SCIENTIFIC AND TECHNICAL LABOURS TO 1860. 241 



vestigation and the measuring instruments underwent 



O o 



at our hands. For investigating the influence, which 

 the high pressure prevailing at great depths exerts 

 on the cable, steel tanks that could be closed were 

 constructed, and the insulation of the cables measured, 

 whilst they were subjected therein to a strong pressure. 

 The fact already observed by us during the laying of 

 the Red Sea cable was hereby confirmed, that the in- 

 sulating capacity of the gutta-percha is increased by 

 the pressure of the water, whereby the possibility was 

 established of laying submarine lines even at the 

 greatest depths. We further drew up tables for cal- 

 culating the extent of the diminution, which the insu- 

 lating capacity of gutta-percha, india-rubber and other 

 insulating materials undergoes through increasing tern- 



O O O C> 



perature, as well as for the diffusive capacity 

 specific induction - - of these insulators. Our experi- 

 ments showed that in these points india-rubber and 

 its compounds are far superior to gutta-percha, a 

 circumstance, which caused us to institute extensive 

 experiments, to obtain a good insulation of conductors 

 by coating with india-rubber, but which did not quite 

 lead to the sought-for practical results. 



A paper communicated by us in the year 1860 

 to the British Association - - entitled "Outline of the 

 principles and practice involved in dealing with the 

 electrical conditions of submarine electric telegraphs' 1 

 - summarized the main results of our inquiries, and 

 forms the foundation of the system of testing cables and 



detecting their faults which was afterwards generally 



16 



