392 Captain C. 0. Browne on the Determination of the 



in the manner proposed by Mr. Bull — an instrument being 

 lent by him at my request to take out to Alexandria, in order 

 to ensure the same conditions being observed at both ends of 

 the cable. 



Mr. Cromwell Varley, F.R.S., was consulted as to the par- 

 ticular character of signal that his experience in the Atlantic 

 exchanges led him to prefer. He recommended the use of the 

 signal made on the "break" of current, rather than that given 

 by the "make," because in the former case, the battery being 

 put out of circuit, the danger of irregularity due to unequal 

 resistances in the batteries employed at the terminal stations 

 would be avoided. He also advised that the transit of the beam 

 of light across a line about the middle of its stroke, where its 

 rate of motion was greatest, should be observed, rather than its 

 first movement. To do this, he proposed that the length of 

 travel of the beam should be first observed on a scale, and the 

 halfway line marked, the zero-point being brought to the 

 standing position of the beam a little before the time at which 

 each signal should be due; the current to be made for 50 seconds 

 and broken for 10 seconds, the direction of the current being 

 reversed for each successive signal. At the same time Mr. 

 Varley suggested an ingenious way of ascertaining the effect 

 of earth-currents on the signals. For this purpose the transits 

 of the beam of light across lines made at points at £ and f the 

 length of travel were to be observed. The interval of time 

 between these transits being a function of the time of retarda- 

 tion of current, a comparison of results obtained at each end 

 would give the relative effect of earth-currents or other re- 

 tarding influences. For this, however, it would be necessary that 

 the travel of the beam should be exactly the same in each case, 

 and that the observation made at these two points of the same 

 movement, which was a difficult matter, should be very accurate. 

 Besides this, a considerable number of signals might have to 

 be devoted to this work. Altogether, the Astronomer Royal 

 decided not to attempt such an investigation; but he directed 

 that one hour out of every four should be given to the obser- 

 vation of the start of the beam at the " make " and " break " 

 of currents sent in opposite directions successively every half 

 minute, that is to say, 15 seconds current and 15 seconds break, 

 followed by an opposite current and break of 15 seconds each. 

 This, taken with Mr. Varley' s method, might even give much 

 information as to earth-currents; moreover it offered the advan- 

 tage of providing a very large number of a class of signals 

 hitherto employed and found reliable and of a simple character. 

 Mr. Varley, however, strongly recommended the adoption of an 

 intermediate station as giving greater accuracy and security, 



