TIDE-PREDICTING MACHINE NO. 2. 29 



the dial case. At such times the base-line pen is thrown upward, 

 making a mark above the base line, which is a record of the time of 

 the high or low water traced by the curve pen. 



Both this circuit and the one making the hour and day breaks have 

 one battery wire in common, which is led to a small switch at the left 

 side of the desk, just above the crank shaft (plate 8), by means of 

 which the battery can be cut out when the machine is not in operation. 



Curve fen. — The curve pen is mounted in a swiveling arm on a 

 light carriage which slides along two vertical steel rods. The pen, of 

 the ordinary fountain type, is pressed against the paper by a light 

 coil spring under the outer end of the swivel'arm, but can be kept 

 away from the paper by the turning of a small nut. Being fitted 

 with a metal lock joint it can be quickly removed and replaced in 

 exactly the same position. Motion is imparted to the curve pen by 

 the height chain through the height sum pulley in the following 

 manner. 



Scale of the tide curve. — The horizontal shaft running in brackets 

 fastened to the back of the dial case, the lower one seen on plate 4, 

 the rotary motion of which, as before stated, is thirty one-hundredths 

 that of the height sum pulley, carries upon it three sliding change 

 gears of 48 pitch, with 75, 100, and 90 teeth, respectively. Immedi- 

 ately above this shaft is mounted another one with three gears of 75, 

 50, and 60 teeth, respectively, and, at its outer end, a thread grooved 

 pulley with a circumference of 4 inches, measured on the centers of 

 the chain fastened at its side and wound around it (plate 14). From 

 this pulley the chain passes through the dial case around an idler 

 pulley in its front, up past the curve pen carriage over another idler 

 pulley to a counterpoise rising and falling within the dial case. A 

 clamp and clamp screw at the pen carriage permits of the latter being 

 secured to the chain at any desired point. . 



By means of the three different ratios of the change gears a motion 



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



height sum pulley, can be converted into pen motions with either of 



the following values : 



1 30 75 

 With gears 75 :75, or 1 :1, -j^ X Jqq X ;^ X 4=0.1 inch. 



1 SO 90 

 With gears 90 : 60, or 3 : 2, j^ X j^^ X g^ X 4=0.15 inch. 



With gears 100 : 50, or 2 : 1, ^ X ^ X ^ X 4=0.2 inch. 



When the amplitudes set up in the machine are multiplied by four 

 and the 10-foot scale is used, the tide curve may be traced, within the 

 hmits of the height of the sheet, upon scales of 1 to 15, 1 to 20, or 1 to 

 30 of nature; with amplitudes multiplied by two and the use of the 



