PROEESSOR TYNDALL’S CONTRIBUTIONS TO MOLECULAR PHYSICS. 351 
above 212° Fahr. By augmenting the resistance its heat was lowered, until it was no 
longer competent to produce the least ebullition. It was then withdrawn from the 
water, and employed as a source : the following are the results : — 
Table XXII. — Source, platinum spiral at 100° C. 
Name of vapour. Deflection. Absorption. 
O 
Bisulphide of Carbon . . 5 - 7 7'03 
Chloroform 14 - 0 16 -8 
Iodide of Methyl . . . . 15-3 18-0 
No reversal was here obtained. The temperature was then reduced so that the total 
heat fell from 81 units to 59 units ; but not even in this case (when the temperature was 
considerably below that of boiling water) could the reversal be obtained. The absorp- 
tions approach each other, but the iodide has still the advantage of the chloroform. 
Table XXIII. — Source, platinum spiral, heated under 100° C. 
Name of vapour. Deflection. Absorption. 
Bisulphide of Carbon . . . 5-2 9 -2 
Chloroform KM) 17‘3 
Iodide of Methyl .... 10-8 18-2 
It is not, therefore, temperature alone which determines the inversion : the experiments 
prove that there is a greater synchronism between the vibrating periods of chloroform 
and lampblack than between those of chloroform and platinum raised to the tempera- 
ture of the lampblack. It will be seen, however, that as the temperature of the plati- 
num falls, the opacity of the chloroform increases more quickly than that of the iodide : 
with an intensely white-hot spiral, as shown in Table XXI., the absorption of chloro- 
form is to that of the iodide as 100 : 162, while, with the spiral heated to a temperature 
of 212° Fahr., the ratio of the absorptions is as 100 : 105. 
§9. 
We have hitherto occupied ourselves with the radiation from heated solids: I will 
now pass on to the examination of the radiation from flames. The first experiments 
were made with a steady jet of gas issuing from a small circular burner, the flame being 
long and tapering. The top and bottom of the flame were excluded, and its most 
brilliant portion was chosen as the source. The following results were obtained : — 
3b 
MDCCCLXIV. 
