360 Heat ; and the Rays by which it is' eccajloned. 



appear to us to be clear, and deduced immediately from the refults of the experiments. They 

 may therefore tend to the advancement of philofophical chemiftry, and to the perfe£tion of 

 the arts and manufa£lures. We, confequently, recommend to the clafs (of the national 

 inftitute) to order them to be printed in the volumes which it propofes to publilh. We, 

 cannot, however, agree with M. Prouft in fome points, ift. That nickel, cobalt, and 

 manganefe are not precipitated by fulphurated hydrogen. 2. That the black dull, which 

 feparates during the folution of zinc, does not contain carburet of iron. 3d. That zinc is 

 feparated from arfenic by diftillation. The contrary is fo well known by chemifts, that it 

 requires no proof. 



Experiments on the folar and on the ierrejlrial Rays that occafion Heat ; with a comparative 

 View oj the Laws to which Light and Heaty or rather the Rays which occafion them, arefub- 

 je£l, in order to determine whether they are the fame or different. By WitliAsi Herschel, 

 LL.D. F.R.S*. 



JL HE word heat is mod commonly ufed to denote a certain well known fenfation. It is alfo 

 €inployed to Cgnify the caufe of that fen^tion, as well by the vulgar as by men of fcience : 

 fome of whom have added certain diftinftive terms, fuch as latent, abfolute, fenfible, radiant, 

 while others have treated of the matter of heat, and caloric. Dr. Herfchel has not thought 

 fit to adopt any of thefe terms in his Memoir, but has chofen to treat of the rays that occafion 

 heat ; not meaning either to ftate that thefe rays are heat, or the manner in which they pro- 

 duce it. In his prefatory obfervations he alfo in effe£l remarks that his prefent refearch is 

 confined to the agency of heat in its ftate of radiance ; without entering into any confidera- 

 tions refpefting the general nature of heat itfelf, whether it be matter or modification, or 

 of radiance, whether it be the projeftion of particles, the undulation of a fluid, or any other 

 habitude or thing. 



His fubje£l: is reduced to three general heads : the firft relates to the heat of luminous 

 bodies in general as it comes direftly from the fun, or from the terreftrial flames of torches, 

 candles, lamps, blue lights, &c. — the fecond includes the heat of coloured radiants as from 

 the fun, when its rays are feparated by the prifm, or from culinary fires openly expofed ;— « 

 and the third divifion relates to heat obtained from radiants, where neither light nor colour 

 in the rays can be perceived. This is to be had as before {hewnf, directly from the fun, 

 by means of a prifm applied to its rays, and alfo from fires inclofed in ftoves, or from red- 

 hot iron, cooled, till it can no longer be feen in the dark. 



* Abridged from the Phil. Tranf, for j8co, page S93. 

 t Philof. Journal IV. 310. 

 - Befide« 



