November 1 8, 1909] 



NA TURE 



67 



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.] 



The Temperature of the Upper Part of Clouds. 



At the recent meeting of the British Association, a report 

 of which appeared in .Nature of October 14 (p. 473), Prof. 

 A. L. Rotch gave an account of the highest balloon ascent 

 iii America. It is stated he found the remarkable result 

 lliat on at least two ascents the temperature increased 

 in a cumulus cloud in passing upwards. It is stated that 

 during the discussion ol the paper doubt was expressed as 

 10 the reality of the phenomenon. The first thing that 

 .strikes one on reading Prof. Rotch 's result is that it 

 seems rather curious that this phenomenon had not been 

 recorded in previous ascents. When one considers the con- 

 ditions, it is only what might be expected. The upper part 

 of the cloud is receiving and dealing with the whole solar 

 r.-idiation falling on its surface, as none of it passes through 

 il. .Some of this heat penetrates some distance into the 

 cloud, where it undergoes repeated reflections from the 

 cloud particles. One would thus expect that the cloud 

 particles and the saturated air would absorb some of the 

 heat and have their temperature raised, though probably 

 llie greater part of the heat is reflected into space. 



There is, however, a point to which I wish to direct 

 attention, and that is to the extreme difticulty of getting 

 anything like correct records of temperature and humidity 

 ill the conditions e.xisting at the top of cumulus clouds. 

 On one occasion, while making observations on Pilatus 

 Kulm, the top of the mountain being at the time in dense 

 cloud, but evidently near its upper limit, part of the 

 observations consisted in taking readings of wet- and dry- 

 bulb thermometers, but under the conditions it was found 

 10 be very difKcult to get trustworthy results. All sorts 

 of abnormal and contradictory readings were at first 

 obtained, even to the wet-bulb reading higher than the 

 dry. A few observations of the surroundings cleared up 

 (he difficulties. To begin with, one felt as if in an oven. 

 Radiant heat streamed in from every direction, though 

 no sun v/as visible, not even the direction of it. An 

 examination of the surfaces of surrounding objects showed 

 them to be in a very abnormal condition, though in the 

 midst of dense cloucl many of them were perfectly dry, 

 not the usual dripping condition. The heat reflected from 

 the cloud particles was absorbed by the surrounding 

 objects, and their temperature raised far above the dew 

 point. For instance, a thermometer placed on a large 

 I)iece of wood showed a temperature of 60° F., while if 

 iuing up near it only rose to 48°. 



Under the conditions the diffused radiation acted on all 

 surfaces and raised their temperature, but, of course, did 

 not raise them all to the same amount, large bodies, as 

 is well known under these conditions, being much more 

 highly heated than small ones. For instance, ordinary 

 pins driven into a wooden post for hanging the thermo- 

 meters on got wet, while the post was quite dry. All 

 olher freely exposed small objects were wet, and all large 

 ones dry. It was while the thermometers were hung on 

 the post that the wet bulb read higher than the dry, the 

 reason being that the dry was not really dry, but had a 

 film of water over it ; and it was colder than the wet 

 bulb, because it was a little smaller, and the wet had also 

 the advantage of a better heat-absorbing surface in its 

 muslin covering. The wet- and dry-bulb temperatures 

 could only be obtained after they had been properly pro- 

 tected from all radiation. In ordinary cloud observations 

 no such protection is required. 



As be.iring on the question of the heat absorbed by 

 clouds, it may be mentioned that while the observations 

 were being made on Pilatus Kulm the atmosphere was 

 in a constant state of boil, so to speak. Vertical 

 currents were constantly surging up on one side or 

 (lie other, though there was no wind. These vertical 

 currents were probably due to the disturbing effects of the 

 absorbed heat, and they seem to suggest that this heated 

 upper cart of the cloud'mav explain the formation of those 

 NO. 2090, VOL. 82] 



pillar-like clouds sometimes seen rising from sunlit 

 cumulus by the hot part breaking away from the body of 

 the cloud and rising high above it. John Aitken. 



