194 ^^' ''"* NATURE OF HEAT, 



prefented ; tlic other, which had not been blackened, re- 

 maining in its tirft pofition, at tiie diHance of two inches. 

 The other coat- Other limilar experiments were made to (hew whether 

 acSlelJated the thofe coatings or clothings which, in the former experiments 

 cooling, were alfa with the large vefl'els, had accelerated their cooling, did alto 

 thHadTation." '^ ^"^"^^^^"^ ^^^''" P^^^'" of radiation, as (hewn by the procefs and 

 inftruments laft defcribed. And the refalts invariably proved 

 that this is the cafe. 



It was alfo a queftion deferving to be inveftigated, whether 

 any peculiarity belonging to the metallic furface hitherto ufed, 

 namely of brafs, might have influenced the refults. 

 Exp. 14, 15. Exp. 1 4, 1 5. The two large cylindrical veflels No. 1 and 2, 

 faces radiate " ^^'^''^ covered with a lingle coating of oil varnilh, and on this, 

 equally, \viien fufficicntly dry, was laid a covering of thick gold leaf 



upon No. I, and thick filver leaf on No. 2. Thefe veflcis 

 were cooled through the interval of 10 degrees, in the fame 

 time as the naked vefTel ufed as the ftandard. Similar expe- 

 riments with vefi'els of tinned iron and of lead, (liewed that 

 the radiation from all thefe metals, though fo different in theif 

 conducing power, is the fame. 



'* Is not this," fays the Count, " owing to their being all 

 equally wanting in tranfparency r And does not this afford us 

 a ftrong prefumption that heat is, in all cafes, excited and 

 communicated by means of radiations or undulations, as I 

 fliould rather choofe to call them ?" 



And he proceeds to obferve, that another very important 

 queftion alfo muft be decided before thefe points can be deter- 

 mined, and that is. Whether bodies are cooled in confequence 

 of the rays they emit, or by thofe they receive ? The celebrated 

 experiment of Piflet has (hewn, in our author's opinion, that 

 rays or emanations proceed/rowi cold bodies, which may be con- 

 centrated by concave mirrors, and will affedt a delicate air 

 thermometer, 

 Exp. 16, 17. Exp. Id, 17. The horizontal cylindrical veffels (Fig, 5, 



A cold body dc- p/^g /^ of the prefent volume) were made very clean and 

 pcraure o^f other bright, were duly fixed, and left for feveral hours in a room 

 bodies by radia- j^gar the thermofcope ; and when each veff^l was in fuccetlion 

 Metal horizon- -prefented to that inftrument, with every precaution to pre- 

 tally placed, vent irregularity from external circumftancGs, it was not found 

 to be affcdcd by them. One of the veffels was now taken 

 away and filled with ice and water, and then prefented, at th^ 



> diftance 



