572 BIBLIOGRAPHY OF HERSCIIEL's WRITINGS. 



Herschel, W.: Syxopsis of the Writings of — Continued. 



A. D. Vol. P. 



are subject to tlie laws of reflection. 3. They are also subject to 

 the laws of reflection. 4. They ai'e of difl'erent refraugibility. 5. 

 They are liable to be stopped, in certain proportions, when trans- 

 mitted through diaphanous bodies. G. They are liable to be scat- 

 tered on rough surfaces. 7. They may be supposed, when in a cer- 

 tain state of energy, to have a power of ilJumiuating objects; but 

 this remains to be examined." 



1800 90 297 1st Experiment. Reflection of the Heat of the Sun. 



A thermometer was exposed at the eye end of a ten-feet Newtonian 

 telescope. The rays, after three regular reflections, caused the 

 thermometer to rise 58 degrees. The experiment .cannot ascertain 

 whether these rays were those of light or not. 

 2d Experiment. Reflection of the Heat of a Candle. 

 The ball of a thermometer, placed in the secondary focus of a steel 

 mirror, received 3|^ degrees of heat in five minutes. 



298 3d Experiment. Reflection of the Heat that accompanies the Solar Pris- 



matic colours. 

 The same mirror was covered by a piece of pasteboard, which, through 

 a proper opening, admitted all the visible colors to fall on its pol- 

 ished surfaces, but excluded every other ray of heat that might be 

 either on the violet or on the red side, beyond the spectrum. The 



299 thermometer in the focus rose 35 degrees above its stationary posi- 

 tion in the direct red rays when the mirror was covered. " Thus 

 the prismatic colours, if they are not themselves the heat-maMng 

 rays, are at least accompanied by such as have a power of occasion- 

 ing heat, and are liable to be regularly reflected." 



4th Experiment. Reflection of the Heat of a red-hot Poker. 



300 5th Exjieriment. Reflection of the Heat of a Coal Fireby aplain Mirror. 



301 6th Experiment. Reflection of Fire-heat by a Prism. 



302 7th Experiment. Reflection of Invisible Solar Heat. 



On a board about 4 feet 6 inches long was placed at one end a small 

 plain mirror, and at the other two sensitive thermometers. Upon 

 this board was projected a prismatic spectrum, and just beyond the 

 limit of the red rays the mirror was stationed so as to reflect invis- 

 ible rays to the ball of one of the thermometers. In ten minutes 



303 this thermometer stood four degrees above the other. 



304 8th Experiment. Reflection and Condensation of the Invisible Solar Raya- 

 At the focus of a concave mirror was placed the ball of a thermome. 



ter. Upon the mirror was thrown a i^rismatic spectrum which cov- 

 ered half the mirror. This half was covered by a pasteboard screen 

 80 that only invisible rays were reflected to the baU of the ther- 

 mometer. In one minute the thermometer rose 19 degrees. 



305 9th Experiment. Reflection of Invisible Culinary Heat. 



306-307 10th Experiment. Reflection of the Invisible Rays of Heat of a Polcer, 

 cooled from being red-hot till it could no lonejcr be seen in a dark Place. 



308 11th Experiment. Refraction of Solar Heat. 



The rays from the sun, falling on the mirror of a Newtonian tele- 

 scope 24 inches in diameter, were transmitted after reflection through 

 the four lenses of an eye-piece and allowed to fall on the ball of a 

 thermometer. 



12th Experiment. Refraction of the Heat of a Candle. 



309 The image of a candle flame was thrown upon the ball of a thermom- 



eter by a lens 1.1 in diameter. 



