HAEMONIC AInTALYSIS AND PKEDICTION OF TIDES. 127 



any desired position by tightening up on the clamp screw, which, 

 pressing against the small spring at the back, forces the crank-pin 

 block outward against the flanges of the groove with sufficient pres- 

 sure to prevent any slipping. A milled head wrench B is used for 

 tightening the clamp screw. A small rectangular block e of hard- 

 ened steel is fitted to turn freely upon the finely polished axle of the 

 crank pin. This block is designed to fit into and slide along the slot 

 of the component frame. 



Positive and negative direction. — ^All the component shafts and 

 cranks may be grouped into two ranges — those above the medial 

 horizontal plane of the framework being in the upper range and those 

 below this plane in the lower range. In the following discussion 

 direction toward this medial plane is to be considered as negative 

 and direction away from the plane as positive; that is to say, lor all 

 components in the upper range the positive direction will be upward 

 and the negative direction downward, while for the components 

 in the lower range the positive direction will be downward and the 

 negative direction upward. 



Component dials. — To indicate the angular positions of the com- 

 ponent shafts, the pointer (a, fig. 21) moves around a dial (4^, fig. 

 16) which is graduated in degrees. These dials are fastened to the 

 frame of the machine back of the component cranks on both sides, 

 of the machine, those on the time side being graduated clockwise 

 and those on the height side counterclockwise. These dials and 

 pointers are so arranged that the angular position of a component 

 shaft at any time will be the same whether read from the dial on the 

 height side or from the dial on the time side of the machine, and at 

 the zero reading for any component the height crank will be in a 

 positive vertical position and the corresponding time crank in a 

 horizontal position. At a reading of 90° the height crank will be 

 horizontal and the time crank in a negative vertical position. 



With the face of the machine registering the initial epoch, such as 

 January 1, hour, of any year, the value of t then being taken as 

 zero, each component shaft may be set, by means of its releasable 

 gear, so that the dial readings will be equal to the a of the corre- 

 sponding component as represented in formulas (472) and (473). 

 If the machine is then put in operation, the dial readings will, for 

 successive values of t, continuously correspond to the angles (at + a) 

 of the formulas, as the gearing already described will provide for the 

 increment at. 



Component sliding frames. — *For each component crank there is 

 a light steel frame (42, fig. 16) fitted to slide vertically in grooves in 

 a pair of angle pieces attached to the side plates of the machine. At 

 the top of the component frame there is a horizontal slot in which 

 the crank pin slides. As the machine is operated the rotation of 

 the component shafts with their cranks cause each crank pin to move 

 in the circumference of a circle, the radius of which depends upon the 

 setting of the pin on the crank. This motion of the pin, acting in 

 the horizontal slot of the component frame, imparts a vertical har- 

 monic motion to that frame. The frame is in its zero position when 

 the center horizontal line of the slot intersects the axis of the com- 

 ponent shaft; positive motion is the direction away from the medial 

 horizontal plane of the machine and negative motion is toward the 

 medial plane. The displacement of each component height frame 



