MABE ON THE ATLANTIC OCEAiN, 135 



render it impossible for a person to know when he is in it, 

 by calculation, however well ascertained may be his latitude 

 and lonsijitudo. But by tlic thermometer, if he will only be 

 at the trouble of trying the water once or twice a day, he 

 can never be mistaken in identifying this current. I have 

 been acquainted with many ship masters who were in the 

 habit of carrying this instrument to sea with them, but who 

 never attempted to ap])ly it until they deemed themselves 

 in the neighbouriiood of soundings or of the Gulf, and were 

 consequently unqualified properly to appreciate its useful- 

 ness. For unless a person will l)c at tlie pains of making 

 his thcrmomctrical observations at least once a day, it is im- 

 possible he can avail himself of its good offices. It is only 

 from the relative temperatures and changes in them that 

 he can draw his conclusions. The extremes of, heat and 

 cold, which are not the same every year, must necessarily 

 give to the water of the ocean a corresponding tempera- 

 ture ; so that (as the foregoing Tables plainly shew) in tlie 

 same season, you will find this temperature very difllerent, 

 in difterent vears. 



