190 ELECT1UCAL RADIATIONS. 



charcoal, of low conducting power, being placed near 

 another, such as copper, which is a good conductor, will, 

 in a very short time, produce, in like manner, an im- 

 pression of itself upon the metal plate. Thus any two 

 bodies, whose conducting or radiating powers are dissi- 

 milar, being brought near each other, will occasion a 

 molecular disturbance, or impress the one with the image 

 of the other. However small the difference may be, an 

 effect is perceived, and that of the most extraordinary 

 kind, giving rise to the production of actual images upon 

 each surface exposed. It is thus that a print on paper 

 may be copied on metal, by merely suspending it near^a 

 well-polished plate of silver or copper for a few days. 

 The white and black lines radiate very differently ; con- 

 sequently an effect is produced on the bright metal in 

 the parts corresponding to the black lines, dissimilar to 

 that which takes place opposite to the white portions 

 of the paper ; and, on the application of vapour, a 

 true image of the one is found impressed upon the 

 other.* 



Bodies which are in different electrical states act upon 

 each other in an analogous manner. Thus arsenic, which 

 is highly electro-negative, will, when placed near a piece 

 of electro-positive copper, readily impart to its surface 

 an impression of itself, and so in like manner will other 

 bodies if in unlike conditions. Every substance physi- 

 cally different (it signifies not whether as it regards 



by Robert Hunt: Reports of the Royal Cornwall Polytechnic 

 Society for 1842, and Philosophical Magazine, vol. xxi. p. 462. 

 On the Spectral Images of M. Closer, by Robert Hunt : Philoso- 

 phical Magazine, vol. xxiii. p. 415. 



'' Catalytic force, or altraction of surface concerned in the 

 diffusive power of gases : fin occult energy or power in saturated 

 saline solutions^ Prater. Mechanic's Magazine, vol. xlv. p. 100. 

 Ueber elektrische Abbildutigen; by G. Karsten. PoggendorfiTs 

 Annalen, vol. Ivii. p. 402. Melloni and firewater may he con- 

 sulted for much that is most remarkable connected with radiation 

 from coloured surfaces. 



