138 



NATURE 



{Dec. 17, 1874 



of November, the same species having long previously shed their 

 leaves in Germany. In a similar manner, the fig-trees in Lower 

 Ecypt (31° N. lat.) were partially clothed with foliage at the 

 begnining of December, and in Upper Egypt (27° N.) were still 

 in Ml leaf, whilst already, on the 24th of November, they were 

 quite bare in the Apuhan plain (41" N.). On the nth of 

 December, the pomegranate trees in the gardens of Siout were 

 in yellow leaf, and on New Year's Day, 1874, the apricot trees 

 at Farafreh were still in their prime of gt*en leaf. Hence, one 

 might readily imagine that on approaching nearer the equator 

 these same species would exhibit no interval between the fall and 

 the renewal of the foliage, and thus, to all intents and purposes, 

 become evergreen. But this phenomenon was only verified m 

 the case of the little cultivated peach trees of the oases, in which 

 it may not be constant. Moreover, the peach tree shows the 

 same tendency in mild seasons with us. In the oases, at the 

 beginning of March, when the trees began to blossom and make 

 new growth, the old leaves were still fresh and capable of assimi- 

 lation. All other deciduous trees and shrubs cultivated in the 

 gardens of Kasr Dghakel (25° 45' N. lat.), including the grape- 

 vine, apricot, apple, pomegranate, plum, fig, mulberry, and 

 willow {Salix safsaf), had lost their foliage on the arrival of Dr. 

 Ascherson, or became leafless before the end of January. It should 

 be mentioned that the fall of the leaf in this region does not 

 proceed with the same regularity as at home, for it is not un- 

 usual to see quite naked and fully clothed trees of the same 

 species standing side by side. Again, the presence of abundance 

 of moisture has the effect of enabling the trees to carry their old 

 foliage longer and put forth their new earlier than trees growing 

 in drier situations. And some of the willows growing by water 

 were quite evergreen ; that is, after the manner of the peach 

 trees mentioned above. But the apricot, one of the most abun- 

 dant trees, rarely retained even a few scattered old leaves on the 

 appearance of the flowers. The same was observed of the grape- 

 vine, fig, and mulberry. By Feb. 20 the apricot trees were in 

 full blossom, and by March 10 in full foliage, so th.at there was 

 only an interval of four or five weeks between the fall of the old 

 foliage and complete development of the new. The apple and 

 plum behaved in a similar manner, the pomegranate was a little 

 later, the fig next in order, and finally the mulberry ; whilst 

 these same things, in the reverse sense, lost their leaves first. 

 Frcm the preceding notes it seems that the fall and renewal of 

 the leaf is an essential constitutional peculiarity, which is modi- 

 fied by climatal conditions, but not entirely subject to them. A 

 more striking illustration of this fact may be found in exotic 

 deciduous trees planted in Egypt. Dr. Ascherson noted more 

 particularly the summer fall of the leaves ol Pobiscttia pulcluniina, 

 a South American shrub, and Albizzia kbbck, a native of the 

 East Indies. The former is in the full splendour of its inflo- 

 rescence in December, and quite leafless in April, remaining so, 

 it is said, until the autumn. The Albizzia is extensively planted 

 as an avenue tree. It sheds its foliage in April, but soon 

 renews it. Both of these plants lose th^ir leaves in their native 

 countries during the dry, and renew them with the opening of 

 the rainy season. 



SCIENTIFIC SERIALS 



Journal ilc Physique, III., No. 34, Oct. 1S74.— This number 

 commences with the first portion ol a paper by M. J. Bertrand, 

 entitled " Demonstration of Theorems relating to Electro- 

 dynamic Actions." The object of this paper is to simplify 

 Ampere's demonstrations of the theorems of electrodynamics. — 

 Arrangement for obtaining projections of the metallic rays and 

 their reversal, by M. Boudreaux. Instead of the electric light or 

 oxyhydrogen flame, the author employs a mixture of the chlorate 

 of the metal with one-sixth of its weight of powdered gum-lac. 

 The mixture is inflamed in a carbon crucible placed in a lantern 

 provided with a vertical slit. Reversals of the metallic lines are 

 effected by allowing a beam of white light (Drummond or sun- 

 light) to pass through the deflagrating mixture and analysing the 

 resulting rays by prisms. By allowing the sun-light to lall only 

 on one-half of the slit, the coincidence of bright with dark lines 

 can be shown. — M. Mascart contributes a paper describing two 

 pieces of apparatus for obtaining the phenomena of interlerence. 

