ABSTRACTS OF SCIENTIFIC PAPERS 361 



XXIII. On the Construction and Submersion of Submarine Tele- 

 graph Cables. ' Journal of the Society of Telegraph Engineers,' 

 1872, vol. i. p. 114. 



This paper, which appears in the section of the Journal devoted 

 to ' Abstracts and Extracts,' and is marked ' Communicated by G. E. 

 Preece,' is substantially an abstract of (1) the first and second of the 

 Cantor Lectures (Art XX. above), and (2) the Royal Institution 

 Lecture (Art. XXII.)- 



XXIV. On a Method of Testing Short Lengths of Highly Insulated 

 Wire in Submarine Cables. ' Journal of the Society of Telegraph 

 Engineers,' 1873, vol. ii. p. 169. 



The paper describes an electrometer method of testing insulation, 

 introduced by Sir W. Thomson and Professor Jenkin during the 

 manufacture of the Western and Brazilian Company's cables, and 

 since then generally adopted in shore tests of submarine Cable core. 

 The method consists in putting the cable, charged to the full potential 

 of the battery, in connection with one pair of quadrants of a Thom- 

 son's electrometer, while the battery itself is applied to the other 

 pair. The loss of potential which the cable suffers by leakage is 

 then seen by the gradually increasing deflection of the electrometer 

 needle ; and when this becomes excessive the potential of the other 

 pair of quadrants is lowered, by the use of a resistance slide which 

 allows any convenient proportion of the battery potential to be 

 applied, instead of the whole potential. This brings back the needle 

 of the electrometer, and observations of the rate of leakage can then 

 be continued. The method has many advantages, in expedition, 

 accuracy, and convenience, over the direct process of testing by 

 means of a sensitive galvanometer ; and it has the further merit of 

 being equally applicable to cores or cables of all lengths. Several 

 cables can be tested at once, since it is only necessary to connect 

 each to the electrometer a few seconds before its potential is to be 

 observed, after which it can be disconnected and allowed to go on 

 losing charge while readings of other cables are being taken. The 

 formula for the reduction of the observations is given in the paper ; 

 the electrical connections are exhibited by a diagram ; and an example 

 of an actual test is quoted in full. 



