COM^ENSATtON CUKB. 19 



feveral pieces, and be fcrewed together when Ihey are wanted. 

 Such were the inftruments Mr. Erman took with him over fe- 

 veral hundred leagues; the ftick was three lines in diameter 

 at one end, and one line at the other. This philofopher does 

 not yet know what may be the influence of the difTerent thick- 

 iiefs of the condudor. One of thefe condu6lors happened to 

 be of brafs, the other of flee! ; it did not appear to him that 

 the difference of the metal occafioned any in the refults. But 

 he purpofes making new enquiries on this fubje(^. 



Mr. Erman offers his conclufions with great diffidence: he 

 does not pretend to have formed a new theory, but only to Hate 

 bis doubts on the opinion of thofe philofophers who have attri- 

 buted the phenomena hitherto obierved to a dilengaged elec- 

 tricity in the atmofphere. He notices feveral other interefting 

 experiments which he is employed in making upon fmoke, and 

 particularly on ele6lricity in a vacuum. We fliall hafteii 

 to publifli the refults of them as foon as they come to hand. 



JDefcriplion qf a Compenfation Curb, By Mr. James Scott, 



<• 



To Mr. NICHOLSON. 

 SIR, 



Inclosed I fend you a Iketch of an inftrument I havefn^fo«l"^«"y 

 conftrudled, much wanted in the profeflion of watchmaking, 

 for the purpofe of publiftiing in your Philofophical Journal, 

 which I prefume will be of much benefit to the public, and 

 at the fame time may prevent any other perfon from claiming it. 



I ftiall call it a compenfation curb. The conftru^ion of 

 this inftrument is for the purpofe of expanding and contracting 

 in the different temperatures, fo as to counteract the error 

 which the pendulum-fpring is liable to by the fmalleft variation 

 of heat or cold. 



The inventions that have hitherto been put in praftice for 

 the fame purpofe, I beg leave to make a few remarks on.— 

 The compound balance, when carefully made and adjufted, 

 is certainly a very complete counteracting expanfion, and will 

 anfwer exceedingly well on board a flilp, if there be no ma- 

 terial difference in the deniity of the airj if otherwife, the ba- 



C 2 lans;« 



letter 



