DESCRIPTION OF PLATES. xxxv 



PLATE XXXI. 



Fig. 453, 454. The appearance of the star Lyra, viewed with telescopes magnify- 

 ing 460 and 6450 times respectively. From Dr. Herschel. P. 390. 



Fig. 455. The appearance of the nebula in Orion, about half a degree in length. 

 From Messier.* P. 391. 



Fig. 456 . . 463. The appearances of different nebulae. From Dr. Herschel. 

 P. 391. 



Fig. 464. A section of the nebula to which the sun is supposed to belong, its 

 projection forming the milky way ; taken in a plane perpendicular to its longest 

 diameter. From Dr. Herschel. The large star in the middle represents the sun, 

 and the circle drawn round it is at forty times the distance of the nearest fixed stars, 

 comprehending probably all the stars which are visible to the naked eye. P. 362. 



Fig. 465. A large spot, traced through different forms in its path across the sun. 

 From Dr. Wilson. A is its place 23 Nov. 1769 ; B, 24 Nov. ; C, 11 Dec. ; D, 

 12 Dec. ; and E, 17 Dec. P. 399. 



Fig. 466. A, a large spot on the sun ; B, the arrangement of the luminous and 

 opaque strata of clouds by which Dr. Herschel explains the appearance of the spot. 

 P. 399. 



Fig. 467. A, a spot with a lighter portion in the middle ; B, the arrangement of 

 the strata corresponding to it. P. 399. 



Fig. 468. The position assumed by the strata which had formed the spot shown in 

 the last figure, viewed about an hour afterwards. P. 399. 



Fig. 469. A and B are the forms of a solar spot, at about two hours' distance of 

 time ; C, D, and E, are the successive forms of another spot. P. 399. 



Fig. 470. The appearance of the zodiacal light, or solar atmosphere, as it is seen 

 in these climates, in the evening, about the beginning of March ; A B being the 

 horizon, and C the supposed place of the sun. P. 400. 



PLATE XXXII. 



Fig. 471. A representing the sun, B the earth, and C the planet Mars ; suppos- 

 ing Mars and the earth to set out together from D and E, the angle D A C was 

 determined by Kepler from calculation, and the angles BAD and A B C by observa- 

 tion ; whence it was easy to construct the triangle ABC, and to find the proportion 

 of A B to AC. P. 402. 



Fig. 472. The solar system, representing the form and proportions of the orbits 

 of all the primary planets, and of three of the comets. The parts of the orbits 

 represented by entire lines are on the north of the ecliptic, the dotted parts on the 

 south : the letters A and P denote the aphelion and perihelion. The point in the 

 centre, which ought to be only ^ of an inch in diameter, represents the sun. The 

 figures of the respective planets show their comparative magnitude, that of the sun 

 being represented by the innermost of the graduated circles which inclose the whole : 

 they are placed according to their actual situations on the 14th June, 1806. The 

 letters M D show the mean distance of the comet of 1759, being placed at the 

 extremity of the lesser axis of the ellipsis in which it must be supposed to revolve. 

 P. 408. 



Fig. 473. The periodical times of the different planets, represented by lines of 

 different lengths. P. 408. 



Fig. 474. The comparative velocities of the different planets, represented bylines 

 which show the number of English miles described in a second, on the scale marked 

 on the lowest line. P. 408. 



Fig. 475. The places of the ascending nodes of all the planets, marked on one 

 half of the ecliptic, supposed to be extended in a straight line ; together with the 

 inclinations of their orbits. The line marked F. F. E. E, shows the situation of the 

 fixed ecliptic. P. 408. 





Hist, et Mem. 1771, p. 458. 



