793 



PLATE. XXXVIII. 



Fig. 510. A scale of tlic heiglit of different parts of 

 the earth's surface above tlie level of the sea, in 

 English feet and miles, and in French toises. P. .574. 



Fig. ."iSO. A. Tiie dotted ellipsis shows the section 

 of a spheroid, which would be the form of the earth 

 and sea if it wcro always in a state of equilihriuni with 

 the attraction of a distant body, and the shaded ellip- 

 sis the actual form assumed in consequence of its ro- 

 tation round its centre, the depth of tlie sea being less 

 than l.*; miles. B. The surface of the sphere being 

 supposed to be flattened, and the tides spread on it, 

 they wo\rld 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 surface beiijg re- 

 gulated by that of the dotted line at B, nearly agree- 

 ing with it in direction, as at D, when the lake is nar- 

 row and deep, but differing from it, as at E, when sha.- 

 lower. P. 579. 



Fig. 521. The progress of the tides from the At- 

 lantic through the channels surrounding the British 

 islands, the lunar tides happening in any part of the 

 shaded lines nearly at the hour, after the moon's south- 

 ing, which is indicated by the figure annexed to it. 

 P. 582. 



Fig. 522. The lines AB and,BC, repreeentingithe 

 heights of the lunar and solar tides, find the angle 

 ABC twice their angular distance, or A DC being 

 simply the angular distance, the line A ;C shows, the 



height of the compsand tide, and the angles B A C and 

 A C B its distance from the lunar and solar tides re- 

 spectively. P. 585. 



F'ig. 523. Tlie two unequal tides represented by the 

 elevation of the ellipsis above the smaller circle may 

 be considered as composed of two equal tides cut off 

 by the dotted circle, and the single tide between the 

 two circles; as the tides B and C make the unequal 

 rides at D, P. 587. 



Fig. 521. The first and second curves represeni 

 two equal semidiurnal and one diurnal tide, whicL 

 would make together two unequal tides : the third and 

 fourth the same tides six hours more advanced : and 

 when these are combined, the first and third destroy 

 each other, hut the second and fourth together com- 

 pose the fifth, or a large diurnal tide. P. 587. 



Fig. 525. A tlie ancient system of the world, 

 adopted by Ptolemy. B th^ arrangement supposed 

 Lv some other astronomers. P. 590. 



Fig. 526. The Egyptian system of the world. P. 

 590. 



Fig. 527. The system of the Pythagoreans, and of 

 Copernicus. P; 592. 



Fig. 528. The mode of representing the inequalities 

 of the celestial motions employed by Ptolemy, the 

 small circle being carried round the circumference of 

 the larger, while the lumiuary revolves in it, so as to 

 diescribe the dotted curve. P. 595. 



Fig. 529. The Tychonic system of the world. P. 

 597. ■ 



