Section III., 188r). [ 111 ] ïran!<. Roy. Soc. Canada. 



IX. — I'he Longitude of the McGill College Obseroaton/. 



Bi/ Professor W. A. Eooers, Harvard College Observatory, and Professob C. H. 



McLeod, McGill College Observatory. 



(Couimuniciited by Dr .Jolmson, 'Slay 28, 1885.) 



CONTENTS. 



Part I. — By C. H. McLiîou. — Iiitroducti(jii. In.striimeiil.s at Montreal. Telegrapliic Arrangements. Plan of the 

 Work. Stars and Star Places. Personal Eciuation. Observations and Computation of Clock Errors. 



Part II. — By W. A. RouKHs. — Instruments at Cambridge. Star Places. Observations for Clock Errors. Reduc- 

 tion of Observations. Personal Eijuation. 



Part III. — By C. H. McLkod. — Clock Comparisons. Star Transits. Comljination nf results fur determination of 

 Longitude. 



PART I. 



lu March, 185*7, Lieut. Ashe, R.N., by the telegraphic tranismission of clock .signals, 

 determiued the difference of longitude between a point in Viger Ciarden, Montreal, and 

 his astronomical station at Quebec, and assigned to the former position the longitude 

 4|, 54"' 11^85 W. The pier of the transit instrument at the McGill College Observatory 

 is 5" 6 west of the station in Viger Garden, and hence the longitude of the Observatory is 

 niiide 4" 54'" 17' 45. The accepted value of the longitude of the station at Quebec rests 

 irpon a determination through the Harvard College Observatory, wherein no attempt was 

 made to eliminate the effect of the personal equation of the observers. The difference 

 between Montreal and Qiiebec was also determined without correction for personal 

 equation or interchange of observers. Owing to these circumstances some doubt has 

 always existed as to the accuracy of the result obtained by Lieut. Ashe. There is to be 

 added to the values above given, 0''.29, the reduction of the old valvie of the Cambridge 

 station to that obtained through the Atlantic cables. The corrected value of the longitude 

 of the Observatory as obtained through Qttebec is, therefore, 4'' 54'" 17'.74. 



In the summer of 1881 an unoccupied station in connection with the United States 

 Coast and Geodetic Survey was established on Mount Royal and triangulated to by the 

 late General Cutts from the stations Dannemora, in New York State, and Bellevue, in 

 Vermont. The resulting longitude of the Mount Royal station is 73' 35' 25!'20. In com- 

 municating this result Mr. Schott, assistant in charge of the Computing Division of the 

 Coast and Geodetic Survey remarks that there is no check upon it. In September, 1882, 

 the station on Mount Royal was connected with the Observatory by a trigonometrical 

 survey and a difference in longitude of 2.81 obtained. Applying this difference, we have 

 as the longitude of the Observatory from connection with the Coast and Geodetic Survey, 



