48 FKAGMENTS OF SCIENCE. 



8. Transmutation of Rays : l Calorescence. 



Eminent experimenters were long occupied in de- 

 monstrating the substantial identity of light and 

 radiant heat, and we have now the means of offering 

 a new and striking proof of this identity. A concave 

 mirror produces, beyond the object which it reflects! 

 an inverted and magnified image of the object! 

 Withdrawing, for example, our iodine solution, an in-' 

 tensely luminous inverted image of the carbon points o- 

 the electric light is formed at the focus of the rnirro 

 employed in the foregoing experiments. When ti 

 solution is interposed, and the light is cut away, what 

 becomes of this image? It disappears from sight 

 but an invisible thermograph remains, and it is onlj 

 the peculiar constitution of our eyes that disqualifk; 

 us from seeing the picture formed by the calorific ray; 

 Falling on white paper, the image chars itself out, 

 falling on black paper, two holes are pierced in i 

 corresponding to the images of the two coke points 

 but falling on a thin plate of carbon in vacuo, or upc 

 a thin sheet of platinised platinum, either in vacuo or i ! 

 air, radiant heat is converted into light, and the ima 

 stamps itself in vivid incandescence upon both the ca 

 bon and the metal. Eesults similar to those obtain* 

 with the electric light have also been obtained ^i 

 the invisible rays of the lime-light and of the sun. 



Before a Cambridge audience it is hardly necessaf 

 to refer to the excellent researches of Professor Stcb 

 at the opposite end of the spectrum. The above ] 

 suits constitute a kind of complement to his discove: i 

 Professor Stokes named the phenomena which h< 



1 I borrow this term from Professor Challis, 'Philoso 

 Magazine,' vol. xii. p. 621. 



