614 
ME. J. PRESTWICK ON SUBMARINE TEMPERATURES. 
law dependent on the maximum density of water, which he supposed to be alike in 
fresh and salt water; and he consequently assumed that a temperature of about 4°-4 C. 
(40° F.) prevailed below a certain depth in open seas*, and that in both hemispheres 
there was in certain latitudes a zone from the surface downwards of like uniform 
temperature f. 
On the other hand, we have seen that in 1836-39 Du Petit-Thouars fully confirmed 
the observations of Lenz, that a temperature of from 35° to 37° existed at depths in both 
the great oceans. Arago, in commenting on these results, testifies to their accuracy 
and importance, and remarks that “ the observations collected by the ‘ Venus ’ will 
occupy a distinguished place, on account of their number and exactness, and of the 
great depths at which they were taken.” He also observes that, low as some of the 
readings are, yet all errors must be positive, and that they place on reliable grounds the 
great fact of the prevalence of the same low temperatures at depths in the Pacific as 
well as in the Atlantic, and in the equatorial regions of both oceans ; and he especially 
dwells on the circumstance that they tend effectually to disprove the hypothesis which 
had been advanced, that at great depths there existed a uniform and common tempe- 
rature of 40°F.$ 
It appears, nevertheless, that so little was known of what had already been done and 
written, that Sir James Ross fell into the very same errors as D’Urville had made 
thirteen years before. Unfortunately in this case his conclusions were accepted without 
examination by distinguished writers in two popular works on Physical Geography, and 
obtained a currency for which it is difficult to account §. Although Sir James Ross’s 
experiments were in themselves valuable, they required both detail and corroboration, 
and his conclusions were evidently based on an assumption for which there was no 
warrant. And yet, while his important and positive facts as to the persistence of life to 
great depths failed to receive the attention they deserved, his physical fallacies were 
received almost without a question. As with his predecessor, D’Urville, Sir James 
found in his more numerous and deeper observations that the unprotected thermometer 
commonly marked a temperature of and about 39° to 40 ° ; and taking the maximum 
density of fresh water to be 39°-5, he applied the same reasoning to the open seas as had 
already been applied to freshwater lakes, and assumed, exactly as D’Urville had done, 
that a uniform temperature of about 39°*5 prevailed at depths varying with the latitude, 
and that a belt of water of that temperature, extending from the surface downwards, 
encircles the globe between the 50th and 60th degrees of south latitude, or, as he more 
definitely fixes it, in a mean latitude of about 56° 26' S. [( 
* Yoyage, p. 62. f Ibid. p. 59. 
} “ II faut done esperer que le fameux nombre +4 0, 4 si etourdiment emprunte aux observations a la surface 
et au fond des lacs d’eau douce de Suisse cessera de paraitre dans les dissertations ex prof esso, comme la limite 
au-dessous de laquelle la temperature du fond des mers ne saurait jamais descendre.” (Yoyage de ‘La Yenus,’ 
Physique, vol. v. p. 22 ; and ‘ (Euvres Completes,’ vol. ix. p. 254.) 
§ I may, however, remark that their mention of the subject is incidental, and confined merely to giving the 
facts on Ross’s authority. 
|| “It is therefore evident that about this parallel of latitude there is a belt or circle round the earth, 
