56 Transactions. 



the day. The rate deduced from two independent time-deter- 

 minations of the same night, when the temperature is practically 

 constant during the time of observation and the clock is in 

 circuit with the battery (one cell) only during that time, is 

 seldom, if ever, the same as that obtained from day-to-day 

 observations. 



In our programme we have two independent time-deter- 

 minations for each night. Each set of transits is reduced to 

 the epoch of the mean of the times of transit of the stars com- 

 prising that set. The rate which is applied for each transit to 

 the mean epoch, and for which some magnitude must be assumed, 

 is practically a vanishing quantity in the resulting clock-correc- 

 tion. The ideal time of exchange would be at that epoch when 

 the effect of rate is eliminated. But, for various reasons, this 

 is found to be impracticable. In the programme, then, of two 

 independent time-determinations, for obvious reasons the ex- 

 change was arranged to take place about midway between the 

 two epochs. 



An interpolation between the two epochs gives the clock- 

 correction at the instant required — that of the signals. This 

 assumes that the rate is constant during the interval and is 

 represented by a straight line. If extrapolation is necessary, 

 as sometimes occurs, the rate- value has less weight. It is highly 

 desirable that the temperature of the chronometer be kept as 

 uniform as possible, and, if necessary, special provision made 

 to attain this end. 



We are supposed now to have made a complete time-deter- 

 mination, and are ready for exchange of signals — that is, of a 

 comparison between the two clocks of the two stations. 



As some of the exchanges were over land lines, I shall ex- 

 plain this method of exchange first, taking the case of Van- 

 couver and Bamfield. Each of these stations was supplied with 

 a switchboard. The portable switchboard has been in use 

 many years and has given every satisfaction. On it are mounted 

 a talking relay, a signal relay, and a pony or clock relay ; the 

 last is never on any circuit but that of the chronometer with one 

 dry cell. Besides, there is an ordinary talking-key and a signal- 

 key, the latter breaking circuit when depressed while the ordi- 

 nary telegraph-key makes circuit. Along one edge of the board 

 there is a row of binding-posts for connecting with the clock, 

 chronograph, main line, and batteries, of which there are three 

 dry cells for the chronograph, and, as stated, one for the chrono- 

 meter. And, lastly, there is a three-point switch, by means 

 of which the main line can be thrown on or off the points of the 

 clock relay, and plugs to cut in or off any relay. While observ- 

 ing, the chronograph-circuit passes over the points of the clock 



