498 J>, Herschel's Experiments on the solar, and 



that no re-scattering may take place in the thickness of the 

 covering board : the distance of the centre of the holes is 4 

 inches. A little more than an inch below, and under the centre 

 of the holes, are the balls of the small thermometers A and B, 

 well shaded from the direct rays of the sun, by small slips of 

 wood, of the shape of the ball, and of that part of the stem which 

 is exposed. 



Under each thermometer is a small tablet,* on which the ob- 

 jects intended for scattering the sun's rays are to be placed. 

 The tablets are contrived so as to bring the objects perpendi- 

 cularly under the openings, and under the centre of the balls 

 of the thermometers, at the distance of exactly one inch from 

 them. Every thing being thus alike on both sides of the box, 

 it is evident, from the equality of the holes, that an equal num- 

 ber of solar rays will fall on each object, and will by them be 

 scattered back on the thermometers, at equal angles, and equal 

 distances. 



The first five experiments that follow, were made with an 

 apparatus somewhat different from the one here described ; and, 

 though the result of them may not be so accurate as if they had 

 been made with the present one, I must give them as they are, 

 since time will not allow of a repetition. 



195^ Experiment. 



Sun. Message card scattering,' 



o' 64 64 



5 691 66% . . . 5| : s| = ,413 



Here an object of a white colour, 3,6 inches long, and q,6 

 broad, scattered, in 5 minutes, 413 rays of heat back upon one 



* See Plate XXII. Fig. 5. 



