296 Description of the 



44, Adelphi-street, Hutcheson Town, Glasgow, Feb. 25, 1820, 



Dear Sir, — As I understand you have advised Mr, Jamieson, 

 mathematical instrument maker of this city, to submit the model 

 of the Marine Thennomeler Case constructed by him, for my use, 

 to the notice of the Society for the Encouragement of Arts, &c., 

 and that you have expressed a wish to have a written state- 

 ment of the causes which led to niv application co Mr. Jamieson, 

 in consetiuence of which he was led to undertake the construc- 

 tion of that instrument, and also of my opinion of its utility for 

 nautical purposes, 1 shall endeavour to comply with your wishes 

 as concisely as in my power ; though ! am much afraid the de- 

 tail into which I must necessarily enter will not admit of all the 

 brevity which might be desirable. 



My attention was first directed to the thermometer, as a va- 

 luable nautical instrument, by the excellent memoir compiled by 

 Mr. .John Purdy, hydrographer, London, to accompany the ad- 

 mirable Chart of the North Atlantic Ocean, constructed by him, 

 and published by Messrs. Whittle and Laurie, of 53, Fleet-street, 

 in the year 1812. 



The late celebrated Dr. Benjamin Franklin was, I believe, 

 the first person who suggested t!ie utility of the thermometer as 

 an indicator of the proxlmily o/j or ;ur approach to, the Ameri- 

 can coast, having remarked the great difference of temperature 

 between the water of the Gulf stream as it sweeps along the 

 coasts of the United States, and the water upon the soundings 

 between the inner edge of the stream and the shore. 



This interesting subject was afterwards taken up by Colonel 

 Jonathan Williams, who endeavoured, wit!) some success, to at- 

 tract the attention of nautical men to the vast importance of the 

 thermometer, in an ingenious work intituled " Thermometrical 

 Navigation," published at Philadelphia in 1799. 



To avoid unnecessarily extending the length of this letter, by 

 quoting evidence already before the public, 1 beg to refer to the 

 third edition of the Memoir by Mr. Purdy, already mentioned, 

 the perusal of which must satisfy the most sceptical, that the 

 thermometer is not only a certain indicator of the proximity of 

 the American coast, hut also an infallible monitor of an approach 

 to islands of ice, so perilous to navigators, and the dangers of 

 which are tenfold increased by the circumstance of their being 

 generally surrounded by dense fogs. Mr. P.'s Memoir, from the 

 Jord to the 7Sth page, is occupied with these important subjects. 



Colonel Williams recommends that the thermometer should bfe 

 slung, " so as to tow in the dead water of the ship's wake." I 

 tried this mode, and had three of my thermometers broken in 

 consequence : this led me first to think of having a case to pre- 

 vent my instruments from being fractured by any accidental con- 

 tact 



