Intelligence and Miscellaneous Articles. 317 



Pouillet ; we have not touched it ; but we have made a tolerably nu- 

 merous series of experiments to ascertain how the nature of the sun's 

 heat varies with the time of day — that is, with the thickness of the 

 layer of atmosphere traversed, and with the quantity of water which this 

 layer contains. A. first series of experiments was made between the 

 15th of July and the 15th of September, on fine days in which from 

 7 h 30 m in the morning to midday the atmospheric conditions under- 

 went no great changes. Under these circumstances, at Paris as well 

 as Lucerne, the sun's heat always appeared more transmissible through 

 water and through alum in the morning than it was at midday. Thus, 

 at Lucerne, on Monday, September 13, at 7 h 30 ra a.m. the sun's heat 

 passed through a glass trough containing a layer of water 0*004 

 metre in thickness in the proportion of 0*755 ; at noon the transmis- 

 sion through the same trough was not more than 0*71. In August, 

 at Paris, we obtained still more striking differences. In October, on 

 the contrary, in mornings in which the temperature was near zero in 

 the early part of the day and rose much towards the middle, the 

 differences in transmissibility were no longer apparent ; and this is 

 readily intelligible — the differences between the thicknesses of air 

 traversed by the rays in the course of the experiments being less than 

 in summer, and their influence lessened by a considerable increase 

 in the quantity of aqueous vapour. 



Our spectroscopic observations have led to results which tend to 

 confirm the preceding. At Lucerne, on the 13th and 14th of Sep- 

 tember, the maximum seemed at midday a little more distant from the 

 red than in the morning, In October, on the contrary, its position 

 seemed constant, as did also the transmissibility of the rays through 

 troughs full of water. — Comptes Rendus, November 29, 1 869. 



AVOGADRO'S LAW DEDUCED FROM THE FUNDAMENTAL CONCEP- 

 TION OF THE MECHANICAL THEORY OF GASES. BY ALEX. 



NAUMANN. 



Avogadro's law, that equal volumes of different gases at the same 

 temperature and pressure contain the same number of molecules, is 

 probably regarded by the majority of scientific chemists as the most 

 certain basis for fixing molecular and atomic weights, which enable 

 chemical compositions and chemical processes to be expressed in the 

 simplest and most natural manner. Hence it may be desirable to 

 furnish a proof that the same law may be deduced as a necessary 

 consequence from a totally different basis and in a totally different 

 manner. 



In the development of the mechanical theory of gases, Avogadro's 

 law has been used * as a simple and probable assumption. But it 

 may also be deduced as a necessary consequence from the well-founded 

 assumption that the molecules of gas are very small as compared with 

 their mean distances from each other, and behave like elastic spheres, 



* Compare Clausius, Pogg. Ann. 1857, p. 367. 



