fMPROVEMENT IN TIME-PIECES. 205 



alteration has been conftantly favourable to the performance of 

 the tirae-keeper. I flioiild be happy in having a communica- 

 tion with you viva voce on this theme, &c. &c. 

 I am, &c. 



P. P. BARRAUD. 



That Mr. Barraud has not made this alteration in his chro- 

 nometers, in a hafty manner, will appear from the following 

 extrad taken from another of his letters. 



^ To Mr. WALKER. 

 DEAR SIR, London^ July \1 , 1800. 



SINCE we parted, I have found additional reafons to 

 believe that jewelled holes (where friclion is great) are in- 

 jurious. A box time-keeper which I have recently taken to Inftance of a 

 pieces, on its return from a long voyage, had the oil in the ^'Tl^'^^JP^""? •'^ 

 brafs holes in a much purer ftate than in the jewelled ones. In was much more 

 the former it ilill remained in a ftate favourable for adion, but/''^*^'^^'^ i^^ the 

 in the latter, the pivots were fo fixed by the tenacity of the the brafs holes : 

 oil, as to require force to extricate them ; the fteel was alfo 

 deeply ftained, and had parted with all its luftre, &c, &c. 

 I am, &c. 



P. P. BARRAUD. 



From thefe and many other obfervations made by Mr. Moft probably 

 Barraud upon the effeds of oil on time-keepers, it appears ^j^/a ^^^^'^^ °^ 

 that fmall particles of fteel are worn off by fridion in the 

 jewelled holes, and mixing with the oil, form a glutinous fub- 

 ftance that caufes the time-keeper to go irregularly. 



On the ASiion of Cold on Oils, 



IT is a known property of fome oils, that they freeze much Olive oil free«c» 

 fooner than water. The oil of olives freezes at 42^^ ^^ ^^ '^^i ^^^S'"^* 

 Fahrenheit's fcale, confequently the pureft oil of this kind 

 will lofe its fluidity fooner than that which contains fome 

 aqueous particles. Hence we may conclude, that watch- 

 makers ought to make choice of that oil which freezes with 

 the leaft degree of cold ; and as cold has no power to decom- 

 pofe olive oil, it need not be rejected on account of its having 

 aflUmed the concrete form. 



In 



