56 



Emery comes 

 chiefly from 

 Naxoi. 



It is cheap ; 



not cryftallixed } 



is accompanied 

 by the fame 

 Jubilances as 

 Chinefe dia- 

 mond fpar. 



ON THE rOWKR OF FLUIDS TO CONDUCT HEAT. 



All the emery which is ufed in England, is faid to be brought 

 from the Iflancls of the Archipelago, and principally from 

 Naxos. In thofe places, it is probably very abundant ; as the 

 price of it in London, which I was told was 8 or 10 (hillings 

 the hundred weight, appears little more than fufficient for the 

 charges of carriage. Though I faw a very large quantity in 

 one place, (more than a thouland hundred weight,) I could 

 not find any pieces of a cryftallized form ; poffibly the great 

 proportion of iron ufually mixed with it, may prevent its 

 cryflallization. The whole confifted of angular blocks in- 

 crufted with iron ore, fometimes of an o&aedral form, with 

 pyrites, and very often with mica. The latter frequently 

 penetrates the whole fubftance of the mafs, giving it, when 

 broken, a filvery appearance, if feen in the direction in which 

 the flat furfaces prefent themfelves to the eye. As thefe fub- 

 itances have no chemical relation to the emery itfelf, it is re- 

 markable that they fliould alfo accompany the diamond fpar 

 from China ; for Mr. Klaproth obferves, *\ that its lateral 

 u facets are moftly coated with a firmly-adhering crufl of 

 " micaceous fcales, of a filvery luflre :" he alfo mentions, 

 befides felfpar, pyrites, and grains of magnetic iron ore. 



XL 



Experiments and Obfervations on the Power of Fluids to conducl 

 Heat ; with Reference to Count Rumford's Seventh, EJfay on the 

 fame Subject. By J ohN Dalton*. 



The properties 

 ef heat are con- 

 tinually under 

 our notice. 



Count Rum* 

 ford's experi- 

 ments on the 

 tranfmiflion of 

 heat by circula- 

 tion through 

 flaidSt 



A H E nature and properties of fire or heat are fubjecls 

 which prefent themfelves to our confideration in almoft every 

 department of phyfi.es : it is no wonder therefore that new ex- 

 periments, which point out and define the modes of operation 

 of fire, before unobferved, or at leaft too much overlooked, 

 fhould attract the attention of philofophers. — Thefe obferva- 

 tions were fuggefted upon reading Count Rumford's very in- 

 genious experiments, in his efTay above-mentioned, which ex- 

 hibit a fa6l in a more ftriking point of view than it has ap- 



* Manchefler Memoirs, vol. v. 373, 



peared 



