400 Canadian Record of Science. 
the only one peculiar to this work. There is another 
and more serious difficulty, arising from the large value of 
the longitude, If the time observations at the two stations 
are made simultaneously they must be on stars differing in 
right ascension (the s:dereal time at which the star passes 
the meridian )—in the case of Montreal and Greenwich—by 
fivehours. Now as the accuracy of the star places depends 
upon the going of the standard clock in the Observatory in 
which the positions were determined, there is a possible 
systematic error in the relative places of the two groups of 
stars which would, by just so much, affect the resulting 
longitude. Ifon the other hand, the same groups of stars be 
employed at both stations, i. e., the observations be 
made at the same time of day, there will be the possibility 
of error from change of rate of the clocks employed in the 
longitude work.so that in either case the uniformity of clock 
rate is concerned. The latter method has the advantage of 
greater convenience of working hours, and this, as it 
materially concerns the constancy of the observer’s per- 
sonal equation must have very great weight in the deci- 
sion as to the method to be adopted. 
In the Montreal-Greenwich work there were, in addition 
to the terminal stations, the two intermediate stations at 
the ends of the cable—the offices of the Commercial Cable 
Company at Hazel Hill, Nova Scotia and Waterville Ireland. 
The observers being designated by the letters A. B. C. D., 
the programme of work was as follows :—: 
Date Montreal Hazel Hill Waterville Greenwich 
April, 6 to 12 A &B observations for personal equation..C & D 
April, 19 to 30 A B C D 
May, 4 to 20 B A D C 
The observer B then went to Greenwich and observed 
with Dand C for personal equation, and afterwards the 
English observer C came to Montreal. 
Aug., 16 to 31 C A D B 
Sept., 4 to 17 A C B D 
