xl DESCRIPTION OF PLATES. 



angular distance, the line AC shows the height of the compound tide, and the angles 

 B AC and A CB its distance from the lunar and solar tides respectively. P. 448. 



Fig. 523. The 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 tides at D. P. 449. 



Fig. 524. The first and second curves represent two equal semidiurnal and one 

 diurnal tide, which 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, but the second and fourth together compose the fifth, or a 

 large diurnal tide. P. 449. 



Fig. 525. A, the ancient system of the world, adopted by Ptolemy. B, the 

 arrangement supposed by some other astronomers. P. 452. 



Fig. 526. The Egyptian system of the world. P. 452. 



Fig. 527. The system of the Pythagoreans, and of Copernicus. P. 454. 



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 luminary revolves in it, so as to describe the dotted curve. 

 P. 456. 



Fig. 529. The Tychonic system of the world. P. 457. 



PLATE XXXIX. 



Fig. 530. The repulsive force of two particles of matter, situated at the distance 

 A B or A C, is represented by the ordinates or perpendiculars B D, C E, drawn to 

 the curve D E, supposing the force to be inversely as the distance ; but the law of 

 the force appears to be more nearly represented by a curve like F E. The line D FG 

 shows the magnitude of the cohesive force, which overcomes the repulsion at the dis- 

 tance AG, and is balanced by it when the particles arrive at the distance A B or AH. 

 The dotted lines represent the nature of the changes made in the lines FE, DFG, 

 and FH, by an elevation of temperature. P. 474. 



Fig. 531. The general direction of the cohesive force acting on a particle of a 

 liquid at A being represented by A B or AC, that of the repulsive force will be DA 

 or EA, and in order to maintain the equilibrium, the forces BF and CG, making 

 together H A, must be supplied by the pressure or reaction of the internal parts. 

 P. 475. 



Fig. 532. A. The transverse section of a drop, supposed to be of considerable 

 length, and flat at the sides : the curvature of the outline being every where propor- 

 tional to its distance from the horizontal line A B. B, a round drop, the concavity 

 at the horizontal line being equal to the convexity which would be found by cutting 

 off the drop horizontally ; the sum or difference of the curvatures being every where 

 proportional to the distance from this line. P. 476. 



Fig. 533. The solid AB possessing half the attractive power of the liquid CD, 

 the surface of the liquid will remain horizontal : for the attractions will be repre- 

 sented by DA, DE, and DC ; and of these DA and DE make DB, and DB and 

 DC make DF, which is in a vertical direction. If the solid be more attractive, the 

 forces will be combined nearly as at G, and if less attractive, as at H. P. 476. 



Fig. 534. The form of the surface of a liquid in contact with a plane and ver- 

 tical side of a solid which is wetted by it. The height of the ascent of water is about 

 one fourth of that which is here represented. P. 477. 



Fig. 535. The form of the surface of a liquid elevated between two plates which 

 meet at A, and are at a little distance from each other at B ; about one third of an 

 inch, supposing the liquid to be water. P. 477. 



Fig. 536. The height at which water will stand in tubes of the form and magni- 

 tude which are here represented. P. 477. 



Fig. 537. The depression of mercury, in contact with a large or flat glass vessel, 

 is one fourth as great as that which is here represented. P. 478. 



Fig. 538. The depression of mercury within a small tube of glass. P. 478. 



