Proceedings of the British Association. 161 



account, the gridiron to the mercurial pendulum, especially if the 

 rods began as low as possible below the point of suspension, and 

 were carried on to the centre of gravity of the lens. He should 

 prefer the several rods to be of equal diameter, and to be coated 

 uniformly. Supposing the spring perfectly regulated, as well 

 with respect to heat as the arc, only one cause would interfere 

 with regular vibration-times. This was the effect of that part of 

 the elasticity of the air which depends on the variation of the 

 height of the barometer : — the other part, depending upon the 

 variations of the thermometer, is comprised in the adjustment for 

 the compensation for heat. There was a possibility of compen- 

 sating the former, by fastening a barometer tube to the pendu- 

 lum, and it would not be difficult to find the suitable diameter of 

 the tube : but this complication of the pendulum would be rather 

 inconvenient. At all events, the variations of the barometer were 

 not very great, especially if the specific gravity of the pendulum 

 be made as great as possible. 



Application of the principle of the Vernier to the subdividing of 

 Time) by Mr. F. Osier. A pendulum is to be used which should 

 make ten swings in the time that the principal pendulum makes 

 eleven, furnished with a small dial, and so placed that the coin- 

 cidences or want of coincidence could be observed. The strokes 

 of such a pendulum being counted, the time of every observed 

 stroke of it, reckoned back from its coincidence with the princi- 

 pal, or seconds pendulum, would, it is obvious, be found in tenths 

 of a second. 



Mr. Dent reported on his chronometrical experiment to deter- 

 mine the difference of meridians between Greenwich and Devon- 

 port. He also reported respecting his steel Balance Spring coat- 

 ed with pure gold by the electro-metallurgic process ; also of the 

 performance of his clock, in which the impulse is given to the 

 pendulum at or near the centre of percussion. By this contri- 

 vance he purposed to obviate the difficulty occasioned by the 

 freezing of the oil at low temperatures. The stopping of clocks 

 at very low temperatures had induced the Astronomer Royal to 

 invent a new escapement which seemed to answer all the condi- 

 tions required ; an addition of twelve pounds could be added on 

 to the weight of the clock, and yet a variation was produced in 

 the arc of vibration amounting to only five minutes, while an 

 addition of one pound to the weight of the ordinary Graham's 



Vol. xtiv. No l.—Oct.-Dec. 1642. 21 



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