DESCRIPTION OF PLATES. xxxix 



compared with the excess of the motion of Venus in its orbit above that of the 

 earth. P. 431. 



Fig. 515. A planisphere nearly resembling that of Professor Bode. The outer 

 circle is fixed to the chart, and is divided either according to the degrees of the 

 ecliptic, or the days of the month ; the graduated circle immediately within it is 

 divided into 24 hours, and is fixed to a circle of pasteboard, out of which the circle 

 NE S W, representing the horizon, is cut, the place being filled by thin varnished 

 paper, with circles of azimuth and altitude engraved on it, which it carried round 

 with the hour circle. P. 433. 



Fig. 516. A diagram showing the length of the day, and the time of the sun's 

 rising and setting in any part of the globe, within a few minutes ; the time of the 

 year being found in the graduated circle representing portions of the ecliptic, and the 

 latitude on the middle line, by following the concentric circles of declination till 

 they meet the horizon passing through the given latitude, the line drawn from the 

 pole through this point will cut the equator in the point showing the length of the 

 day or night. Thus, on the first of March, in latitude 50 north, the length of the 

 day appears to be nearly 10 hours and f , whence the sun must rise about 37 minutes 

 after six ; but in latitude 85 the sun never sets on that day. P. 433. 



PLATE XXXVI. 



Fig. 517. Projection of the constellations of the northern hemisphere on the 

 plane of the equator. P. 433. 





PLATE XXXVII. 



Fig. 518. Projection of the southern hemisphere. P. 433. 



PLATE XXXVIII. 



Fig. 519. A scale of the height of different parts of the earth's surface above the 

 level of the sea, in English feet and miles, and in French toises. P. 439. 



Fig. 520. A. The dotted ellipsis shows the section of a spheroid, which would 

 be the form of the earth and sea if it were always in a state of equilibrium with the 

 attraction of a distant body, and the shaded ellipsis the actual form assumed in con- 

 sequence of its rotation round its centre, the depth of the sea being less than 13 miles. 

 B. The surface of the sphere being supposed to be flattened, and the tides spread on 

 it, they would assume the form of the waves here shown. The dotted straight line 

 shows the mean height, which is a little above the surface in the principal sections of 

 the spheroid, although not universally. C. The nature of the tides of lakes, the sur- 

 face being regulated by that of the dotted line at B, nearly agreeing with it in direc- 

 tion, as at D, when the lake is narrow and deep, but differing from it, as at E, when 

 shallower. P. 444. 



Fig. 521. The progress of the tides from the Atlantic through the channels sur- 

 rounding the British islands, the lunar tides happening in any part of the shaded 

 lines nearly at the hour after the moon's southing, which is indicated by the figure 

 annexed to it. P. 446. 



Fig. 522. The lines AB and BC, representing the heights of the lunar and solar 

 tides, and the angle ABC twice their angular distance, or A D C being simply the 



