26 UNITED STATES COAST AND GEODETIC SURVEY. 



means of a spur gear, 30 teeth, 48 pitch, mounted on it, through one 

 of 100 teeth to a horizontal shaft running in brackets fastened to the 

 back of the dial case. A pair of bevel gears, 75 teeth each, 48 pitch, 

 connect the latter to that carrying the height pointer on the dial 

 face (plate 7). The height scale is 12.74 inches in diameter or very 

 nearly 40 inches in circumference; so that, with the ratio of gears 

 employed, 1 inch of chain motion produces 1 inch of motion of the 

 pointer at the scale. 



Ileiglit scales. — Three height scales are provided, graduated to* 10, 

 20, and 40 feet and tenths, respectively. For predicting the smaller 

 tides, the amplitudes are set up in the machine to four times their 

 value and the 10-foot scale is used. For tides of average ranges the 

 amplitudes are doubled and the 20-foot scale is put in place, while the 

 larger tides are set up at their true amplitudes and read off the 40- 

 foot scale, the one in place when the photograph was taken. The 

 turning of a small button at the top of the scale permits of quick 

 removal and accurate replacement of a scale. The pointer can be 

 released and clamped in the desired position by means of a small 

 milled nut at its center. 



The height amplitudes and the epochs having been set for a station 

 and the machine being set in motion, the pointer indicates the height 

 of the sea at any time, shown on the day, hour, and minute dials. 



Time chain. — The time chain is fastened at the rear end of the 

 right side of the machine, as seen from the desk, in the same 

 manner as the height chain (plate 6). It is passed under and 

 over all the time pullej^s of the rear and front component frames. 

 Leaving the last one of these, it passes down around an idler pulley at 

 the base, forward under the desk, around another idler pulley fastened 

 to the base frame, upward, its flat side making a quarter turn, through 

 the desk top into the dial case, over a third idler pulley across the 

 dial case immediately behind a horizontal opening in its front plate 

 (plate 7), exposing it to plain view of the operator. It passes around 

 the thread grooves and ends at the side of a pulley wliich, with its 

 shaft threaded pulley for a counterpoise and lateral screw motion, 

 is an exact counterpart of the height sum pulley and its mounting 

 (plate 9). The weight of the counterpoise, which rises and falls under 

 the desk, and the motion of which is reduced to one-half by a movable 

 pulley, is 18 ounces, one-fourth of which, or 4 J ounces, is effective 

 in keeping the chain taut. The length of the time chain from the 

 fixed end to the platinum zero link is 27 feet 1 inch and the total 

 length 30 feet 7i inches. 



When all the time amplitudes are set to zero, a link in the chain, 

 made of platinum with a point projecting upward, is adjusted by 

 means of the nuts at the fixed end of the chain, to be in exact coin- 

 cidence and contact with a fixed index, also of platinum, in the middle 



