22 UNITED STATES COAST AND GEODETIC SUKVEY. 



The horizontal distance between each two component shafts was, 

 of course, fixed by the diameter of the chain pulleys, which was taken 

 as 2 inches, measured upon the center of the chain. 



Harmonic motion of pulleys. — The several views of the sides of the 

 machine show plainly that provision was made for simple harmonic 

 motion of all the chain pulleys and in what manner this was done. 

 The frames with rectilinear horizonital slots 0.24 inch wide were cut 

 from sheet steel ^ inch thick, and drilled and filed out to shapes ren- 

 dering them light, without impairing their rigidity. They move in 

 grooves planed into the inner sides of hard brass angle pieces, which 

 are screwed to the side plates. 



Component cranlcs. — The lengths of the component cranks, depend- 

 ing upon the height unit adopted for the machine and the maximum 

 amplitude of each component, were made ample, in order to provide 

 for any extreme case. They are given in the last two columns of 

 Table C. 



The component cranks are situated immediately behind these frames, 

 their hubs serving as shoulders of the component shafts to which 

 they are securely pinned. The cranks (see adjoining illustration, plate 

 13, fig. h) are of hard brass and have ± slots, a, milled through them, 

 into which are fitted accurately the heads of the steel crank pins, h. 

 The latter are bored out and threaded to receive the square-headed 

 clamp screws, c, by means of which the crank pins can be fixed firmly 

 in any position upon the cranks. A thin slightly curved plate of 

 hardened steel, d, between the head of the crank pin and the bottom 

 of the ± slot, protects the latter from being bruised by the clamp 

 screw and acts as a spring which prevents the crank pin from falling 

 when released. Upon the crank pin, which is 0.19 inch diameter, 

 and finely polished, turns freely a closely fitting rectangular block of 

 hardened steel, e, which fits accurately into and slides along the slot 

 of the steel frame. The milled head wrench for loosening and tight- 

 ening the clamp screw c is at B. 



Upon the side of each crank at its center is mounted a steel pointer, 

 for setting the epoch of the component upon a silvered degree circle 

 screwed to the side plate. The time crank is set upon the shaft 90° 

 ahead of the height crank, and the circles are numbered and the 

 pointers placed so that the effects upon the height chain vary as the 

 cosines of the angles indicated by the pointer, and those upon the time 

 chain as the sines of the same angles. For greater convenience and 

 to avoid errors in setting, the circles of the upper and lower ranges 

 of components were numbered alike and the pointers set upon the 

 crank so that, facing them, all the height circles have their zeros at 

 the right side, the numbering increasing counter clockwise. When 

 facing the time circles, the numbering increases clockwise from the 

 zeros at the tops of all the circles. 



