34 GENEKAL VIEW AND BASIS OF SCIENTIFIC RESEARCH. 



by the largest orchestra ; and these vibrations do not 

 appear to interfere with its power of simultaneously trans- 

 mitting an almost infinite number of rays of heat, and of 

 magnetic and electric induction. In a similar manner a 

 metal wire is capable of transmitting a number of electric 

 currents at the same instant of time ; and this property is 

 being applied in electric telegraphy. 1 



The changes also produced in bodies generally by 

 alteration of pressure or temperature, even when viewed 

 by the aid of our imperfect means and extremely incom- 

 plete knowledge of its effects, are often so profound that 

 they point to the conclusion that every single substance 

 may be largely considered as a different body at every 

 different pressure or temperature; for instance, iron, 

 nickel, and manganese are magnetic at low temperatures 

 and non-magnetic at high ones ; a red acid solution of a 

 salt of cobalt changes to an intense blue colour by merely 

 warming it; hot bismuth is electro-positive to cold bis- 

 muth ; a hot solution of potash is electro-negative to the 

 same solution cold ; and it is probable that every sub- 

 stance undergoes a numerous series of molecular changes 

 when gradually altered in pressure or temperature, but we 

 have as yet detected only a few of them. 



Mineral carbonate of calcium is said to crystallise in 

 upwards of 700 different varieties of form. The self- 

 repairing power of a crystal is like that of a human being. 

 A slightly abraded crystal of alum, dipped for an instant 

 into a saturated aqueous solution of that salt, completely 

 repairs the injured parts ; and if the solution contains cer- 

 tain other salts dissolved in it, the crystal repairs itself with 

 alum only and refuses to unite with the other substances, 

 provided they do not belong to the same crystalline 



1 See Telegraphic Journal, Dec. 1875, pp. 264 and 286, 



