608 
ME. J. PRESTWICK ON SUBMARINE TEMPERATURES. 
stream forms, as is well known, a trough of warm water, from below which the cold 
water rises up as a wall in approaching the coast. 
Captain Maury has given* incidentally a few deep-sea temperatures made by the 
U. S/Coast Survey (Dunsterville, Brooke, and Rodgers) during the few years previous 
to the publication of his work ; but it is a subject which he does not treat so fully as other 
points of ocean physics. It is not stated what instruments were employed. 
On the voyage of H.M.S. 4 Cyclops’ in 1857, forty-one important observations were 
made by Captain Pullen in the North and South Atlantic, Indian Ocean, and Red Sea, at 
depths of from 2400 to about 16,000 feetf. It was on this voyage that the first regular 
precautions against pressure were taken in this country. Captain Pullen was furnished, 
by order of the late Admiral FitzRoy, with some instruments constructed purposely for 
deep-sea observations, the object of which was explained in the following memorandum, 
communicated to me by Captain Pullen : — 
“ In Six’s self-registering thermometer, the long bulb, filled with spirits of wine, is so 
delicate, that under a great pressure of ocean it is more or less compressed, and drives 
the spirit against the mercury, which is thus acted on not only by temperature, but by 
the mechanical pressure of sea-water. 
“ With a view to obviate this failing, Messrs. Negretti and Zambra undertook to 
make a case for a we&k bulb, which should transmit temperature, but resist pressure. 
“ Accordingly a tube of thick glass is sealed outside of the delicate bulb, between 
which and the casing is a space all round, which is nearly filled with mercury. 
“ The small space not so filled is a vacuum, into which the mercury can be expanded, 
or forced, by heat or mechanical compression, without doing injury to, or even com- 
pressing, the inner and much more delicate bulb. 
“This provision is meant to guard against possible compression of even the outer 
glass, strong as it is. 
“ One may ask, Why not strengthen the inner tube, the bulb, at once, so as to be 
equal in power of resistance to the outer casing ? Mr. Glaisher and the makers say 
no ; the bulb will yield a little, on account of its length, be it even as strong as the 
outer case. (Signed) “ Robert FitzRoy, Admiral. 
“May 19th, 1857.” 
With these instruments Captain Pullen made a series of observations, and was the 
first in this country to confirm the observations of the continental observers that so low 
a temperature as 35° existed in the depths of intertropical seas. In reply to my inquiries, 
Captain Pullen informs me that, after comparing the deep-sea thermometers with 
standards kept on deck and setting the indices, “ they were placed in copper cylinders, 
* The Physical Geography of the Sea. By M. T. Maury, LL.D., U.S.N., 11th edit. London, 1857, pp. 
53, 261, 263, and Appendix, p. 351. The last edition of 1874 gives no new facts. 
t Twelve of these are given in Proc. Roy. Soc. vol. ix. p. 189, and the others are abstracts from 
Captain Puuleej’s MS. Journal, of which he has kindly given me the particulars ; to these latter “ u” is attached 
in the Tables. 
