PENDULUM OF COMPENSATION". O J 'Y 



N. N. &c. would be much less manageable. Not being my- 

 self a performer on any keyed instrument, I can only express 

 my approbation in general terms. Letters patent have been 

 granted for the invention. 



XI. 



A new Compensation Pendulum, without Joints or Surfaces 

 bearing against, or moving upon each other. In a Letter from 

 a Correspondent. (R. B.) 



To Mr. Nicholson. 

 SIR, 



SINCE the invention of pendulums of compensation for Pendulums of 

 changes of temperature, there nave been a number of compensation, 

 excellent contrivances, by means of the contrary expansions of 

 metallic bodies, for keeping the centres of oscillaiion and 

 suspension at an invariable distance from each other. In the Mercurial, 

 quicksilver pendulums, or any of the contrivances which re- 

 quire the use of a fluid, it may reasonably be supposed, that 

 the changes, which are to compensate each oiher, do take 

 place at the same time as the temperature beomes altered ; and 

 that the quantity and effect of the compensation continue the 

 same for any length of time, during the existence of the 

 machinery. But in pendulums composed altogether of solid 

 materials, both these results have been called in question. In GruHron pen- 

 the gridiron pendulum, it has been insisted, that the adjustment ^^''J^ object- 

 of the expansions is by the construction of holes and pins, not 

 capable of extreme exactness ; and that the variation, to which 

 the pressure of contact may be liable, and the stickage of the 

 bars, (which rub against the frame) may be more than sufficient 

 to counteract and give uncertainty to all small variations, 



required to be compensaled. And in all constructions of bars Expansion 



' ' . !>ars supposed 



of steel and brass, soldered o»- connected lengthwise, it has ^o alter by the 



been doubted—not only whether the wire-drawing and upsert- forcible action 

 •^ .• , of their parts, 



ing ot the elastic metalsthemselves, under a state otsuch severe 



force, may not allow for all small changes, without perceptible 



flexure,— but likewise whether the flexure, which in larger 



changes is perceived, may not become altered, after a course of 



time, and long exposure to the effects of heat and cold. 



Perhaps, Mr. Nicholson, you, or your readers, may be inclined 



to 



