302 ACTION OF HEAT MODIFIED 



An expevlment hours, no sensible variation is perceptible. The late Mr. Af- 

 afier'vards ^^^^ ^^^° made a similar experiment at the house of the late 

 ''made by Ai> Mv. Aubert, and in the presence of several ingenious gentle- 

 men ; * and the result evinced the success with which he had 

 removed, by the same means, the errors arising from the ine- 

 qualities of the maintaining power. 

 Concluding The preceding statement is intended to afford a candid, 



remar .s. though not a minute account of the progress of chronometry to 



' the present day ; as far as the steps, by which the art has ad- 



vanced to its actual state of perfection, may be esteemed either 

 inventions entirely new, or essential improvements in the me- 

 thods known before. Those methods which do not admit of 

 philosophical or clear description, and also such as have not 

 yet been sufficiently established by experiment, are not con- 

 sidered as within the limits of this sketch ; and we must ob- 

 serve the same silence with regard to improvements in mere 

 workmanship, though in themselves of great practical value. 

 Tlie mechani- We cannot, however, avoid noticing, that the leading principles, 



ral problem of . j j j^ j^ mechanical solution of the problem of the lonei- 

 the longitude is J^ i = 



greatly inde')t- tude at sea has been effected, have derived a considerable part 



of *orkmen • "^ '•^'^"^ utility and success from the great perfection in the exe- 

 cution, which is a consequence of the flourishing state of the 

 trade of watchmaking ; and, under that point of view, we must 



who have thank the great wealth and maritime commerce of this country, 



teen supported ^^^ ^^^ extensive demand, which has not only promoted the ma- 



by our exten- i -i c 



pive commerce, nufactory of good watches, but created a new branch of trade, 



^'^- by a considerable demand for timekeepers for sea. 



IT. 



Account of a Series of Experiments, shewing the Effects of 

 Compression in modifying the Effects of Heat. By Sir 

 James Hall, Bart. F.R.S. Edinburgh, SfC. SfC. 



(Concluded from page 212.) 



General obser- VV HAT has been said of the heat conveyed by internal vol- 



* That experiment is generally known, and has been recently 

 mentioned in the Answer to Mr. Earnshaw, by Mr. Dalrymple. 

 p. 80. 



