TIDE-PREDICTING MACHINE NO. 2. 25 



by actual wear. For this purpose it was joined into one endless 

 piece and laid over and under pulleys, some of them only one-half 

 inch in diameter, fastened against the wall of one of the shop rooms, 

 one free pulley being loaded with a 5-pound tension weight, while one 

 of the fixed pulleys was kept immersed in watch oil. By means of a 

 belt from the line shaft the chain was kept in motion during working 

 hours for about a year. 



Height chain. — The height chain is fastened at the rear end of the 

 rear component frame (plate 12). It is riveted to a threaded rod 

 which can be raised or lowered in a bracket, fastened to the plate, by 

 means of two miUed mjts, for purposes of accurate adjustment. 

 From this rod the chain passes under and over all the height pulleys 

 of the rear component frame, by means of two idler pulleys across 

 the space between the rear and front component frames (plate 10), 

 and over and under the height pulleys on the front component frame. 



After leaving the last one of these, the upper — ^ (plate 9), it passes 



down and around the thread groove of the height sum pulley, at the 

 edge of which it ends and is fastened. The circumference of this 

 puUey, as measured on the center of the chain, is exactly 12 inches. 

 It can hold over seven turns of chain, the length of which is cut so 

 that when all the components are set to zero ampUtudes, the thread 

 grooves are half filled and the pulley can either take up or pay out 

 45 inches of chain. The total length of the chain is 27 feet 7 inches. 



The height sum pulley is mounted upon a shaft which runs in bear- 

 ings secured to the plates of the front component frame. By means 

 of a fixed tooth reaching into the threads of a screw fastened to the 

 shaft the latter is forced, when rotating, into a screw motion with a 

 pitch* equal to that of the thread groove of the sum pulley, thus 

 always keeping the chain between the latter and the last component 

 pulley vertical. 



From a threaded pulley secured to this shaft, of a diameter one- 

 half that of the sum pulley, is suspended by means of a silken cord 

 and an idler puUey mounted within and at the top of the component 

 frame, a counterpoise weighing 12 ounces, half of which, or 6 ounces, 

 is effective in keeping taut the chain. 



A pointer at the side of the height sum pulley serves to indicate 

 mean sea level. AH the height amplitudes being set to zero, a fine 

 line at its end is made to coincide with one upon a small bracket 

 immediately below the pulley. 



One end of the chain being fixed, the vertical motion of any one of 

 the pulleys causes double this motion in the free end of the chain, so 

 that the motion of a height pulley through one unit produces a 

 motion of 1 inch at the free end, or one-twelfth revolution of the 

 height sum pulley. The rotary motion of the latter is conveyed by 



