MI.M..IK 1.] T11K 1{.U>IATH>N> 01 H.MT1-.I) 1J)|)I1-.S. 35 



, and the more refrangible unduly spread out. But 

 in the diffraction spectrum, where the colors aiv arranged 

 side by side in the order of their wave-lengths, the centre 

 vupied by the most luminous portion of the yellow, 

 and from this point the light declines away on one side 

 in the red, and on the other in the violet, the termina- 

 tions being equidistant from the centre of the yellow 

 space. 



Now if the rays coming from shining platinum were 

 passed through a piece of glass on which parallel lines 

 had been ruled with a diamond point, so as to give a 

 diffraction spectrum, even admitting the general results 

 of the foregoing experiments to be true, viz., that as the 

 temperature rises rays of a higher refrangibility are 

 emitted, it is obvious that it by DO means follows that 

 the ray first visible should be the extreme red. Our 

 power of seeing that depends on its having a certain in- 

 tensity. Even when it has assumed the utmost brillian- 

 cy which it has in a solar beam, it is barely visible. We 

 ought, therefore, to expect that rays of a higher refrangi- 

 bility should be first seen, because they act more ener- 

 getically on our organ of vision ; and as the temperature 

 rises, the spectrum should undergo a partial elongation 

 in the direction of its red extremity. 



I may here remark that the general result of these 

 experiments coincides exactly with that of M. Melloni 

 respecting heat at lower thermometric points. In his 

 second Memoir (Taylor's " Scientific Memoirs," vol. i., 

 p. 50) he shows that when rays from copper at 390 and 

 from incandescent platinum are compared by transmis- 

 sion through a rock-salt prism, as the temperature rises 

 the refrangibility of the calorific emanations correspond- 

 ingly increases. Those who regard light and heat as the 

 same agent will therefore see in this coincidence another 

 argument in favor of their opinion. 



