1815.), Explanation of B. Prevost’s Experimenison Dew. 433 
of what has been written by this Gentleman upon them seems to 
me entirely just. But it is nevertheless my opinion, that he could 
not possibly have explained them completely, so long as he was 
ignorant that bodies become colder than the air before they. are 
dewed; a fact, I believe, first known to myself, and not published 
by me until several years after the appearance of his book upon , 
Radiant Heat. | 
I conclude by mentioning very shortly two other things relating 
to Mr. Prevost. The first is, that if he had seen my letter to you, 
which was printed in your Journal last April, he would probably 
have collected from it the information which he now desires. The. 
second, that I feel strongly the commendation, which has been 
bestowed upon my meteorological labours by a person of his high 
rank in philosophy. 
Iam, Sir, your most obedient humble servant, 
London, Nov. 13, 1815. Wirciam CuHaries WELLs. 
4 
ArTICLE XI. 
Memoir on Iridium and Osmium, Metals found in the insoluble 
Residuum of crude Platinum treated by Nitromuriatic Acid, 
By M. Vauquelin.* 
FIRST PART. 
§ I. — History. 
Taovcns what M. Fourcroy and myself have said in the three 
memoirs which we published on the insoluble residue of crude pla- 
tinum treated by the acids has explained most of the principal 
characters of the metals which it contains, and though Mr. Ten- 
“nant, who examined it after us, has added nothing in this respect 
to our knowledge, yet by working upon larger quantities than we 
were able to do at that time, and by increasing the number of ex- 
periments, I have been lucky enough to discover some new pro- 
perties in these metals, to verify some conjectures thrown out in our 
memoirs, and in some cases to correct mistakes into which we had 
fallen. 
I have been at great pains to endeavour to discover simple pro- 
¢esses for obtaining these mictals in a state of purity; for it was 
because one of them had not been obtained in that state that certain 
properties have been ascribed to it which belong only to a mixture 
of it with other matters. 
Finally, 1 have constated, with the greatest certainty, the exist- 
ence of the two metals announced by Mr. Tennant, which Four- 
¢roy and myself had mistaken for modifications of a single species, 
* Translated from the Ann, de Chim, luxxix, 150, Feb, 134. 
Var. VI, N° VI. 2E 
