Cambridge Philosophical Society, 



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 6"* 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. 



Nov. 22. — Professor Challis made a communication on the recent 

 return of Biela's Double Comet. 



Dec. 6. — Professor Stokes gave an account of M. de S^narmont's 

 Researches relating to the Doubly-refracting Properties of Isomor- 

 phous Substances. 



Feb. 7, 1853. — An addition was read to a paper by Professor 

 De Morgan on the Symbols of Logic, the Theory of Syllogism, &c. 



A paper was read by Mr. Denison on some Recent Improvements 

 in Clock Escapements. 



The object of this paper was to explain the construction of a new 

 remontoire or gravity escapement invented by the author, which has 

 now been in action for some time on the pendulum of the great 

 clock for the houses of parliament, and is in course of application to 

 others, both turret clocks and astronomical. 



But by way of introduction to this, which may be called the three- 

 legged gravity escapement (from the form of the scape- wheel), Mr. 

 Denison gave a description of another, which would similarly be 

 called the three-legged dead escapement, and had been previously in- 

 vented by him for the purpose of giving the impulse to the pendu- 

 lum with far less friction than usual. He found that it required only 

 Jth of the force which a common dead escapement had required to 

 make the pendulum swing the same arc. And therefore, as com- 

 pared with a gravity escapement in which there is no sensible fric- 

 tion on the pendulum, there must be still more than ^ths of the 

 force in a common dead escapement wasted, in first producing fric- 

 tion on the pendulum, and then overcoming it by an increased im- 

 pulse. The time of the pendulum would be much more disturbed 

 than it is by the inevitable variations of this large amount of friction, 

 as well as that of the clock train, but for a fortunate tendency of the 

 different errors, which are caused by these variations of force and 

 friction, to correct each other. 



