Prof. Magnus on the Propagation of Heat in Gases. 93 



If the deflections obtained with atmospheric air under a pres- 

 sure of 1 atmosphere are collated, we obtain 



14°-5, 14°-4, 14°-5, 14°-5, 14°-3, 14°-5, 14°-4, 14°-4, l4°-4, 

 14-45, 14°-4, 



the mean being 14 0, 4. 



For all other gases the deflections are less. But as the deflec- 

 tions are proportional to the intensities of the current up to 

 14°-4, and as these are proportional to the increase in tempera- 

 ture of the pile, the quantities of heat which pass through differ- 

 ent gases under the same pressure are as follows : — 



Atmospheric air . . 



14-4 or 



100 



Oxygen 



14-4 „ 



100 



Hydrogen . . . . 



13-9 „ 



96-5 



Carbonic acid . . . 



13-0 „ 



90-3 



Carbonic oxide . . 



12-8 „ 



88-8 



Protoxide of nitrogen . 



12-0 „ 



83-3 



Marsh-gas .... 



11-7 „ 



81-2 



Cyanogen . . . . 



11-7 „ 



81-2 



defiant gas . . . 



75 „ 



52-1 



Ammonia . . . . 



6-3 „ 



43-7 



As oxygen gave exactly the same value as atmospheric air, it 

 was unnecessary to examine nitrogen. 



For atmospheric air the deflections were for a pressure of — 



8 millims. = 15°-8 



9 millims. = 15 *8 



This deflection is no longer proportional to the intensity of the 

 current, but corresponds to a value of 162, the value for 1° be- 

 tween 0° and 14° being placed equal to 1. If it be assumed 

 that the radiation through vacuum would produce the same de- 

 flection, the heat which passes through vacuum would be to that 

 which passes through atmospheric air under a pressure of 1 atmo- 

 sphere, as 



16-2: 14-4 = 100: 88-88. 



In order to obtain greater certainty for this proportion, I de- 

 termined the radiation through rarefied air by interposing in the 

 conduction a wire which offered considerable resistance, in order 

 that the deflections might be smaller, and proportional to the 

 intensities of the current. In the three following determinations 

 the air was under a pressure of 4 millims. Directly before and 

 after each of them the radiation through atmospheric air under 

 a pressure of one atmosphere was determined. The correspond- 

 ing determinations are indicated by the same number. 



