206 Prof. Powell on the alleged Polarization of Heat. 



lions, exceeded my most sanguine hopes, and lias furnished 

 me with the means, not only of analyzing the colours of na- 

 tural hodies, but of determining the causes from which these 

 colours originate. An account of these, and of other applica- 

 tions of it, will form the subject of separate communications, 

 and I shall confine myself at present to the single observation, 

 that, in applying this method of absorption to the decomposi- 

 tion of the solar rays, I have been able to insulate white light, 

 both in the orange and in the green space, and thus obtain 

 the most ample proof of the peculiar analysis of white light 

 which it has been the object of this paper to establish. 



By means of this analysis we are now able to explain the phe- 

 nomena observed by those who are insensible to particular co- 

 lours. (See this Journal, No. xix. Old Series, p. 153, and No. 

 ix. New Series, p. 88.) The eyes of such persons are blind 

 to red light ; and when we abstract all the red rays from a 

 spectrum constituted as above described, there will be left two 

 colours, blue and yellow, the only colours which are recognized 

 by those who have this defect of vision. To such eyes light 

 is always seen in the red space, but this arises from the eye 

 being sensible to the yellow and blue rays which are mixed with 

 the red light. 



Hence blue light will be seen in the place of the violet, and 

 a greemsh-yellow will appear in the orange and red spaces, or, 

 which is the same thing, the spectrum will consist only of the 

 yellow and the blue spectra shown in Fig. 2 and 3. The phy- 

 siological fact, and the optical principle, are therefore in per- 

 fect accordance ; and while the latter gives a precise explana- 

 tion of the former, the former yields to the latter a new and 

 an unexpected support. 



Art. III. — Further Remarks on the alleged Polarization of 

 Heat. By the Rev. Baden Powell, M. A. F. R. S. 

 Savilian Professor of Geometry in the University of Ox- 

 ford. In a Letter to Dr Brewster. 



Dear Sir, 



In the number of your Journal for July 1830, you did me the 

 favour to insert a communication on the alleged polarization 



