Prof. Magnus on the Propagation of Heat in Gases. 87 



ceediDgs of the Royal Society*' that Dr. Tyndall in London 

 was engaged with an investigation on the transmission of heat 

 through gases. As Dr. Tyndall, whose research is only just 

 announced, has experimented with tubes which were closed by 

 plates of rock-salt, I considered that the following investigation 

 was independent of that of Dr. Tyndall. 



The apparatus which I used was constructed as follows. 

 Upon the plate of an air-pump T T, fig. 2. Plate I., which 

 could be placed apart from the pump on a separate foot, a 

 thermo-electric pile was firmly fixed by means of a cork ring 

 cemented on the plate. The mounting of this pile was of 

 brass, and had an internal diameter of 24 millims. and a length 

 of 118 millims. The pile itself was only 30 millims. long. It 

 contained 56 pairs of antimony and bismuth, which together 

 formed a section of 30 millims. square. The wires from this 

 pile to the galvanometer passed through the plate insulated at 

 L L. Over the pile was a glass vessel, F G,with a broad ground edge 

 air-tight upon the plate of the pump. This was 175 millims. 

 high and 100 millims. in diameter. 



At the upper part there were two apertures, q and r, to which 

 corresponded the two tubes q q x and r r x of the brass cover G G, 

 which was fastened on the top of this vessel. These tubes were 

 30 millims. in height. In the tube q q Y right over the thermo- 

 pile S, the glass vessel AB, upon which the vessel C was fused, 

 was firmly fitted by means of a cork, and made air-tight by 

 means of caoutchouc. In the tubulure D of this vessel there was 

 a cork, through which a glass tube passed, which could be closed 

 with a stopcock H. The tube rr x contained a stuffing-box, 

 through which the round brass rod a b passed. Inside the vessel 

 F Gr, this rod was provided with a horizontal arm a c, at whose 

 end c, two circular pieces of tinplate 31 millims. in diameter 

 were fitted parallel above one another at a distance of 3 millims. 

 They served as a screen, and when the thermo-pile was to be 

 exposed, could be easily moved aside. This could be effected by 

 a horizontal arm b d, fitted at b b on the brass rod a b outside 

 the vessel F G. In order to protect the pile as far as possible 

 from the influence of external sources of heat, the vessel F G 

 was surrounded by a wide glass cylinder N M, which with its 

 broad edge was pressed on the plate. The space between both 

 vessels was filled up to N M with water, which was kept at a 

 temperature of 15° C. 



The vessel C contained boiling water, which by passing steam 

 into it was kept at a temperature of 100° ; and this formed the 

 source of heat. Its action upon the thermo-pile was indicated 



* Proceedings of the Royal Society, vol. x. p. 37- Phil. Mag. vol. xix. 

 p. 60. 



