210 Intelligence and Miscellaneous Articles. 



are disposed symmetrically about this line as an axis. These ex- 

 periments serve to explain the singular circumstance, that when 

 complementary colours are produced by the aid of polarized light, 

 it is difficult or impossible to obtain a red which is entirely free 

 from a purplish hue, a quantity of white light being always ne- 

 cessarily mingled with the coloured light. In the case of the red, 

 orange, yellow, ultramarine, and purple disks, I succeeded in mea- 

 suring the amount of violet light which different proportions of the 

 white disk virtually added to the mixture, and found that it was not 

 directly proportional to the amount of white light added, but in- 

 creased in a slower ratio, which at present has not been accurately 

 determined. 



For the explanation of the above-mentioned phenomena, Briicke's 

 suggestion that white light contains a certain amount of unneutra- 

 lized red light is evidently inapplicable, since the effects are such 

 as would be produced by adding a quantity not of red but of violet 

 light ; and for the present I am not disposed to assume that white 

 light contains an excess of violet light. The explanation offered 

 by Aubert does not undertake to account for the changes produced 

 in colours other than ultramarine, and even in this case seems to 

 me arbitrary ; neither have I succeeded in framing any explanation 

 in accordance with the theory of Young and Helmholtz which 

 seems plausible. — Silliman's American Journal, August 1880. 



ON THE ABSORPTION OF RADIANT HEAT BY GASES AND VAPOURS. 

 BY MM. LECHER AND PERNTER. 



The authors discuss the different methods previously employed 

 in similar investigations, and in particular the arrangements em- 

 ployed by Tyndall, and the vapour-adhesion to which they are liable, 

 and show from numbers given by Tyndall himself how important a 

 source of error this may become. Tyndall's results often differ by 

 30 per cent., according as the whole or only half of the experimental 

 tube was polished. 



There is scarcely any other reason to be found for this difference 

 than vapour-adhesion. That a condensation of vapour along the 

 walls of the tube took place may be shown directly by comparing 

 Tyndall's observations in which the vapour-pressure was measured 

 directly, with those in which the experimental tube was filled with 

 vapour by being repeatedly placed in communication with a flask 

 containing the corresponding vapour in a state of saturation. We 

 can conclude from the absorption observed what the pressure must 

 be in the flask. We find thus for benzol-vapour, for example, a 

 tension of two atmospheres, which corresponds to a temperature of 

 100° C. But as the temperature in fact was 11° C, the excess of 

 vapour must have resulted from precipitated liquid on the sides of 

 the tube. 



The authors were led by these considerations, and by experience 

 obtained from numerous failures, to adopt finally an arrangement 

 in which the thermopile and source of heat were placed in the same 

 vessel. The influence of currents of air is rendered imperceptible 



