1825.] Temperature oj the Surface Water of the Atlantic, 333. 



He thus disposes of the mineral in question. "Dr. Brewster has 

 observed that in certain varieties (of apophyUite) to which he has 

 given the name of Tesselite^ the phenomena of double refraction 

 cannot be explained upon the supposition ofa single axis, and even 

 the properties of the mineral are not uniform in this respect through- 

 out the whole mass, but that it appears to be composed of 

 various parts acting differently upon light. It will depend upon 

 2i future accurate examination of the crystalline forms and other 

 properties of this substance in comparison with these observa- 

 tions, whether they will concur in fixing the limits of the species, 

 or whether this will depend solely upon the optical structure of the 

 mineral 



Thus ihefate of my lucubrations* on the structure of apophyl- 

 lite, which, it will be recollected, went to show that the optical 

 characters of minerals were not yet sutticiently understood to be 

 relied upon for the discrimination of species, is their distinct 

 recognition by one of the best mineralogists of the present day. 



H. J. B. 



Article IV. 



Notice on the Temperature of the Surface Water of the Atlantic , 

 observed during a Voyage to and from Jamaica. By H. T. 

 De la Beche, Esq. FRS. &c. 



(To the Editors of the Annals of Philosophy.) 



GENTLEMEN, 



My principal object in presenting the annexed notice of tem- 

 peratures for insertion in the Annals is to induce some of the many 

 persons who so often traverse the Atlantic to and from our West In- 

 dian Colonies, to make similar observations (than which nothing 

 can be more easy) respecting the temperature of the surface water 

 during their voyages, as we can only arrive at any thing like a 

 satisfactory theory on this subject from accumulated observa- 

 tions, made at different seasons of the year, and in various parts 

 of the Ocean. 



The following observations were made at noon each day, the 

 temperature of the surface water being found by plunging a 

 thermometer into a bucket of water just taken from the sea, and 

 that of the air being ascertained on deck, and in the shade. 



Currents must of course have considerable influence on the 

 temperature of the surface water, for instance, it seems probable 

 that the continuation of the Gulf Stream raises the temperature 

 to the southward of the Great Bank of Newfoundland. 



As it is not, however, my present object to enter more fully 



