[ 293 ] 



XXXVIII. On the Polarization of Heat radiated from the Sur- 

 faces of Liquids. By Professor Magnus*. 



SINCE my communication of March 5 lastf, containing the 

 results of an investigation on the polarization of the heat 

 radiated by solid bodies when heated to 100° C, I have been 

 occupied with the examination of the heat radiated by liquids. 

 In these experiments it was impossible to employ the same form 

 of apparatus as for solids, because it was necessary for the ra- 

 diating surface to be horizontal. The whole portion of the ap- 

 paratus containing the reflecting mirror, and the box containing 

 it, was therefore placed upon a plane inclined at an angle of 35° 

 to the horizon. The radiating vessel consisted of a completely 

 closed box 12 centims. broad, 21 centims. long, and 4 centims. 

 high, which was maintained at a temperature of 100° C. by a 

 current of steam. This box w r as placed in a horizontal position ; 

 and upon it was fastened a tray of sheet iron of equal length and 

 breadth, but only 1 centim. deep. The radiating liquid was 

 placed in this tray. 



In order to test this arrangement, a plate of polished tin plate 

 was first introduced into the tray instead of the liquid. The 

 polarization of the heat radiated by this plate was found to be 

 almost exactly the same as when the former arrangement was 

 employed J, namely 25*8 and 26*0 per cent, in two experiments. 

 Also when a plate of transparent glass was placed in the tray 

 instead of a liquid, almost the same value for the polarization 

 was found as previously §, namely 11*9, 11*7, and 9'82 per cent. 

 in three experiments. Consequently this modification of the 

 apparatus gave results as trustworthy as those given by the 

 former one. Such verification of the apparatus was essential, 

 because it was not possible to give the radiant surface various 

 azimuths as with radiating solids. 



Only such liquids could be used as boil at a temperature above 

 100° C. ; and there are only a few of these which do not, at this 

 temperature, evaporate rapidly and give rise to clouds in such a 

 manner as to obstruct the radiation. Consequently the number 

 of liquids which could be employed was exceedingly small. Neither 

 amyl-alcohol, boiling at 120° C, nor aniline, boiling at 180° C, 

 could be used, on account of the formation of these clouds. The 



* Translated by Frederick Guthrie, F.R.S.E., from the Monatsbericlit 

 der koniglich preussischen Akademie der Wissenschaften zu Berlin. April 

 1868, p. 249. 



f Phil. Mag. September 1868. 



% Ibid. § Ibid. 



