LONGITUDE OF McGILL OBSERVATORY. 115 



J. Rayner Edmauds, assistant in charge of time iu the Harvard College Observatory, and 

 at Montreal, under the supervision of Professor Gr. H. Chandler. 



Plan of the Work. 



The scheme of work was drawn up by Professor Rogers. It provided for two series 

 of observations and clock exchanges of three nights each, with an interchange of stations 

 by the observers, and for personal equation observations on two nights at both stations. 



Weather telegrams were exchanged on each evening during the continuance of the 

 campaign. When there was suitable weather at both stations, the programme of opera- 

 tions was as follows: — (1) Examination of chronograph and chronograph circuits. (2) 

 Determination of the coUimation. (3) Adjustment of level of the axis of transit, when 

 necessary. (4) Star observations beginning at 1 ' 30 " p.m. A complete set of observa- 

 tions in reversed positions of the instrument to be made. (5) Exchange of clock signals, 

 beginning at ten o'clock Montreal time ; Montreal first sending signals for twelve 

 minutes and twenty seconds, beginning at a fiftieth second, and Cambridge receiving for 

 the first two minutes with the Cambridge clock out of the chronograph circuit and for the 

 remaining ten minutes with the clock in circuit ; the Montreal observer to note the 

 times of beginning and ending of his outgoing signals. This being completed, the Cam- 

 bridge clock signals wei'e sent to Montreal and there recorded on the chronograph in a 

 similar manner. (6) Star observations — a second series to be obtained in each of the 

 reversed positions of the instrument, as before the clock exchange. (7) Determination of 

 the collimation. 



By a complete set of star observations for time determination, in one position of the 

 instrument, is to be understood : two subpolar stars, two stars north of + 65" declina- 

 tion, six stars between + 20" and -l- 65°, two stars near the eqiiator and two stars south of 

 — 10'. A set of observations not to be considered available for lougitiide unless it contains 

 at least two polar stars, two south stars, and four other stars, all fully observed. The 

 level error to be determined at least every half hour, and more frequently when the iuter- 

 A'als between observations permit. 



Observing began at both stations, and the first clock exchange was made on June 

 2nd, 1883. Exchanges and time determinations were also made on June 4th and 5th. 

 Professor Rogers than came to Montreal and observed with me for personal equation on 

 two nights. The second series of observations and clock exchanges were successfully 

 made on June 20th, 21st and 23rd, Professor Rogers observing at Montreal while I 

 observed at Cambridge. On the night of June 23rd, after the exchange of clock signals, a 

 number of observational signals of star transits were also exchanged. Five stars were 

 observed at Cambridge and their transit recorded on both the Cambridge and Montreal 

 chronographs. Owing to some difficulty in the arrangement of the local circi^its, the 

 observations of these stars at Montreal were only received on the Montreal chronograph. 

 Later in the night, three stars were observed at Montreal and recorded on both chrono- 

 graphs. The observations for personal equation at Cambridge were made on June 28th 

 and 30th. 



It was found impossible to obtain two complete sets of observations before the time 

 fixed for the clock exchange, and after the second night of the campaign, the instrument 



