24 Rev. Mr. Emmet t on [Jan. 



all the analyses of the native phosphates and avseniates that we 

 possess, from which it follows that a metal may give with each 

 of those two acids no less than eleven different salts. Mine- 

 ralogy presents us with nine different modes of combination, and 

 the remaining two are very common in our laboratories. 



In an old memoir on a particular species of tantalite from 

 Finland, the specific gravity of which much exceeded that of the 

 other species, and whose powder had a bright cinnamon colour, 

 I had determined it to be a tantaliuret of iron (not oxidated) 

 mixed with a small portion of tantaliate of oxidulous iron. The 

 new experiments which I have lately made on tantalium prove 

 that what I formerly considered as metallic tantalium, is in fact 

 an oxide of that metal which I have since learnt how to reduce 

 completely. We thus have two tantalites in Finland, one of 

 which is the neutral tantahte of the protoxides of iron and 

 manganese, and the other a compound of the protoxide of iron 

 and protoxide of tantalium. 



M. Mosander has been engaged in the analysis of the white 

 serpentine, which we discovered at Gullsjo, on our visit to that 

 place. You will find the formula in the systematic enumeration. 

 This stone contains besides a little strontita. 



M. Walmstedt has communicated to the Academy of Sciences 

 a long work on Peridot ; from which it follows that the formula 



■ Ml 



IS ,. > S. He found no lime in that mineral. 



Article VI. 



Oti finding the Longitude at Sea. By the Rev. J. B. Emmett. 



(To the Editors of the Annals ofFJiilosophy.) 



GENTLEMEN, Great Ou.teburn, A"oi>. 23, 1825. 



On account of the importance of the subject, various expe- 

 dients have been devised. Of those which are perfectly just in 

 theory, few can be employed on account of the peculiar circum- 

 stances in which the mariner is placed. Notwithstanding the 

 number of plans that have been adopted, and the great excel- 

 lency of many of them, the problem has been but imperfectly 

 solved, and perh?,ps no very great improvement can be expected. 

 However, whatever tends to increase the accuracy of the 

 methods now in use, or to facilitate their application, must be 

 considered important both in a scientific and commercial point 

 of view. 



The lunar method, although less accurate than some others, is 

 that on which the mariner must chiefly rely ; it is used in our 

 navy, and on board the East India ships ; it gives good practical 



