Experiments on reJleSled Heat, 361 



Befides the foregoing general arrangement, the author gives a previous comparative viewr 

 of fa£ls relating to light and heat as follows : 



I. Light, both folar and terreftrial, is a fenfation occafioned by rays emanating from 

 luminous bodies which have a power of illuminating obje£ls ; and according to circum- 

 ftances of making them appear of various colours. 2. Thefe rays are fubjedt to the laws 

 of refle£tion. 3. And alfo thofe of refraftion. 4. They are of different refrangibility. 

 5. Are liable to be flopped in certain proportions when tranfmitted through diaphanous 

 bodies. 6. And to be fcattered on rough futfaccs. 7. And laftly, they have hitherto been 

 fuppofed to have a power of heating bodies, but this remains to be examined. 



I. Heat, on the other hand as well terreftrial as folar, is a fenfation occafioned by rays 

 emanating from candent fubftances which have a power of heating bodies. Thefe rays 

 have the fame affe£tions as have been enumerated in the 2, 3, 4, 5, and 6th divifions of the 

 laft paragraph, and 7. They may be fuppofed, when in a certain ftate of energy, to have 

 a power of illuminating objedls ; but this remains to be examined. 



The paper before us contains the firft part of the experimental inveftigation of the fubje£\: 

 under the three firft heads. The three next, and a difcufhon which will be breught on by 

 the feventh article, are referved for the fecond part. 



Experiment i. ReJleElion of the heat of the fun. The fun's rays were received In a ten 

 foot Newtonian telefcope, with a camera eye piece, with no ey& glafs. By proper adjuft- 

 ment the focus was made to fall on a fmall thermometer, which was raifed 58 degrees. The 

 rays, therefore, whether of light or not, did occafion heat after three regular reflections. 



Experiment 2. RefeBion of the heat of a Candle. At the dlftance of 29 inches from a 

 candle a fmall fteel mirror, 3, 4 inches diameter, and about 2, 75 inches, focal length, was 

 placed. Two thermometers were di^fpofed, one in the fecondary focus, and the other very 

 near it, but out of the courfe of the reflefted light. In live minutes that in the focus rofe 

 3I degrees, which it loft again in fix minutes when the candle was covered, and again reco- 

 vered it in five minutes when the rays were fufFered to fall on the mirror. The other ther- 

 mometer remained ftationary throughout. 



Experiment 3. RefeStion of the heat that accompanies the folar prifmatic colours. The folar 

 fpeftrum given by a prifm was admitted through pafteboard (which limited the vifible 

 colours) upon the fteel mirror. The thermometer in the focus was raifed 35° in two 

 minutes. 



Experiment 4. RefeBion of the heat of a red hot poker. The mirror was placed at the dlf- 

 tance of 12 inches from a red hot poker, and the thermometer placed in its fecondary focus. 

 A fmall pafteboard fcreen was placed to guard the thermometer from the dire£t heat. In 

 one minute and a half it rofe 381°, and fell 28° in the next minute and a half, when the 

 mirror was covered. 



Experiment 5. RefleSlion of the heat of a coal fire by a plain mirror. A fmall fpeculum 

 (PI. XVI. fig. 1.), fuch as the Dodor ufes with his feven feet rcfledors was placed upon 

 Vk ftand, fo as to make an angle of 45° with the front of it, and confequently with the bars 



Vol.. IV.— ^OVEMBEB. 1800. 3 A - of 



