Prof. Magnus on the Propagation of Heat in Gases. 97 



It is known that light presents a deportment entirely similar 

 to radiant heat. If passed through a tube, it produces a far 

 greater illumination than without the use of a tube. This phe- 

 nomenon, which depends on repeated reflexion from the inner 

 side of the tube, is especially evident in the case of the so-called 

 liquid jet. Even if the tube is lined on the inside with black 

 paper, it produces, as I have found, a very surprising increase 

 in the illumination, although not so intense as the unblackened 

 tube. 



In order the better to ascertain the influence of the side of the 

 tube in the passage of heat-rays, I have investigated, in the ease 

 of each gas, the radiation, not only of the tube blackened in- 

 ternally, or rather lined with black paper, but also with the un- 

 blackened tube. i 



In the following Table the results obtained are placed opposite 

 each other for the sake of easier comparison. 



As the gas-flame could not always be obtained of exactly the 

 same intensity, the radiation of each individual gas was compared 

 with that of atmospheric air, so that both were investigated 

 directly after each other. The relation between the two is given 

 in the Table for each gas. 



In all the experiments the tube was the same, as also were the 

 glass plates by which it was closed. The determinations were 

 made in the manner described on page 88 ; the mean was taken 

 of the position of equilibrium of the needle before and after each 

 deflection, and this was subtracted from the observed deflection. 

 The mean of four such determinations for atmospheric air, and 

 of the same number for each gas, gives the relation of the radia- 

 tion between the two. 



The gases were prepared in the manner already described. 





Transmission of the Heat of a Gas-flame. 





Blackened tube. 



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 atra. pressure. 



I 



+0-5 



+07 



07 



07 



07 



-f-0-6 



07 

 07 



07 



13-2 

 13-5 

 132 

 13-5 



12-6 

 12 8 



12-5 



12-8 





+05 



+07 



07 



0-5 



06 



+06 

 07 

 07 

 07 



62-5 



630 

 627 

 630 



61 9 

 623 

 620 

 62± 







12-67 

 12-67 



Mmii 





62-15 





Corres 



ponding to ... 





Corres 



ponding to ... 



273 



Phil. Mag. S. 4. Vol. 22. No. 145. Aug. 1861. 



II 



