no PROCEEDINGS OF SECTION A. 



degree of astaticism. Some stress was laid on the fact that with 

 a little practice there is no difficulty in mounting fibres of an 

 almost indefinite length. Quartz has been tried but hitherto 

 without any appreciable advantage.* The sensitiveness attained 

 was of the order of 10'" amperes per five scale divisions. 



3. The Clark cell was used throughout as the standard of 

 electromotive force ; advantage was taken of a laborious investi- 

 gation by the author and Mr. Pollock (the subject of the next 

 paper) on the behaviour of Clai"k cells when made to yield small 

 currents. The reliability of the method was demonstrated by the 

 result of several hundred comparisons. In this application the 

 cells used were of three kinds, 



First. — Very large Clark cells used to give the known 

 currents when short circuited tlirough the megohm and 

 a galvanometer 

 Second. — Thirteen small cells having their positive plates 

 .composed of the same sample of mercury as was used 

 by Lord Rayleigh. 

 Third. — Forty similar cells with mercury electrodes from 

 another sample ; and giving identical results with the 

 Lord Rayleigh cells. 

 Li addition there were three hundred and sixty small storage 

 cells of the Hertz pattern. 



Some results for grass tree gum were given and those experi- 

 ments actually in progi'ess on sulphur were described. The 

 arrangement of the apparatus was illustrated by a diagi^am of a 

 somewhat complex character. 



4.— ON THE CLARK CELL AS A SOURCE OF SMALL 

 STANDARD CURRENTS, AND ON A GALVANO- 

 METER FOR THE PRINCE ALFRED HOSPITAL. 



By Richard Threlfall, M.A., Professor of Physics, University 

 of Sydney, and Arthur Pollock. 



[Abstract.^ 



In this paper it was shewn that when a large Clark cell is 

 short circuited thi'ough a sufficiently high i^esistance a fall of 

 Electromotive force takes place instantaneously, and this does not 

 change appreciably after the first minute or so. The fall is the 



*A repetition of the experiment resulted in a decided victory for the quartz thread. 



