CONSTEUCTIOX OF THE APPARATUS. 



55 



Tf different masses acquire in equal times equal velocities, 

 the moving forces are proportional to the masses moved. 



The wheel of the apparatus is useless unless very accurately 

 turned ; the wheel and its frame should therefore be purchased from, 

 an instrument maker. The frame is fastened by three wood screws, 

 with round heads, to a vertical surface, as a door-post, or a wall ; or 

 it may be screwed to a board, l m< 6 long, 12 cm wide, 2 cm thick, into 

 the side of which, at about the height of a table, a strong iron hook 

 is screwed, which serves for clamping the board in a vertical 

 position by the side of the table in the manner shown in fig. 45. 



. 45 (an. f.roj. real size]. 



The board after being screwed perpendicularly to the table may 

 be firmly secured in its position by a small wooden wedge between 

 its lower end and the floor. The divisions may be drawn by means 

 ! of a common bevel-rule, with strong pencil, either upon the board 

 or the wall itself, or upon a strip of stout drawing-paper, of which 

 i the upper end is placed between the frame and the board, and 

 held fast by the frame, while the lower end is fastened by two 

 drawing-pins. 



The weights are made of lead, 2 cm- 5 in diameter. A small hole 

 is bored in the wooden cylinder, round which the paper is rolled, 

 ard a brass or copper wire, about l mm thick, the ends of which are 

 afterwards bent into hooks, is pushed into the hole. To secure it 



