130 U. S. COAST AND GEODETIC SURVEY. 



the free end of the chain must be twice as great as that in the pulley. 

 The scale of the pulley motion is one-half inch to the unit, and there- 

 fore the scale of the chain motion is 1 inch to the unit, and one com- 

 plete rotation of the summation wheel represents a change of 12 units. 



The zero position of the height summation wheel is indicated by 

 the conjunction of an index line (50, fig. 16) on the arm attached to 

 the wheel and an index line (SI, fig. 16) on a bracket attached to the 

 framework of the machine just below the summation wheel, the 

 wheel itself being approximately one-half filled with the summation 

 chain. The length of the chain is adjusted so that the summation 

 wheel will be in its zero position when all the component frames are 

 in their zero positions. It will be noted that the conjunction of the 

 index lines will not alone determine the zero position of the wheel, 

 since such conjunctions will occur at each turn of the wheel, while 

 there is only one zero position, which is that taken when the com- 

 ponent frames are set at zero. 



The zero position of the time summation wheel is indicated by the 

 conjunction of an index point (11, fig. 12) attached to the time sum- 

 mation chain and a fixed index (12, fig. 12) in the middle of the hori- 

 zontal opening near the bottom of the dial case, and the length of 

 the time summation chain is so adjusted that this conjunction will 

 occur when all of time component frames are in their zero positions. 



Predicted heights of the tide. — When the machine is in operation, the 

 sum of all the cosine terms of formula (472) included in the settings 

 for a station will be transmitted through the height summation wheel 

 to the face of the machine and there indicated in two ways — first by 

 a pointer moving over a circular height scale (8, fig. 12) and second 

 by the ordinates of a tide curve that is automatically traced on a 

 roll of paper (15, fig. 12) . The motion of the height summation wheel 

 is transmitted by a gear ratio of 30 : 100 to a horizontal shaft which 

 is located just back of the dial case. One complete rotation of this 

 shaft represents 40 units in the height of the tide. From- this shaft 

 the motion is carried by two separate systems of gearing to the height 

 pointer on the face of the machine and to the pen that traces the 

 tide curve. 



Height scale. — The height pointer is geared to make one complete 

 revolution for a change of 40 units in the height of the tide. A 

 height scale, with its circumference divided into 40 equal parts and 

 each of these unit parts subdivided into tenths, provides for the direct 

 registering of the sum of the cosine terms of formula (472) as com- 

 municated through the summation wheel. This scale has its zero' 

 graduation at the top and is graduated positively to the right and 

 negatively to the left. The height pointer can easily be adjusted to 

 any position by means of a small milled nut (iO,fig. 12) at the end of 

 its shaft. If it should be desired to refer the predicted heights to mean 

 sea level, this pointer must be adjusted to read zero at the same time 

 that the summation wheel is in its zero position; but if it is desired 

 to refer to some other datum, the pointer will be adjusted according 

 to the elevation of mean sea level above this datum. For the value 

 of h in formula (472) the pointer will be adjusted to a reading corre- 

 sponding to the adopted value of ^o at the time the summation 

 wheel is in its zero position, then this value of Ho will be automatically 

 included with the sum of the cosine terms of that formula. As the 



