BIBLIOGRAPHY OP^ HERSCIIEL's WRITINGS. 573 



Herschel, W.: Synopsis of thk Writings or— Continued. 

 A.. D. Vol. P. 



1800 90 310 i:?tli Experiment. Refraction of the Ileal that aeeompaniea the Coloured 

 part of the Prismatic S2)eetrain. 

 A burning lens 9 iuelies iu diiimeter was covered by a piece of paste- 

 board in which there was an opening of a sufficient size to admit 

 all the coloured part of the prismatic spectrum. As the thermom- 

 eter showed rise of temperature, the conclusions were, that if the 

 coloured rays themselves are not of a heat-making nature, they are 

 at least accompanied with rays that have the power of heating 

 311 bodies, and that these rays are subject to certain laws of refraction 



which cauiHjt differ nnich from those affecting light. 

 311-312 14th Experiment. Refraction of the heat of a Chimney Fire. The 



same burning glass before the clear fire of a large grate. 

 313-314 15th Experiment. Refraction of the Heat of a Red-hot Iron. This 



was by a lens of 1.1 inches diameter. 

 315-31G 16th Experiment. Refraction of lire-heat hy an Instrument resem- 

 hling a Telescope. 



317 17th Experiment. Refraction of the Invisible rays of Solar Heat. The 



burning kus of 9 inches diameter was half covered by a screen of 

 pasteboard, upon which the prismatic spectrum was thrown, keep- 

 ing the last visible red colour one-tenth of an inch from the edge of 

 the pasteboard. The thermometer, which had its ball at the focus 

 for red rays, showed great increase of temperature; but at the same 

 time exhibited a slight red colouration. This occasioned a surmise 

 that possibly the invisible rays of the sun might become visible, if 

 they were properly condensed. 



318 18th Experiment. Trial to render the Invisible Rays of the Sun Visible 



by Condensation. 

 The previous experiment was modified so that the last visible red 

 colour was two tenths of an inch from the margin of the paste- 

 board. Here a marked increase of temperature was evinced with- 

 out a vestige of light. 



319 19th Experiment. Refraction of Invisible Culinary Heat. 



A heated cylinder of iron was placed on one side of a lens of 1.1 inches 

 diameter, and the ball of a thermometer in the secondary focus on 

 the other side of the lens. A small pasteboard screen was alternately 

 removed from before the thermometer and replaced, the thermometer 

 exhibiting corresponding rise and fall of temperature, from a bright 

 red heat of the cylinder down to its weakest state of black heat. 



320-321 20ih Experiment. Confirmation of the l^th. 



322 "As we have now traced the rays which occasion heat, both solar and 

 terrestrial, through all the varieties that were mentioned in the be- 

 ginning of this paper, and have shown that in every state they are 

 subject to the laws of reflection and refraction, it will be easy to per- 

 ceive that I have made good a proof of the first three of my prop- 

 ositions. For the same experiments which have convinced us that, 

 according to our second and third articles, heat is both reflexible 

 and refrangible, establish also its radiant nature, and thus equally 

 prove the first of them." 

 [Dated] Slough, near Windsor, April 2^, 1800. 



323-326 Explanation of the Figures. Plates Xll, Xll, XIV, XV, and XVI. 



1800 90 437 Experiments on the Solar and on the Terrestrial Rays that occasion Heat; 



with a comparative View of the Laics to which Light and Heat, or rather 



the Rays ivhivh occasion them, are subject, in order to determine whether 



