1.") 1 Prof. TyndalPs Contributions to Molecular Physics. 



inference, the position of water fixes that of aqueous vapour. 

 From the first seven Tables of this memoir, or from the resume 

 of results in Table VIII., it will be seen that for all thicknesses 

 water exceeds the other liquids in the energy of its absorption. 

 Hence, if no single experiment on the vapour of water existed, 

 we should be compelled to conclude, from the deportment of its 

 liquid, that, weight for weight, aqueous vapour transcends all 

 others in absorptive power. Add to this the direct and multi- 

 plied experiments by which the action of this substance on 

 radiant heat has been established, and we have before us a body 

 of evidence sufficient, I trust, to set this question for ever at rest, 

 and to induce the meteorologist to apply without misgiving the 

 radiant and absorbent property of aqueous vapour to the pheno- 

 mena of his science. 



§ V. Remarks on the chemical constitution of bodies with reference 

 to their powers of absorption. 



The order and relative powers of absorption of our vapours, 

 when equal volumes are compared, are given in Table X. : the 

 chemical formulae of the substances, and the number of atoms 

 which their molecules embrace, are as follows : — 



Formula. Number of atoms 



Bisulphide of carbon 

 Chloroform 

 Iodide of methyle 

 Iodide of ethyle . . 



Benzole 



Amylene .... 

 Alcohol .... 

 Formic ether . 

 Sulphuric ether . 

 Acetic ether . 

 Boracic ether . 



Here, for the first six vapours, the radiant and absorbent 

 powers augment with the number of atoms contained in the 

 molecules. Alcohol and amylene vapours, however, are nearly 

 alike in absorptive power, the molecule of amylene containing 15 

 atoms, while that of alcohol embraces only 9. But in alcohol 

 we have a third element introduced, which is absent in the amy- 

 lene ; the oxygen of the alcohol gives its molecule such a cha- 

 racter as enables it to transcend that of the amylene, though the 

 latter contains the greater number of atoms. Here the idea of 

 quality superadds itself to that of number. Acetic ether also 

 has a less number of atoms in its molecule than sulphuric ether ; 



ruiuiuiit, 



in molecules. 



CS 2 



3 



CHC1 3 



5 



CH 3 I 



5 



C 2 H 5 I 



8 



C 6 H 6 



12 



C 5 H 10 



15 



C 2 H 6 



9 



C 3 H 6 '0 2 



11 



C 4 H 10 O 



15 



C 4 H 8 O 2 



14 



BC 6 H io 3 



25 



