Polytechnic Association. 641 



November 16, 1871. 



Prof. S. D. Tillman, in the chair; Robert Weir, Esq.., Secretary. 



The Chairman gave notice that the meetings of the Polytechnic 

 Association would hereafter be held on Friday evening. 



The Chairman read the following notes of scientific progress : 



I. Indium. 

 Bunsen has found the specific heat of indium to be 0.057, Apply- 

 ing the law of Dulong and Petit to the result, the atomic weight of 

 indium is ascertained to be 56.7, which is a little more than double 

 the atomic weight heretofore assigned to that metal. 



II. New Mode of Illumination. 



Dr. Harcourt purposes to mix coal gas with a certain proportion of 

 air, and to allow the mixture to impinge upon platinum sponge. A 

 more brilliant light, it is claimed, is thus produced without increased 

 expense. 



Mr. Fisher inquired whether platinum sponge, exposed to a con- 

 tinued flame, would be durable. 



Dr. Van der "Weycle — I should be afraid the sponge platinum 

 would not last. The sulphur in common gas acts injuriously upon 

 platinum. Merely mixing air with coal gas reduces its luminosity. 

 Ten per cent only of common air will reduce the luminosity of gas to 

 one-half. But we can restore the luminosity by heating a substance 

 like platinum in the flame. 



The President — It will be remembered that some time ago I pre- 

 sented to this association a theory of luminosity. Scientific books 

 say that the carbon produces light because it is intensely heated. 

 That is no explanation. The theory I presented was this : Light is 

 produced by vibrations of the ether which fills all space. In ordinary 

 gas we have carbon and hydrogen united. In its combustion, the 

 hydrogen unites with oxygen and forms water. Hydrogen being a 

 gas, its combustion produces no light ; but carbon, when isolated, can- 

 not be brought into a gaseous or liquid state. It is always a solid. 

 Now, what will be the effect of the union of oxygen with common 

 gas? The carbon must leave the hydro-carbon, in which it is in a 

 gaseous state, before it unites with the oxygen, and in doing that it 

 passes from the gaseous to the solid state. It then unites with the 

 oxygen, and forms carbonic acid gas; and in doing that it passes back 



[Inst.] 41 