 — On the magnetisation of steel, by M. E. Bouty. — This number 

 contains a translation of Lord Rayleigh's paper on the manufac- 

 ture and theory of diffraction gratings from iiie.- Philosophical 

 Magazine iox February and March. — Sensibility of silver bro- 



mide to rajs supposed to be chemically inactive, by H. Vogel, 

 from Poggendo^iff's Aniialen. — From the same journal there is a 

 paper by H. Streintz, on changes in the length and elasticity of 

 a wire under the influence of an electric current. — From the 

 Proc. Roy. Soc. there are translations of Prof. Tyndall's paper 

 on the transmission of sound, and Mr. Norman Lockyer's note 

 on a new class of absorption phenomena. 



Zeitsclirift der Oesterreichischen Gesellschaft fiir Metcorologie. 

 Nov. 15. — In this number Dr. Hann treats of some of the con- 

 sequences of the laws of change of temperature in air undergoing 

 change of volume. The following are some of the results of his 

 argument, which is full of interest. The rate of cooling of ascen- 

 ding air varies so much with the conditions of time and place 

 that it cannot be expressed by any general law. But both in 

 Germany and in the tropics the mean rate lies between o°'5 and 

 o°'6 C. for every 100 m.etres. Air warmed at the surface of the 

 earth does not continue to rise until it reaches a level where 

 the temperature corresponds with its own (reduced), but becomes 

 thoroughly mixed with other strata before reaching that height. 

 Temperature falls more rapidly with increase of height in bad 

 than in fine weather. In a descending current there can 

 be no condensation of moisture, and so in it the theoretical in- 

 crement of 1° C. does take place. We would expect this current 

 to clear the sky. But in fact we find that a descending current 

 often brings rain as well as warmer weather. Our moist west 

 winds do not bring their moisture from the tropics, but the 

 Anti-trade, becoming warmer as it descends, collects a fresh 

 quantity of vapour and precipitates it again when cooled by 

 radiation or ascent of mountain slopes. The formation of hail 

 and phenomena of hailstorms are best understood by supposing, 

 with Reye, the lower hot moist strata to rise rapidly to a great 

 height, not the upper air to descend, as it has been shown that 

 this would become much warmer in descending. A cold wind 

 blows first in the higher parts of the atmosphere, and the over- 

 heated air below rushes upward with unusual energy to a height 

 where precipitated moisture freezes as it falls. This ascen- 

 ding movement of warm air, and the further impulse given to it 

 by liberation of the latent heat of vapour, appear to play a large 

 part in the production and continuance of falls of rain. Dr. Hann 

 holds the barometric minimum in the middle of a storm area to be 

 a mechanical effect of the whirling movement of the air, and the 

 moving force in cyclones to be the latent heat of vapour. 



SOCIETIES AND ACADEMIES 



London 



Royal Society, Dec. 3. — "On the Coefficient of Expansion 

 of a Paraltine of high boiling-point," by G. F. Rodwell, 

 F.R.A.S., F.C.S., Science Master in Marlborough College. 

 Communicated by Prof. Stokes, Sec. R. S. 



The author, after giving an account of his researches, con- 

 cludes that paraffine is a body which undergoes a most unusual 

 expansion in passing from its ordinary solid condition to the 

 high boiling-point which it possesses. He does not remember 

 any other substance of a high boiling-point which occupies at 

 the boiling-point a volume which is one-half as large again as 

 the volume at the ordinary temperature. In an accompany- 

 ing table he has introduced, side by side with the paraffine 

 curve, the expansion curves of mercury, iodide of silver, and 

 terbromide of phosphorus, one of the most expansible liquids 

 known, if we except such bodies as ether, bromide of ethyl, 

 acetate of methyl, &c., the builing-point of which is below 100° 

 C, and which, therefore, could not be easily introduced into the 

 table for comparison with a body which boils at nearly 400° C. 



Dec. 10. — " On the effect of Heat on the Iodide of Silver," 

 by G. F. Rodwell, F.C.S. Communicated by Prof. F. Guthrie, 

 F.R.S. 



The author endeavours to prove the following main facts :— 



1. That the iodide of silver exists in three allotropic forms, 

 viz. (a) at temperatures between ilG^C. and its fusing-point, as 

 a plastic, tenacious, amorphous substance, possessing a reddish 

 colour, and transparent to light ; (jS) at temperatures below 

 il6°C. as a brittle, opaque, greenish-grey, crystalline mass; and 

 (7) if fused and poured into cold water, as an amorphous, very 

 brittle, yellow, opaque substance. 



2. That the iodide possesses a point of maximum density at or 

 about 116" C. at the moment before passing from the amorphous 

 into the crystalline condition. 



3. That if_we allow a mass of molten iodide to cool, the fol- 



