496 SPECIAL METHODS OF DISCOVERY. 



of hydro-electricity, 1 and that of the retardation of electric 

 signals by static inductive action in submarine telegraph 

 cables, arose in large commercial undertakings. The 

 retardation was first observed in the working of the cable 

 between Harwich and the Hague, and the cause of it was 

 found by Faraday, who, by investigating it, discovered, 

 in the year 1853, that under some circumstances the cur- 

 rent travelled only 750 miles per second. Sir William 

 Thomson, by subsequently investigating the phenomenon, 

 discovered that, with cables of similar section, the retarda- 

 tions are proportional to the square of the lengths. 2 



Count Kumford suggested that many valuable dis- 

 coveries might often be made by means of machinery 

 employed in arts and manufactures, if persons used their 

 observing and suggesting faculties in contriving suitable 

 experiments. In illustration of this he describes his sur- 

 prise at the great amount of heat evolved in boring a 

 brass cannon at Munich, and especially that the metallic 

 chips were hotter than boiling water. It was by means 

 of further study, and various experiments in this subject, 

 that he discovered what becomes of the energy which is 

 expended in friction, and was led to the very important 

 conclusions first, that the amount of heat which may be 

 evolved by such means from a given quantity of a substance 

 by means of friction is ' inexhaustible ; ' and, second, that 

 heat ' cannot possibly be a material substance.' 



It was by examining a particular specimen of manu- 

 factured oxide of zinc which had a peculiar yellow colour 

 that Stromeyer was led to the discovery of cadmium. The 

 circumstances of the discovery are thus described by Dr. 

 Thomson : ' To Professor Stromeyer we are indebted for 

 the discovery of the new metal called cadmium ; and the 



1 See page 493. 



3 See Nature, September 7, 1876, p. 389. 





