296 On the Temperature of the Sea, 



First experiment of five hundred feet in the Atlantic Ocean. — 

 The 22d November, 1800, by 8"^ north latitude, in the middle of the 

 Atlantic Ocean, M. Dessuch and myself plunged the apparatus of 

 which I have spoken, to the depth of five hundred feet ; we were 

 not permitted by the Captain, to let it remain longer than five min- 

 utes. It took twelve minutes to draw it up ; the air was at the time 

 at +24°, Reaumur ; the surface of the sea at +24°. 3'. Our ther- 

 mometer, notwithstanding the short time it had remained in the water, 

 and that more than double that time was occupied in drawing it up, 

 and notwithstanding the influence of the water which had penentra- 

 ted the interior of our apparatus; marked only +20°.0'' : present- 

 ing a result of 4°. 3' less than the temperature of the surface. 



Second experiment of three hundred feet. 



The next day, by 7° north latitude, we tried a second experiment 

 of three hundred feet depth ; we were able to rest our apparatus at 

 that depth three hours, thanks to the flat calm we then had. In with- 

 drawing it, we found that the water, in spite of our precautions, had 

 penetrated into the interior of our apparatus, had flattened the cylin- 

 der of tin which protected our case of Avood, and that by the pres- 

 sure, our thermometer had been broken in the powdered charcoal 

 with which we had surrounded it. M. Dessuch and myself were la- 

 menting the misfortune, when it occurred to me, after having taken 

 away the fragments of the broken thermometer, to put in its place the 

 second thermometer which we had used to determine the tempera- 

 ture of the water at its surface. That expedient succeeded beyond 

 our hopes : we saw it descend rapidly from 24° where it stood at the 

 time to 13°, at which it stood a short time and then slowly remounted. 

 Thus our experiment was not altogether lost, and the results were the 

 more agreeable, as they agreed perfectly with the preceding in the 

 essential point, that the temperature of the water of the sea was much 

 more cold at three hundred feet deep than at the surface, which at 

 the time we speak of was in the air at +24°. 



That second experiment afforded us yet a new subject of pleas- 

 ure ; it confirmed us in the opinion we had entertained of the supe- 

 riority of my apparatus over the most perfect of those which had 

 previously been used, the double valved cylinder. Indeed, M. Des- 

 such, desirous of making some observations on the degree of saltness 

 at divers depths of the sea, had sunk with my thermometer, a me- 

 tallic cylmder of that kind made by Lenoir. We withdrew it full ol 

 water. The thermometer which we instantly plunged into it descend- 



