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LXXr. A Description of a new Instrumevt for fucUitating 

 the Navigation of Ships at Sea, called " The Marine 

 Transit/' By VV. Chavasse, Lieutenant in the 6th 

 Regiment of the Madras Native Infantry. 



To Mr. Tilloch. 



Dear Sir, jLp you deem the following Descripfion of 

 the Marine Transit worthy of insertion in The Philosophical 

 Magazine, it is much at your service. 

 I ren)ain, dear sir, 



Yours very truly, 



12, Great Ciistle Streer, Cavendish Square, Wm . ChaVASSE. 



Dec. 10, 1812, 



The Marine Transit. 



The Marine Transit is intended for the same purposes 

 at sea, as the Transit Telescope on land, to afford the means 

 of ubtainina; a daily correction or adjustment of our time- 

 keepers, whereby the longitude, or a ship's position, with 

 respect to a particular meridian, may be ascertained, and 

 many useful problems relating to astronomy satisfactorily 

 solved. Should this instrument answer the end proposed, 

 the public will be indebted to the Right Honourable the 

 Lords Commissioners of the Admiralty, and the Honour- 

 able the Court of Directors of the East India Company, for 

 their fostering care in extending to me the means and pa- 

 tronage necessary to insure the trial of it under the most 

 lavouralile circumstances. 



At the beginning (jf the present year, an outline of the 

 plan was submitted to the Hicht Honourable the Lords of 

 the Admiralty, when they were pleased to order that two 

 iiistrumenls should be made under my superintentlence. 

 I have now the pleasure to announce that the same have 

 been completed by that most competent workman, Mr. 

 Thomas Jones, of Oxcndon-street, London ; and that we 

 arc emploved adjusting their rales of gointi, previous to 

 such a course of experiments on shore, as will determine 

 the propriety of taking them to sea. 



The priiiiiplt on which the instrument is constructed is 

 siir.ple, and iJiomtses, if there be no impro[)er assumption 

 in the preimses, or mistake in the reasoning, to be effica- 

 cious. 'I'hc principle in few words is this ; that equal 

 c|uaiiiities of mercury will pass through a given aperture 

 in ecpial times, if the same height of column, reckoned 



Vol. 40. No. 176. Dec. 1812. Cc fioiw 



