232 A. Carpenter— T^e Mean Temperature of the, Src. [No. 2, 1887.] 



Record Book, it was seen that the cast was given a value of only " fair," 

 whilst a remark was made that '' the wire appeared to have lain on the 

 bottom," too light a weight having been used to shew the instant of 

 contact. The opportunity offered soon after of making another cast on 

 the same spot with an improved sounding machine, when a depth of 

 912 fathoms was obtained with a temperature differing only one degree 

 from that of the former cast. 



Whilst taking some soundings east of the Andaman Islands in 

 November last, I found that there were two abnormal temperatures, 

 one of 41°. 7 at 782 fathoms instead of 40°.5, which is the mean at that 

 depth, and one of 41°.2 at 1010 fathoms instead of 37°.7. Both of these 

 temperatures point to the water having been warmed by passage over 

 some shallower ridge of about 740 fathoms (see accompanying plate). 



If we look at a chart of the east side of the Bay of Bengal, we see 

 that there are three inlets into this partly enclosed sea. One is only 

 150 fathoms deep, viz.^ Preparis Channel ; one is not marked with any 

 depth, viz., the Ten Degree Channel ; and one has 760 fathoms marked 

 nearly on the ridge between Acheen Head and Grreat Nicobar. The 

 two high temperatures at 782 fathoms and 1010 fathoms seem to prove, 

 so far as two observations can be a proof, that no greater depth than 

 740 fathoms exists on the ridges between Acheen Head and Great 

 Nicobar and in the Ten Degree Channel. 



A glance at the curve will show that a striking change occurs at 

 150 fathoms, and that below that depth the diminution of temperature 

 is much more gradual. 



This agrees with our observations of the depth of the surface cur- 

 rents, that is to say, of the quick-moving portion of this ocean. After 

 1200 fathoms the change of temperature becomes very slow. A line 

 joining Sandoway in Arrakan with Calingapatam on the Orissa coast 

 forms the southern limit of the 1200 fathom contour of the bottom of 

 the Bay. Down to 1200 fathoms the thermometer is a check on the 

 depth obtained, but deeper than that there is too little change. 



The mean temperature of the first 150 fathoms being a moving 

 variable* may have some influence on the climatic conditions of the 

 Bay. 



A warm surface current was met with in April in Lat. 17°.34' N., 

 Long. 88° B., where the water down to 120 fathoms was all 4 to 7 de- 

 grees above the mean, the greatest difference being at 60 fathoms. It 

 was then setting to the E. N. E. 



* By * a moving variable ' I mean that that portion of the ocean which moves 

 most rapidly has also the most varying temperature. 



