120 



tween the Observatory of St. John's College and the Cambridge 

 Observatory. 



The observations, especially those of eclipses and occultations, 

 which were made during many years by the late Mr. Catton at the 

 Observatory of St. John's College, and which have recently been 

 reduced under the superintendence of the Astronomer Royal, render 

 it a matter of some importance to determine the exact geographical 

 position of that Observatory. The simplest and most accurate means 

 of doing this appeared to be, to connect it trigonometrically with the 

 Cambridge Observatory. For this purpose, a base was measured 

 along the ridge of the roof of King's College Chapel, by means of two 

 deal rods terminated by brass studs, the exact lengths of which were 

 determined by comparison with a standard belonging to Professor 

 Miller. The extremities of the base were then connected by a tri- 

 angle, with a station on the roof of the Observatory at St. John's, 

 from which, as well as from the two former points, a signal post on 

 the roof of the Cambridge Observatory could be seen. The angles 

 at the extremities of the base, combined with the corresponding ones 

 at the station at St. John's, furnished two determinations of the 

 distance of the Cambridge Observatory, which served to check one 

 another. The meridian line of the transit instrument at St. John's 

 passes through King's College Chapel, so that by observing the point 

 at which it intersected the base, the azimuths of the sides of the 

 triangles could be immediately found. 



The result thus obtained is, that the transit instrument of the 

 Cambridge Observatory is 2313 feet to the north, and 4770 feet to 

 the west of that at St. John's College. Hence it follows that the 

 difference of latitude is 22"-8, and the difference of longitude 5"*10 ; 

 and the latitude of the Cambridge Observatory being 52° 12' 51"*8, 

 and its longitude 23"*54 east of Greenwich, we have finally for the 

 geographical coordinates of the Observatory of St. John's College, 



Latitude.. 52° 12' 29"-0 



Longitude 0° 0' 28"- 64 E. of Greenwich. 



These operations, of course, furnish incidentally, a very exact 

 determination of the orientation of King's College Chapel. The line 

 of the ridge of the roof points 6° 20''3 to the north of east. 



November 22, 1852. 



Professor Challis made a communication on the recent return of 

 Biela's Double Comet. 



December 6, 1852. 



Professor Stokes gave an account of M. de Senarmont's Researches 

 relating to the Doubly-refracting Properties of Isomorphous Sub- 

 stances. 



