468 



Messrs. Carpenter, Jeffreys, and Thomson [Soy. 18, 



extension of the Gulf- stream, is a question which can only he resolved by 

 the determination of its relative amount in summer and in winter; and as 

 this solution could be very easily obtained (sets of Temperature-soundings 

 at every 10 fathoms down to 100 fathoms, taken in these opposite periods 

 of the year, being all that is requisite), it may be hoped that the cause of 

 this t; superheating" will not long remain undetermined. 



112. "With regard, secondly, to the Temperature of the 400 fathoms 

 beneath the superficial 100, which ranges between 5 1°- 1 and 46°' 7 in Lat. 

 49° 12*, between 4tiP*5 and 45=-3 in Lat. 56° 13', and between 47° 3 and 

 45"- 1 in Lat. 59 : 3.V, it may be pretty certainly affirmed that whilst it is 

 somewhat higher than the Isotherm of the Southern station, it is so con- 

 siderably above that of the Isotherms of the Northern stations, as decidedly 

 to indicate that the body of water between these depths has found its way 

 thither from a Southern source (see § 102). 



113. Proceeding, thirdly, to the still greater depths of which the Tempe- 

 ratures are recorded in Series 22 (1263 fath.), Ser. 19 (1360fath.), Ser. 20 

 (1443 fath.), Ser. 21 (1476 fath.\ and Ser. 35 (2090 fath.), all which are in 

 remarkably close accordance with each other, we meet with a decided 

 change in the rate of decrease of temperature at equal intervals of depth ; 

 for whilst the average of the whole five gives a reduction of no more than 

 l°-6 between 250 and 500 fathoms (that is, 0 3 '6 per 100 fathoms), the 

 reduction between 500 and 750 fathoms is 5"'4, or at the rate of 2 0, 1 per 

 100 fathoms; while between 750 and 1000 fathoms it amounts to 2r-\ t 

 brinsine dowu the temperature at the latter depth to an average of 33°*G. 

 Though the rate of diminution of temperature then becomes slower, there 

 is still a progressive decrease of temperature with increase of depth, the 

 total reduction between 1000 and 2090 fathoms being just 2°, so as to 

 bring down the temperature at the latter depth to 36~'3. 



114. "With these Series the numerous iforfowi-temperatures taken in the 

 First and Second Cruises, and tabulated in Table III., are for the most part 

 in remarkably close accordance. This accordance is greatest at depths be- 

 tween 1000 and 2435 fathoms : the temperature at the last-mentioned depth 

 showing no reduction* below that of the 2090 fathoms* sounding. The 

 accordance between the Serial and the Bottom-soundings is not so constant, 

 however, at smaller depths ; the temperature of the bottom being in several 

 instances from two to four degrees lower than that of the corresponding 

 stratum in the serial soundings. Thus in No. 24, at a depth of only 109 

 fathoms, the bottom-temperature was 46°'5, or 4° below the ordinary tem- 

 perature at that depth. In Xo. 26. at a depth of 345 fathoms, the bottom 

 temperature was 46- - 7; at least 2 Z below the average. In Xo. 23 b, at 

 664 fathoms, the bottom-temperature was 41 = '6, and in Xo. 12, at 670 

 fathoms, the bottom-temperafure was 42 C G, being in the one case about 

 2P and in the other about 1 £ c below what might have been expected at 

 those depths. These differences suggest the hypothesis that variations in 



* Its apparent ejects of 0 : 2 is quite within the limit of error of observation. 



