358 



CURRENTS, GULPH-STREAMS, &C. 



able, since the stream, from well known principles of hydraulics, 

 must gradually become wider as it gets to a greater distance from 

 the channel by which it issues. 



We have observed, that where there is an under current, it has 

 in many cases been found colder than the upper ; or rather that an 

 under current has often been conjectured to exist, from this cir. 

 cumstance. Thus on long. 31, in lat. 69, when the temperature of 

 the atmosphere, and of the surface of the sea, was 5pi Fahren. 

 Lord Mulgrave found that the water at the depth of 4038 feet, sunk 

 the thermometer to 32. And at the tropic, where the difference 

 of seasons never produces a difference of more than five or six de- 

 grees, the variation between the heat of the water at the surface of 

 the sea, and that at the depth of 3600 feet, has been found to 

 amount to not less than 31, the superior temperature measuring 

 84, and that below not more than 43. 



It is a curious fact, however, that in the northern seas, where we 

 should expect this difference to take place with the greatest pre. 

 cision, it exhibits the greatest uncertainty, the lower water being 

 sometimes warmer and sometimes colder. In proof of this we in- 

 sert the following result of the trials made by Charles Douglas, 

 Esq. of his Majesty's ship the Emerald, in the year 1769, off the 

 coasts of Norway and Lapland, as thrown into a tabular form by 

 Dr. Thomson. 



The experiments were made by letting down the thermometer 

 enclosed in a tin cylinder filled with water, and letting it remain at 



