Marine Thcrjnomeler Case. 299 



about a league. After we passed that promontory, the mercury 

 again rose to 69 fleg., at which it continued until the ship en- 

 tered the Strait of Gibraltar. In the Strait the wind was ad- 

 verse ; and, in beating through it, the mercury stood at 6S deg. 

 in the middh- of the Strait, 64 deg. on the Spanish shore, and 

 61 deg. on the African coast: this difference between the tem- 

 perature on the Spanish and African shores is apparently easily 

 accounted for, as wc stood much closer to the latter, avoiding 

 the former on account of the rocks and shoals to the westward 

 of Tariffa ; yet as we found the mercury at our anchorage in Gi- 

 braltar Bay stood at 64 deg., perhaps there really was a difference 

 of temperature in the water on the opposite shores : this was in 

 October, 1818. Major Rennell, to whom science is under so 

 many obligations, has coninmnicated to me, that Captain Beau- 

 fort, of tlie Royal Navy, found a difference of 10 deg. between 

 the wfeter in the middle of the Strait and that in Gibraltar Bay, 

 but I am not aware at what season Captain Beaufort's experi- 

 ments were made. 



Since Mr. .lamieson completed the thermometer case for me 

 I carried it down to Greenock, and exhibited it to Mr, Colin 

 Lamont, Mr. Quintin Leitch, and Mr. William Heron. Mr. 

 Leitch procured a boat, and we went off, and made a number of 

 experiments, which proved completely satisfactory. 



My opinion of Jamieson's Marine Thermometer Case is, that 

 the simplicity of its construction, and its strength, render it as 

 complete a thing as could be desired for the purpose for which 

 it is intended. I fully concur in the opinion expressed in the cer- 

 tificate by Messrs. Lamont, Leitch, and Heron ; and I am de- 

 cidedly of opinion that either to increase the size, or to add lead 

 to it to increase the weight, will never be proposed by any prac- 

 tical seaman. 



The mode in which I propose to use the apparatus is, by 

 making about 20 fathoms of strong line fast to it, — to cause the 

 olhcer of the watch to stand aft with the end of the line made 

 secure to one of the staunchions, or some other thing, lest it 

 should accidentally slip through his hands, and the whole be 

 lost : he must then cause the apparatus to be passed forward, as 

 in heaving the deep sea lead : when the vessel has much way 

 through the water, it may be passed to the bows|)rit end, and 

 dropped (not hove) from it ; but for general use the fore-chains 

 may be far enough : when all is ready, let the olhcer call out to lei 

 go, and when that is done he must immediately haul in the line, 

 and when he gets hold of the case, open it, and draw out the 

 thermometer a suflicicnt length to read off the altitude of the 

 mercury indicated by the scale, which he ought iuuncdialely to 

 1* p 2 mark 