Ardenlea, Falkirk. 



Lines of Force and Chemical Action. of Light. 



The fact that carbon dioxide is dissociated at the low 

 temperature of the surrounding medium, when green organs 

 of plants are exposed to sunlight, has been often con- 

 sidered as somewhat paradoxical. Count Rumford was the 

 first who' tried to account for it by suggesting that this 

 process takes place in spaces so small that the temperature 

 produced by the absorption of light may approach the 

 highest temperatures obtainable in our laboratories. More 

 recently I tried to adduce in support of this ingenious 

 interpretation some considerations, derived from the experi- 

 mental study of the actual conditions of this photo- 

 chemical process.' Still more wonderful is the possibility 

 of its going' on, though very slowly, in diffused sunlight. 

 But perhaps in the vifhole range of photo-chemical 

 phenomena there is no fact more wonderful than the pos- 

 sibility of obtaining photographs of the remotest star or 

 nebula. 



All these photo-chemical riddles seem to me to find their 

 full explanation in Sir Joseph Thomson's theory," so 

 eloquently expressed in his recent presidential address to the 

 British Association at Winnipeg.' 



If " a wave of light may be regarded as made of groups 

 of lines of electric force," if "in the wave front there 

 cannot be uniformity," and " it must be more analogous 

 to bright specks on a dark ground than to a uniformly 

 illuminated surface," then it becomes evident that the 

 chemical effect of light on a single molecule cannot fall off 

 in the same ratio as the dispersion of light in space. A 

 single molecule lying in the path of a line of force mav 

 be, with regard to the distant sun or star, in the same 

 condition as another molecule in the nearest proximity of 

 these centres of energy. It will be only the number of 

 molecules attacked that will be reduced WNth the increas- 

 ing divergence of the lines of force, and this result can be 

 compensated by prolonging the exposition. It seems to me 

 that Sir Joseph Thomson's theory furnishes for the first 

 time a real explanation for the fact that a ray of light is 

 not deprived of its photo-chemical efficiency, no matter how- 

 great the distance between the source of energy and the 

 molecule acted upon.* These considerations may give 

 us perhaps a deeper insight into the part played by radiant 

 energy in the chemistry of the universe than we possess 

 until now. 



A full discussion of the problem would require, of course, 

 something more than the very modest scientific equipment 

 of a botanist, and I should be very grateful if a more 

 competent reader of N.\ture would find it worth while to 

 decide the question whether the conclusions here deduced 

 are really consistent with Sir Joseph Thomson's theory. 



University, Moscow. C. Timiriazeff. 



The Position of the Radioactive Elements in the 

 Periodic Table. 



Many arrangements have been suggested, which include 

 the radio-active elements in the periodic table. So far as 

 I am aware, these have all attempted to confine each space 

 in the table to a single element. This restriction has led 

 to unlikely assumptions, on account of the large number 

 of these elements, and the limited number of spaces vacant 

 preceding uranium. 



From analogy with organic compounds it seems possible 

 that different internal structures of the atoms of the heavier 

 elements may exist, resulting in elements of the same 

 weight with perhaps very different properties. Similarly. 



' In wv Croonian lecture on " The Cosmical Function of the Green 

 Plant" (Proc. Roy. Soc, vol. Ivxii., p. 454). 



2 " Electricity and Matter." (1903.) 



•* Nature. August 26, p. 253. 



■* For instance, it seems to me that the following lines, though referring to 

 photo-electric, may he as well applied to photo-chemical phenomena : " . . . 

 thus any effect which can be produced by a unit by itself will, when the 

 source of light is removed to a greater distance, talce place, less frequently 

 it is true, but when it takes place it will be of the same character as wten 

 the intensity of light was stronger." .Sir Joseph Thomson, " On the lonisa- 

 tion of Gases by Uitra.yiolet Light, &c." (Proceedings of the Cambridge 

 Philosopliical Society, vol. xiv., part iv., p. 421). 



