114 ROGERS AND McLEOD ON THE 



miued immediately after leaving the hands of the maker in April, 1883, was 0M46. In 

 May, 1884, a redetermination gave a A^alue 0\160, showing a change in the form of the 

 glass. As the value of the scale still remained constant at all points, the accuracy of the 

 instrument does not seem to have been impaired. The original scale value was used in 

 the reduction of these observations. 



The Time-piece was the Blaekmau mean-time clock, by Howard. It was provided 

 with a seconds break-circuit wheel and a mintite contact maker, by means of which the 

 60th second was omitted. 



Tlie Chronograph used in the first half of the work was one of the tape form, by Messrs. 

 Cooke & Sons, York, England, but owing to the very great inconvenience experienced in 

 its use, a cylinder chronograph which, through the courtesy of Admiral Shufeldt, we were 

 fortunately enabled to obtain on loan from the United States Naval Observatory, was 

 substituted for it in the latter half of the work. The tape chronograph had a clock 

 pen and an observing pen ; the latter was also used to record the Cambridge clock 

 signals. In the cylinder instrument there was but one pen. The observing key which I 

 vised in the time observations at Montreal was arranged to make circuit. Professor 

 Rogers afterwards used the same key converted to break circuit. In order to determine 

 how the use of a make-circuit would affect my personal equation, I placed this key, 

 arranged both to make and break, in the circuit of the chronograph, which ran at about 

 one inch per second, and by mechanically adding a large number of the small intervals 

 between the make and the break, obtained an average value somewhat less than O'.Ol 

 In exchanging clock signals, the Montreal clock beats were, for the first part of the work, 

 sent out directly by the break-circuit apparatus in the clock. In the latter part of the 

 work, i.e., on the nights on which Professor Rogers observed at Montreal, the clock 

 signals were sent out through the chronograph, the end of the armature arm opposite to 

 the pen having been arranged to repeat the clock breaks. The difterence between the 

 means of the transmission times on the first three nights, and on the last three nights, is 

 probably due to the change of chronographs at Montreal. The Cambridge clock signals 

 were, in all cases, received through a relay in the main telegraph line. 



For a description of the instruments used at the Harvard College Observatory refer- 

 ence is made to Professor Rogers' report. The Cambridge time signals were transmitted 

 directly to Montreal by the clock Frodsham 1.32'7, and the Montreal signals were received 

 through a relay in the main telegraph line. 



Telegraphic Arrangement!^. 



At Montreal, the main line was brought as a loop through the Observatory and 

 grounded at the Great North Western Telegraph office. At Boston, the main line from 

 Montreal was connected, without a repeater, with the Cambridge line. The connection 

 between the two stations was therefore direct. Our very best thanks are due to Mr. Angus 

 Grant, Superintendent of the Montreal Division of the Great North Western Telegraph 

 Company, who personally performed the duties of telegraph operator at the Montreal 

 station and also provided for the free use of the lines under his control. Our thanks are 

 also due to the ofiicials of the Western Union Telegraph Company, at Boston, for the free 

 use of their lines. The telegraphic arrangements at Cambridge were -under the care of Mr. 



