ex- 

 tensions 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. 



NO. 2360, VOL. 94] 



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PLAN. 



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SEC TlOH Ar B. 



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 \Veek, 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 Palaeontological 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. ^L 

 Dodge, representing the Franklin Institute. 

 Dr. Eliot replied to these addresses, and the 



I 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. Regis- 

 tration 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 



j societies : — 



' Society of American Bacteriologists. Entomological 



/ Society of America, American Association of Economic 



