280 report— 1879. 



present instrument magnifying glasses in front of the columns of ether, carrying 

 a line to guide the eye while the vernier scales and the horizontal lines which are 

 to he adjusted to the ether surfaces are drawn on glass, so as to admit of b>ht 

 shining through. This arrangement affords, therefore, a means of magnifying 

 optically the small motions of the ether, instead of doing the same hy mechanical 

 means, as has heen attempted hy some. 



11. On an improved, Bain Gauge. By N. Lowenthal Lonsdale. 



This gauge records the exact quantity of rain and snow on paper as well as on 

 a tell-tale dial. The funnel is suspended on an enclosure with a sloping roof and 

 two air pipes, within which enclosure, in winter, a small flame is kept burning to 

 melt the snow in the funnel. From the funnel the water runs into an intermediate 

 receiver, which can be closed by a valve. When open, the water rims on into 

 a larger receiver, where a float with a tube in the centre rises and falls. This 

 tube is closed at the top, aud embraces a long open tube fixed in the centre of the 

 large receiver, the two together thus forming an intermittent siphon, the diameters 

 of the inner and outer tubes of which must be, at least, as 2 to 3. To the top of 

 the float is fixed a rod with a pencil, for marking a sheet as usual. The rod also 

 moves an index which marks whole inches, and another for fractions. 



12. On a Galvanometer for demonstrating the Internal Current transmitted 

 through the Liquid within a Voltaic Cell. By Conrad W. Cooke, C.E., 

 M.S., T.E. 1 



It is of course well known that when the external circuit of a voltaic cell is closed 

 a current of electricity is transmitted through that circuit, and at the same time a 

 current of equal strength is transmitted through the liquid within the cell from one 

 plate to the other. The former of these is detected by its electro-magnetic and 

 electro-chemical effects, producing deflections in galvanometers and electroscopes 

 and sounds in telephonic instruments, and is utilised in all the applications of 

 voltaic electricity. 



As far as the author has been able to find out, there has not hitherto been any 

 satisfactory means in the hands of the demonstrator of physics by which the 

 existence of the internal cm-rent within a single cell can be made apparent. 

 Faraday, in the course of his early researches, made the following experiment : he 

 suspended a magnetic needle by a silk thread, aud lowered it into the liquid between 

 the plates of one cell of a voltaic battery, so that its length should lie in a plane 

 perpendicular to those of the plates ; and he observed that when the needle was 

 just below the surface of the liquid it was deflected the moment that the external 

 current was closed. On lowering it still deeper (the current being maintained 

 complete) its deflection gradually diminished as the depth of immersion was in- 

 creased, until it reached a position about half the depth of the liquid, when it 

 returned to zero ; and after passing this depth it was again deflected, but this time 

 in the opposite direction, its amount of deflection in either case increasing as its 

 distance from the neutral or central point was increased. The cause of this phe- 

 nomenon is obvious from the following considerations : — If a wire conveying an 

 electric current be held above and parallel to a magnetic needle, the latter, obeying 

 Ampere's law, will be deflected with an angular displacement dependent upou the 

 strength of the current and its distance from the needle ; and if the same wire be 

 held below the needle, the latter will be similarly deflected, but in the opposite 

 direction. Now the flow of electricity through the liquid in a voltaic cell may 

 (for the purpose of this explanation) be looked upon as made up of an infinite 

 number of currents transmitted in a horizontal direction from one plate to the 

 other ; and when a magnetic needle is immersed j ust below the surface of the 



1 This Paper was printed in ewtenso in Engineering, August 29, 1879, 



