126 - Experiments on the Solar and on the 



When the volume of a fab fiance is increafed by heat, cah 

 any thing be conceived more eafily practicable, in many 

 cafes, than to determine, by actual rrieafurement, the pro- 

 portion that the increafe bears to the volume of the mafs at 

 a given lower temperature? Is not this already done in many 

 cafes } The experiments on this point mould be multiplied, 

 fo as to embrace, if poflible, every known fubtlance and 

 every degree of heat. Moil fubftances would then become 

 their own thermometers : nay, all are fo at prcfent, but we 

 have not examined the relations of all their different fcales. 

 [To be continued.-] 



VI. Experiments on the Solar and on the Terre/lrial, Rays that 

 occa/ion Heat ; -with a comparative View of the Eaivs to 

 •which Light and Heat, or rather the Rays ivhich occajion 

 them,, are fubjeel, in order to determine whether they are the 

 fame, or different. By William Hkkschel, LL.D. 

 F.R.S. 



[Continued from Page 21.] 



$th Experiment. Refleclion of the Heat of a Coal Fire by a 

 plain Mirror. 



I 



placed a fmall fpeculum, fuch as I ufe with inv 7-feet 

 reflettors, upon a (land, and fo as to make an angle of 45 

 decrees with the front of it*. This was afterwards to face 

 the fire in my parlour chimney, and would make the fame 

 ansrle with the bars of the crate. At a diftance of ■?!- 

 inches from the fpeculnm, on the reflecting fide of it, was 

 placed the thermometer No. 1 j and clofe by it, but out of 

 the reach of the reflected rays, the thermometer No. 4. The 

 whole was guarded in front, againft the influence of the fire, 

 bv an oaken board 1 ! inch thick, which had a' circular open- 

 ing of i| inch diameter, oppofite the fitnation of the plain 

 mirror, in order to permit the fire to fliine upon it. The 

 thermometers were divided from the mirror by a wooden 

 partition, which alfo had an opening in it, that the reflected 



* See Plate J I. fig. 2. 



rays 



