244 H. Wild on the Absorption of 



the other. By means of the thick copper frame upon which the 

 wire of the multiplier is wound, the oscillations of the magnet 

 were very quickly damped. Finally, the observations of the 

 deflections of the magnet were made either directly by means of 

 a telescope and superjacent millimetre- scale, placed at a distance 

 of 3 metres from the mirror, or by exhibiting the deflections in 

 a dark chamber objectively upon a translucent scale. This was 

 done by allowing the light from a gas-lamp, surrounded by a tin 

 cylinder in which a slit was made, to fall upon the mirror, and 

 by collecting the reflected light by means of a lens of great focal 

 distance, so as to produce an image of the slit upon the translu- 

 cent scale. The scale and slit were 2*3 metres from the magnet- 

 mirror. 



On each side of the thermopile a Leslie cube was placed at a 

 proper distance, its blackened side being turned thereto, and in 

 each cube water was kept boiling by means of a gas-lamp placed 

 underneath. The vapour generated in the two cubes was con- 

 ducted through glass and caoutchouc tubes into large vessels of 

 cold water. The direct influence of the gas-flames on the ther- 

 mopile was prevented by the interposition of a tin screen. Be- 

 tween the thermopile and the two sources of heat the tubes for 

 the reception of the absorbing gas were placed ; and these tubes, 

 except in a single instance, were quite symmetrically arranged 

 on the two sides of the thermopile; so that from them no inequa- 

 lities whatever in the action of the equally distant sources of heat 

 upon the thermopile could arise. 



First Series of Experiments. 



On each side of the thermopile was placed a brass tube, bright 

 inside and out, 60 centims. in length and 6 in width, the ends 

 of which were provided with perforated thin brass disks 12 cen- 

 tims. in diameter and placed perpendicularly to the axis. These 

 disks did not diminish the opening itself, but were merely in- 

 tended, in place of special screens, to prevent a direct radiation 

 from the cube outside the walls of the tube to the thermopile. 

 The ends of the two tubes were 10 centims. distant from the 

 Leslie cubes, as well as from the funnel-shaped openings of the 

 thermopile. Each of the tubes likewise possessed two lateral 

 apertures, 15 centims. from the ends, both of which were pro- 

 vided with side tubes in order to introduce and carry away the 

 gases. 



To this end, each of the lateral apertures nearest to the ther- 

 mopile were connected, by means of caoutchouc tubing, with a 

 Wohler's drying-tube ; one of the latter was filled with pumice- 

 stone moistened with concentrated sulphuric acid, whilst the pu- 

 micestone in the other w T as moistened with distilled water. These 

 two Wohler tubes were also connected by means of a fork-shaped 



