On some Physical Points connected with the Telephone. 281 



gradually rose in 7 hours from 12 to 26. The hydrogen-wire 

 being 2*1, and the oxygen wire 1'9 centim. below the surface, 

 at a pressure of 76 the current is 38, 



„ „ 40 „ „ 20 after 6 hours, 

 „ „ 16 „ „ 7£ after 5 hours. 



Now pressure divided by current for the last three cases 

 gives 2, 2, 2'2 respectively; or the current is directly as the 

 pressure. In the last case 7 J seems to be somewhat too low ; 

 but this may be attributed to bubbles of oxygen, which under 

 the low pressure were given off in the hydrogen tube. For 

 the first two cases, pressure divided by current gives 5'1 and 

 5*5 respectively. It is possible that at the end of the second 

 experiment the current was very slowly rising : the further the 

 wires are from the gas, the longer, of course, does it take for 

 equilibrium to be attained. 



In this experiment the gases were introduced by stopcocks 

 into the upper parts of the branches of a U-tube, the platinum 

 wires were sealed into the lower parts of those branches, and 

 the bend of the tube had a tail by which the pressure was ap- 

 plied ; so that the gases were introduced without coming into 

 contact with the wires. The same instrument, being at hand, 

 was used in § XII., where it is called a voltameter. 



If the action of the gas-couple depends entirely on solution, 

 it is natural that the current should be proportional to the so- 

 lubility of the hydrogen — that is, to the pressure. But if 

 there is really any antagonistic force kept up by hydrogen 

 attached to the positive wire, we should expect that this force 

 would not be altered by pressure, and so the whole current 

 could not be proportional to the pressure. I suppose that when, 

 by increased pressure, the electromotive force becomes equal 

 to the maximum polarization, further increase of pressure would 

 not alter the current. 



. The Physical Laboratory, 

 University College, Londo 

 December 1877. 



XL. On some Physical Points connected with the Telephone. 

 By William Henry Preece, Vice-President of the Society 

 of Telegraph Engineers, Memb. Inst. C.E., fyc* 



THE introduction of the speaking telephone, by Alexander 

 Graham Bell, has supplied physicists with an instrument 

 of research as well as with an instrument of practical utility. 

 It is an apparatus which, for the examination of certain kinds 

 of currents of electricity, is the most delicate that has yet been 

 invented. Indeed it has rendered evident the presence of cur- 

 * Communicated by the Physical Society. 



