Prof. Magnus on the Propagation of Heat in Gases. 105 

 Table (continued). 



Unblackened tube. 



No. 



Position 

 of equi- 

 librium 

 of the 

 needle. 



Mean. 



Ob- 

 served 

 deflec- 

 tion. 



Differ- 

 ence. 



No. 



Position 

 of equi- 

 librium 

 of the 

 needle. 



Mean. 



Ob- 

 served 

 deflec- 

 tion. 



Differ- 

 ence. 



Atmospheric air under 1 atm. pressure. 



Under 6 millims. pressure. 



Ill 



00 



+0-2 

 +0-2 

 +0-0 

 +0-2 



+01 

 +0-2 

 +0-1 

 +01 



117 

 115 

 11-5 

 11-5 



11 6 

 11-3 

 11-4 

 11-4 



Ilia 



00 

 00 

 00 

 00 

 00 



00 

 0-0 

 00 

 O'O 



127 

 130 

 130 

 13-2 



12-7 

 130 

 130 

 13-2 



Mfian 11-4 







132 





Corres 



ponding 



to ... 



11-4 



Corresponding to ... 

 Ill: III a = ll-4: 13-2 = 100: 



132 

 113-2 



As in these determinations differences were obtained similar 

 to those already mentioned, in calculating the relation between 

 the radiation through vacuum and through different gases, I 

 have taken as a basis the values previously found and detailed 

 in page 103. In so doing I have assumed that, if 100 rays pass 

 through atmospheric air under 1 atm. pressure, by using the 

 blackened tube 102-5, and the unblackened tube 117'3, would 

 pass through vacuum. Hence of 100 rays from a gas-flame 

 which pass through vacuum, the following quantities pass through 

 the various gases under the pressure of one atmosphere : — 





Blackened 



Unblackened 





tube. 



tube. 



Vacuum .... 



. 100 



100 



Atmospheric air 



. 97-56 



85-25 



Oxygen .... 



. 97-56 



85-25 



Hydrogen . . . 



. 96-43 



83-77 



Carbonic acid . . 



. 91-81 



78-08 



Carbonic oxide . . 



. 91-85 



72-05 



Protoxide of nitrogen 



. 87-85 



75-50 



Marsh- gas . . . 



. 95-87 



76-61 



defiant gas . . 



f 64-10 

 L65-39 



59-96 

 6099 



Ammonia 



. 58-12 



55-00 



Influence of Aqueous Vapour on Badiation. 



Although it might with certainty be predicted that the small 

 quantity of aqueous vapour which air can take up at the ordinary 



