1872.] iSchtvendler, on Galvanotneters. 51 



3. On the lest resistance of the coils of any Differential Galvanometer. — By 

 Louis Schwendlee, Esq. 



(Abstract.) 



Mr. Schwendler gave a short outline of his investigations, stating that 

 it would be impossible for him to read the paper in full on account of its 

 intricate and purely mathematical character ; he would give, however, the 

 general results obtained and show their advantages when applied, illustrating 

 his explanations on the black board and by a Differential Galvanometer placed 

 on the table ; the paper itself would be published in Part II, of the Journal. 



In that most common form of the Differential Galvanometer, when the 

 two coils are fixed and of equal resistances and equal magnetic moments, 

 Mr. Schwendler found that the following interesting and most simple rela- 

 tion should exist between the resistance of the Galvanometer coil and the 

 resistance to be measured, in order to have the greatest possible sensibihty, 

 namely, that — 



The resistance of the Galvanometer coil should he one-third of the re- 

 sistance under measurement — supposing that the resistance of the testing 

 battery common to both the coils can be neglected against the resistance 

 to be measured. 



Mr. Schwendler remarked that the Differential Galvanometers at "present 

 employed in the Government Telegraph Department of India, have a far too 

 low resistance, and that this, to a certain extent, explained the great want of 

 sensitiveness of these instruments when used for measuring resistances higher 

 than 600 units. 



If the coils had a resistance of about 2500 units each, instead of 200 

 only, the sensitiveness of these instruments would at once be nearly trebled, 

 a fact which shows the great advantage to be derived from the apphcation 

 of Mr. Schwendler's results in the construction of Differential Galvanome- 

 ters. 



4. On the Syphon JRecorder. — By W. E. Ateton, Esq. (Abstract.) 



Mr. Ayrton said that on land telegraph lines three distinct methods are 

 employed for receiving messages. By the first the signaller sees the motion to 

 the right or left of a small magnetic needle ; by the second he hears the sound 

 of one or other of two bells of different tones, or what is virtually the same thing 

 a short or a long interval between two distinct clicks produced by a small mag- 

 netic hammer striking against a stop in its downward and upward motion ; and 

 by the third method the message is printed on a strip of paper either in ordi- 

 nary Roman letters as in the House or Hughes' instrument, or, as in the Morse 

 instrument, in a symboUcal alphabet of dots and dashes, which have to be 

 translated by the receiving signaller. 



