130 U. S. COAST AND GEODETIC SURVEY 
columns as would give gear speeds approximating as closely as possible 
with the theoretical speeds of the constituents. By comparing the 
gear speeds as obtained with the corresponding theoretical speeds it 
will be noted that the accumulated errors of the gears for an entire 
dial year for all the constituents are negligible in the prediction of 
the tides. 
368. Releasable gears.—Releasable gears (52, fig. 27) on the main ver- 
tical shafts permit the independent adjustment of the time indicators 
and individual crankshafts. The details of these gears are illustrated 
in figure 30. 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. 
{Tt has sunk into its upper surface a recess a, which is filled by the 
flange of collar B. When in place, the latter isprevented from turning 
iby 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 
wrench (56, fig. 28) is used for setting these gears. Each of the three 
main driving shafts is provided with a clamp (54, fig. 28) to secure the 
shaft from turning when the nut of the releasable gear is being loosened 
or tightened. 
369. Constituent cranks.—Secured to the ends of the constituent 
erank shafts, which projects through the brass plates on both sides of 
the machine, are brass cranks (40, fig. 25) which are provided for the 
constituent amplitudes. Those on the left or height side of the 
machine are designated as the constituent height cranks and are 
used for the coefficients of the cosine terms of formula (458), and 
those on the right or time side of the machine are designated as the 
constituent time cranks and are used for the coefficients of the sine 
terms of formula (459). The time crank on each constituent crank 
shaft is attached 90° in advance (in the direction of rotation) of the 
height crank on the same shaft. For the constituents Sa and Ssa no 
time cranks are provided, as the coefficients of the sine terms corres- 
ponding to these constituents are too small to be taken into account. 
The direction of rotation of each constituent crank shaft with its con- 
stituent cranks is clockwise when viewed from the time side of the 
machine and counterclockwise when viewed from the height side. 
The details of a constituent crank are shown in figure 31. 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 b 
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 f. 
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 unclamped 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 any de- 
sired position by tightening up on the clamp screw, which, pressing 
