104; Prof. Tyndall on the Absorption and Radiation 



The extraordinary energy of boracic ether as a radiant may 

 be inferred from the last experiment. Although attenuated 

 to w^ n th of an atmosphere, its thinly scattered molecules are able 

 to urge the needle through an arc of 61 degrees, and this merely 

 by the warmth generated on the entrance of dry air into a 

 vacuum. 



Arranging the gases in the same manner, we have the follow- 

 ing results : — 



Table XLIX. 



Dynamic radiation of gases 

 at 1 atm. pressure aod a 

 common thickness of 



' ; > 



34 inches. 13' 1 inches. 



o o 



Carbonic oxide 24*4 16*6 



Carbonic acid 23*3 17'5 



Nitrous oxide 31*7 22'0 



Olefiant gas 68*0 65'0 



The influence of tenuity which renders the vapour at 0*5 of 

 an inch a more open screen than the gas at 30 inches is here 

 exhibited. In the case of the vapour, a greater length is avail- 

 able for radiation than in the case of the gas, because the radia- 

 tion from the hinder portion of the column of vapour is less 

 interfered with by the molecules in front of it than is the case 

 with the gas. By shortening the column we therefore do more 

 injury to the vapour than to the gas ; by lengthening it we pro- 

 mote the radiation from the vapour more than that from the gas. 

 Thus while a shortening of the gaseous column from 34 inches 

 to 13*1 causes a fall in the case of carbonic oxide only from 23 0, 3 

 to 17°*5, the same amount of shortening causes benzole vapour 

 to fall from 34° to 15°*1, — a much greater diminution. So also 

 as regards olefiant gas, a shortening of the radiating column 

 from 34 inches to 13*1 inches causes a fall in the deflection only 

 from 68° to 65° ; the same diminution produces with sulphuric 

 ether a fall from 68° to 36°'5 ; and with acetic ether from 73°*9 

 to 41°. In the long column acetic ether vapour beats olefiant gas, 

 but in the short column the gas beats the vapour. 



One of the earliest series of experiments of this nature which 

 were executed last autumn, though not free from irregularities, 

 is nevertheless worth recording. The experiments were made 

 with a brass tube, slightly tarnished within, the tube being 49*4 

 inches long, and divided into two equal compartments, each 247 

 inches in length, by a partition of rock-salt placed at the centre 

 of the tube. 



