5 1.*2 Prof. TyndalPs Contributions to Molecular Physics. 



the lowest heat, the absorption of the latter exceeds that of the 

 former; for a bright red heat they are nearly equal, but the 

 formic still retains a slight predominance; at a white heat, how- 

 ever, the sulphuric slips in advance, and at the heat near fusion 

 its predominance is decided. I have tested this result in various 

 ways, and by multiplied experiments, and placed it beyond doubt. 

 We may at once infer from it that the capacity of the molecule 

 of formic ether to enter into rapid vibration is less than that of 

 sulphuric. By augmenting the temperature of the spiral we 

 produce vibrations of o^iicker periods, and the more of these that 

 are introduced, the more transparent, in comparison with sul- 

 phuric ether, does formic ether become. Thus w r hat I have called 

 its complexity tells upon the vibrating periods of the formic 

 ether ; the atom of oxygen which it possesses in excess of sul- 

 phuric ether renders it more sluggish as a vibrator. Experi- 

 ments made with a source of 212° Fahr. establish more deci- 

 dedly the preponderance of the formic ether for vibrations of slow 7 

 period. 



Table XVI. — Radiation through Vapours. Source, Leslie's 

 cube, coated with lampblack. Temperature, 212° Fahr. 

 Name of vapour. Absorption. 



Bisulphide of carbon . . . 6 § 4 

 Iodide of methyle .... 18*4 



Chloroform 19*5 



Sulphuric ether 54*8 



Formic ether 60"9 



For heat issuing from this source, the absorption by formic ether 

 is 6-1 per cent, in excess of that by sulphuric. 

 * Deeming the result worthy of rigid confirmation, I repeated 

 the experiments, and obtained the following deflections : — 



Table XVII. 

 Name of vapour. Deflections. 



o 



Bisulphide of carbon . . 9 '3 



Iodide of methyle . . . 25*0 



Chloroform 26*5 



Iodide of ethyle .... 34'0 



Benzole 35*5 



Amylene 46*8 



Sulphuric ether .... 47'3~\ 



Sulphuric ether .... 47 ''7 J 



Formic ether .... 49*7 1 



Formic ether .... 49-9J 



Acetic ether 51 -4 



