126 U. S. COAST AND GEODETIC STJKVEY. 



to find such values for these columns as would give gear speeds 

 approximating as closely as possible with the theoretical speeds of 

 the components. By comparing the gear speeds as obtained with 

 the correspondmg theoretical speeds it will be noted that the accu- 

 mulated errors of the gears for an entire dial year for all the compo- 

 nents are negligible in the prediction of the tides. 



Releasable gears. — Releasable gears (52, fig. 19) on the main ver- 

 tical shafts of the dial case and component frames permit the inde- 

 pendent adjustment of the time indicators and individual component 

 shafts. The details of these gears are illustrated in Figure 20. A 

 collar C, with a thread at its upper end and a flange at the bottom, 

 is fastened to the shaft by means of three steel screws. The gear 

 wheel A fits closely upon this collar and rests upon the flange. It has 

 sunk into its upper surface a recess a, which is filled by the flange of 

 collar B. When in place, the latter is prevented from turning by a 

 small steel screw reaching into a vertical groove c in the collar C. 

 The lower surface of collar B is slightly dished, and the collar is split 

 twice at right angles nearly to the top. When the milled nut D is 

 screwed down with a small pin wrench, the edge of the collar B is 

 pressed against the edge of the recess a with such force as to make 

 slipping practically impossible. When the nut is loosened, the gear 

 may be turned independently of the main driving shaft. A small 

 wrrench (56, fig. 19) is used for setting these gears. 



Each of the three main driving shafts is provided with a clamp 

 (55, fig. 19) to secure the shaft from turning when the nut of the 

 releasable gear is being loosened or tightened. 



Component era nl's.— -Secured to the ends of the individual compo- 

 nent shafts, which project through the brass plates on both sides of 

 the machme, are brass cranks (4-0, fig. 16) which are provided for the 

 component amplitudes. Those on the left or height side of the' 

 machine are designated as the component height cranks and are 

 used for the coefficients of the cosine terms of formula (472), and 

 those on the right or time side of the machine are designated as the 

 component time cranks and are used for the coefficients of the sine 

 terms of formula (473). The time crank on each component shaft 

 is attached 90° in advance (in the direction of rotation) of the height 

 crank on the same shaft. For the components Sa and Ssa no time 

 cranks are provided, as the coefficients of the sine terms correspond- 

 ing to these components are too small to be taken into account. 

 The direction of rotation of each component shaft with its compo- 

 nent cranks is clockwise when viewed from the time side of the 

 machine and counterclockwise when viewed from the height side. 

 The details of a component crank are shown in Figure 21. The 

 pointer a is rigidly attached to the crank as an index for reading its 

 position on a dial. In each crank there is a longitudinal groove h 

 with flanges in which a crank pin d may be clamped in any desired 

 position. The crank pin has a small rectangular block as a base 

 which is designed to fit the groove in the crank, and through the 

 center of the crank pin. there is a threaded hole for the clamp screw 

 /. Attached to the under side of the crank-pin block is a small 

 spring c that presses the block outward against the flanges of the 

 groove, keeping it from slipping out of place when undamped and 

 at the same time permitting it to be moved along the groove when 

 setting the machine. The crank pin may be securely fastened in 



