Prof. TyndalPs Contributions to Molecular Physics. 455 



but whereas the latter has but one atom of oxygen, the former 

 has two. Formic ether and sulphuric ether are almost identical 

 in their absorptive powers for the heat here employed ; still formic 

 ether has but 11 atoms in its molecule, while sulphuric has 15. 

 But formic ether possesses two atoms of oxygen, while sulphuric 

 possesses only one. Two things here suggest themselves as 

 influential on the absorbent and radiant power, which may be 

 expressed by the terms multitude and complexity. As a mole- 

 cule of multitude, amylene, for example, exceeds alcohol ; as a 

 molecule of complexity, alcohol exceeds amylene; and in this 

 case, as regards radiant and absorbent power, the complexity is 

 more than a match for the multitude. The same remarks may 

 be made with reference to sulphuric and formic ether : the for- 

 mer excels in multitude, the latter in complexity, the excess in 

 the one case almost exactly balancing that in the other. Adding 

 two atoms of hydrogen and one of carbon to the formic ether, 

 we obtain acetic ether, and by this addition the balance is turned ; 

 for though acetic ether falls short of sulphuric ether in multi- 

 tude, it transcends it in absorbent and radiant power. Out- 

 standing from all others, when equal volumes are compared, and 

 signalizing itself by the enormous magnitude of its absorption, 

 we have boracic ether, each molecule of which embraces no less 

 than 25 atoms. The time now at my disposal enables me to do 

 little more than glance at these singular facts ; but I must 

 direct the attention of chemists to the water molecule : its power 

 as a radiant and an absorbent is perfectly unprecedented and 

 anomalous, if the usually recognized formula be correct. 



§ VI. Transmission of radiant heat through bodies opake to light. 

 — Remarks on the physical cause of transparency and opacity. 



In Table III. a fact is revealed which is worth a little 

 further attention. The measurements there recorded show that 

 the absorption of a layer of iodide of methyle, strongly coloured 

 with iodine (which, doubtless, had been liberated by the action 

 of light), was precisely the same as that of a perfectly transpa- 

 rent layer of the liquid. The iodine, which produced so marked 

 an effect on light, did not sensibly affect the radiant heat emitted 

 by the platinum spiral. Here are the numbers: — 



Absorption. 



Iodide of methyle (transparent) 53*2 



Iodide of methyle (strongly coloured with iodine) . 53*2 



In this case, the incandescent spiral, or a flame, was visible when 

 looked at through the liquid ; I therefore intentionally deepened 

 the colour (a rich brown), by adding iodine, until the layer was 

 of sufficient opacity to cut off wholly the light of a brilliant jet 



