SCIENTIFIC NEWS. 223 



On the Reflection of obfcure Heat. 



C. Picket's experiment related in his eflay on fire, to prove P'&et's expen- 

 the reflexibility of obfcure heat is well known. It confifts in tii heat w .^ 

 placing oppofite to each other two concave metallic mirrors, mirrors. 

 In the focus of one is placed a hot but not luminous cannon- 

 ball, in the focus of the other a very fenfible air thermometer, 

 and the latter is foon feen to rife rapidly. 



The fame philofopher has fince publifhed fome other experi- 

 ments on the fame fubject. 



Having employed a lighted candle inftead of the cannon- CJafs intercepted 

 ball, he placed between the two foci a plate of very thin clear ^ J 6 * but n< * 

 iranfparent glafs, and which intercepted the light very little : 

 the thermometer indicating the tranfmiflion of heat, flopped 

 that inftant. 



The two mirrors were placed at the diftance of 25 metres Diftance ofmir- 

 {yards) one from the other, in order to determine whether the rors 2 5 metres * 

 time of the propagation of the radiant heat from one focus to 

 the other could be appreciated. A heated but not luminous 

 bali was fufpended at one of the foci, before which a fcreen 

 was placed. At the inftant that this obftacle was removed, the 

 fluid of the thermometer, which was before perfectly at reft, 

 began to move, and no fenfible interval could poffibly be per- 

 ceived between the fuppreffion and the effects of the tranfmitted 

 Jieat. 



C. Piftet relates this experiment in the Bibliotheque Britan»The heat \m 



nique, in fupport of the opinion he had advanced in his efTay J". ftant ty tranX* 



\ if., ,, , r _,. . . . , mitted, 



on fire, that light and heat are not the lame. This opinion has 



iince been renewed by M. Herfchell. — Bulletin des Sciences, 



No. 62. 



On certain FaSls commonly urged againfi tlie Doctrine of two 

 Electric Fluids. % tit* Tk. emery, Engineer of Mines. 

 (Bull, des Sciences, No. 63.) 



Among the facts which have been offered in fupport of The experiment 

 Franklin's hypothefis of a Tingle eleade fluid, the moft re-<£ P^nga 

 markable is the following, (commonly called Lullin's card, Lullin's card. 

 from the inventor of the experiment). 



Having placed between two metallic conductors a card, 

 which touches each of them, by its oppofite faces, in two 



different 



