418 FRAGMENTS OF SCIENCE 



flame the bisulphide of carbon was most opaque, while 

 for all other parts of the flame the chloroform was most 

 opaque. For the radiation from a very small gas- flame, 

 consisting of a blue base and a small white tip, the bisul- 

 phide was also most opaque, and its opacity very decid- 

 edly exceeded that of the chloroform when the source of 

 heat was the flame of bisulphide of carbon. Comparing 

 the radiation from a Leslie's cube coated with isinglass 

 with that from a similar cube coated with lampblack, at 

 the common temperature of 100 C., it was found that, 

 out of eleven vapors, all but one absorbed the radiation 

 from the isinglass most powerfully; the single exception 

 was chloroform. 



It is worthy of remark that whenever, through a change 

 of source, the position of a vapor as an absorber of radiant 

 heat was altered, the position of the liquid from which the 

 vapor was derived underwent a similar change. 



It is still a point of difference between eminent investi- 

 gators whether radiant heat, up to a temperature of 100 

 C., is monochromatic or not. Some affirm this; some 

 deny it. A long series of experiments enables me to state 

 that probably no two substances at a temperature of 100 

 C. emit heat of the same quality. The heat emitted by 

 isinglass, for example, is different from that emitted by 

 lampblack, and the heat emitted by cloth, or paper, differs 

 from both. It is also a subject of discussion whether rock- 

 salt is equally diathermic to all kinds of calorific rays; the 

 differences affirmed to exist by some investigators being 

 ascribed by others to differences of incidence from the 

 various sources employed. MM. de la Provostaye and 

 Desains maintain the former view, Melloni and M. Knob- 

 lauch maintain the latter. I tested this point without 



