CHAP. III. ] TENERIFFE TO SOMBRERO. 229 
ing-down.” Curve C is reduced from the serial sounding at 
Station I. (Plate IV.), 70 miles from Santa Cruz. The “hump” 
has now disappeared as such, but it is still represented by the 
space between C and D raising the portion of the curve corre- 
sponding with the “hump,” and representing the course of the 
southern branch of the Gulf-stream moving southward, now 
without a special impediment. Curve D represents the middle 
station of the section in the course of the trade-wind drift where 
the distribution of temperature is very regular, the isotherms 
being closely pressed together and the heated water confined to 
a thin surface layer; and the diagram, Fig. 57, represents a ver- 
tical section at the same station, showing the proportion of 
water at different temperatures. Fig. 58 gives for comparison 
the proportion of water at different temperatures at Station I. 
Between Teneriffe and Sombrero three series of temperature 
observations were taken by Lieutenant Bethell with Mr. Sie- 
mens’s resistance deep-sea thermometer; and there seems to be 
little doubt, from the general correspondence of the results with 
those of the protector thermometers, that the instrument an- 
swers its purpose. In some of the observations, however, there 
were wide discrepancies ; but these may have been due to want 
of practice in observing. 
Should it turn out that Mr. Siemens’s instrument can be thor- 
oughly depended upon to give accurate results, it will undoubt- 
edly be invaluable for certain purposes. In our antarctic 
cruise, for instance, on several occasions the surface layer was 
colder than any layer beneath: our thermometers on the Miller- 
Casella construction registered accordingly their minimum on 
the surface; a warmer layer succeeded, in which they regis- 
tered their maximum: but after fixing these two points they 
were useless. A workable instrument on Mr. Siemens’s prin- 
ciple would have given us the bottom temperature, which we 
most of all desired. 
I must say, however, that I doubt if this resistance apparatus 
