DESCRIPTION OF PLATES. xli 



Fig. 539. The actual elevation of a portion of water in contact with a hori- 

 zontal surface which is wetted by it. P. 478. 



Fig. 540. The elevation of mercury in contact with a horizontal surface of glass. 

 P. 478. 



Fig. 541. A, a wide drop of water standing on a dry surface, not attracting it. 

 B, a wide drop of mercury, standing on glass. P. 478. 



Fig. 542. A magnified representation of the manner in which the seeds of lico- 

 podium prevent a drop of water from wetting the substance on which it stands. 

 P. 478. 



Fig. 543. The bodies A and B, and the bodies C and D, appear to attract, and E 

 and F to repel each other. P. 479. 



Fig. 544. The apparent cohesion of two plates, between which a fluid is inter- 

 posed. P. 479. 



Fig. 545. The apparent attraction of a drop between two plates, tending to draw 

 it towards the line of their junction, causes the drop to rest in an inclined position 

 of the plates. P. 479. 



Fig. 546. Dr. Herschel's figure, representing by the distance of the curve ABC 

 from the line AC the heat thrown on different parts of AC by a prism, while DC is 

 the illuminated part, divided according to Newton's experiments, the quantity of 

 light being expressed by the distance of the line DEC. P. 490. 



Fig. 547. Dr. Herschel's figure of the distribution of heat and light corrected 

 according to the division of the coloured spectrum, as ascertained by Dr. Wollaston. 

 P. 490. 



Fig. 548. Bernoulli's air thermometer. P. 499. 



Fig. 549. A differential air thermometer, or thermoscope, from which the pres- 

 sure of the atmosphere is excluded. From Kunze. P. 499. 



Fig. 550. A differential thermometer on Mr. Leslie's construction. P. 499. 



Fig. 551. The distribution of the electric fluid in spheres of different sizes, and at 

 different distances, and in a conical point. The density is represented by the dis- 

 tance of the dotted line from the surface. P. 51 1. 





PLATE XL. 



Fig. 552. A. A spark passing between a negative and a neutral ball; B, between 

 a neutral and a positive ball ; C, between a negative and a positive ball. D, two 

 sparks between a negative and a positive cylinder, each of the same form as if it 

 were passing singly from the end of a charged to the side of a neutral cylinder. 

 From Mr. Nicholson. P. 518. 



Fig. 553. A compound galvanic circuit, formed by portions of an acid, pieces of 

 zinc, and wires of silver ; the arrows show the directions of the electric current. 

 P. 522. 



Fig. 554. A compound galvanic circuit, formed by an acid, charcoal and water, 

 the water and acid communicating by a small siphon. P. 522. 



Fig. 555. A compound galvanic circuit, formed by portions of an alkaline sul- 

 furet, and water, and pieces of copper : the liquids being connected by a siphon. 

 Fig. 522. 



Fig. 556. A simple galvanic circuit, formed by wires of zinc and silver, or platina, 

 the lower ends being immersed in an acid, and the upper being brought into contact 

 at pleasure. P. 522. 



Fig. 557. A galvanic battery, in the form of a trough, composed of plates of 

 zinc, silvered on one side, with vacant spaces for the reception of an acid : the letters 

 show the order of the elements, and the arrows the direction of the current, from the 

 positive wire + to the negative wire . P. 523. 



Fig. 558. An electrical machine, on Nairne's construction. A, the cylinder of 

 glass ; B, the cushion, or rubber ; C, the silk flap ; D, the negative conductor ; E, 

 the positive conductor ; F, a ball connected with the internal coating of a glass jar, 

 contained in the conductor. The conductors are insulated by varnished rods of 

 glass. P. 525. 



e 



