Oct. 5, 1876] 



NATURE 



5" 



every three hours, transmitting them by telegraph to the 

 station on the plain. These observations on the summit 

 and those on the plain are compared conjointly with the 

 message which arrives at midday from the Paris Observa- 

 tory. On these are based the meteorological bulletin of 

 the department. 



The station on the plain at Rabanesse is installed in a 

 house provided with a quadrangular tower of 1 5 metres 

 in height. It is provided with a large shelter for the 

 thermometers, and M. Alluard has had a fine photo- 

 graphic studio constructed, in which he intends to or- 

 ganise a regular service for photographing clouds. Other 

 ingenious and beautiful arrangements have been made 

 here, and -the entire establishment, on mountain and 

 plain, is one of the most complete in existence, and may 

 be expected to furnish much valuable meteorological 

 data. 



For the illustrations we are indebted to our French 

 contemporary, La Nature. 



ON THE APPARATUS EMPLOYED BY THE 

 LATE MR. GRAHAM, F.R.S., IN HIS 

 RESEARCHES ^ 



TV/TR. GRAHAM will probably be best remembered as a 

 •^ -*■ chemist, although the most important of his researches 

 where either purely physical, or were devoted to the elucidation 

 of questions which occupy an intermediate position between 

 physics and chemistry. It is specially interesting, therefore, to 

 observe what was the nature of the apparatus he employed in 

 obtaining results of such importance as those 

 with which his name is associated. 



From the fact that the instruments on the 

 table are those with which he arrived at all his 

 more important conclusions, it will at once be 

 evident that the appliances he used were both 

 few and simple. Before I proceed to describe 

 them, I should, as the time at my disposal is 

 veiy limited, briefly state that Graham's labours 

 were mainly devoted to ascertaining the nature 

 of molecular movement in cases in which he 

 was satisfied that no mass movement could take 

 place, and, as Dr. Angus Smith has pointed 

 out, while Dalton showed the relative weights 

 of the combining quantities, Graham showed 

 the relative magnitude of groups into which 

 they resolve themselves. It is interesting to 

 note that, as Prof. J. P. Cooke has observed, 

 while Faraday was so successfully developing 

 the principles of electrical action, Graham, 

 with equal success, was investigating the laws 

 of molecular motion. Each followed with 

 wonderful constancy, as well as skill, a single 

 line of study from first to last, and to this con- 

 centration of power their great discoveries are 

 largely due. 



The Royal Society's Catalogue of papers 

 shows that his earliest paper was on the 

 absorption of gases by liquids. It was published in 1826 

 in Thon son's "Annals of Philosophy"; in it he considers 

 that gases owe their absorption in liquids to their capa- 

 bility of being liquefied, and therefore that solutions of gases 

 in liquids are mixtiures of a more volatile with a less volatile 

 hquid. He concludes the paper by saying, that "All that is 

 insisted on in the foregoing sketch is, that when gases appear to 

 be absorbed by liquids they are simply reduced to that liquid in- 

 elastic form which otherwise, by cold or pressure, they might be 

 made to assume, and their detention in the absorbing hquid is 

 owing to that mutual affinity between liquids which is so com- 

 mon." It was a theoretical paper only, and no apparatus was 

 even described ; I have quoted it merely tsecause, in his last paper 

 in the PAil. Trans., more than thirty years afterwards, he speaks 

 of the liquefaction of gas in colloids in much the same terms. 



In 1829, the Quart^ly Journal of Science"^ contains his first 

 paper on the diffusion of gases ; he found that the Ughter a gas 



Fig. I. 



Fig. 2. 



' Lecture by W. Chandler Roberts, F.R S., Chemist of the Mint, at the 

 Loan Collection, South Kensington. 

 " Quart Journ. Sci., iL, tSag, p. 74. 



is the more quickly it diffuses away from an open cylinder. The 

 cylinders he employed were nine inches long, and 0*9 inches 

 interior diameter ; they were placed in a horizontal position, and 

 the gas under examiiution was allowed to diffuse outwards through 

 a narrow tube directed either upwards or downwards accord- 

 ing as the gas was heavier or lighter than air. It was therefore 



Fjg. 3. 



by the aid of a simple cylinder that he was led to believe, as he 

 states in this his first paper, " that the diffusiveness of gases is 

 inversely as some ftmction of their density, apparently the square 

 root of their density." He subsequently found that so great is 

 the tendency of gases to diffuse into one another, that this mix- 

 ture or inter-diffusion will take place through apertures of insen- 



FlG. 4. 



Fig. 



sible magnitude. And in his paper in 1834,1 he treats in detail 

 of diffusion through porous septa, his object being "to estab- 

 lish with numerical exactness the following law of diffusion 

 of gases : — The diffusion or spontaneous intermixture of two 

 gases in contact is effected by an interchange in position ol 

 indefinitely minute volumes of the gases, which volumes are not 



Fig. 6. 



Fig. 7. 



necessarily of equal magnitude, being, in the case of each gas, 

 inversely proportional to the square-root of the density of that 

 gas." He started from the well-known experiment of Dober- 

 einer, who found, in 1825, that hydrogen kept in. a glass 

 receiver standing over water, escaped by degrees through the 

 fissure into the stirrotmding air, the water in the receiver rising 

 ' Edin. Roy. Soc. Trans., xii., 1834, p. 323. 



