HARMOlSriC AISTALYSIS AND PREDICTIOE^ OF TIDES. 123 



machine No. 2, which is described in the following section. A 

 description of the machine is also given in Special Publication No. 32 

 of the U. S. Coast and Geodetic Survey. 



34. U. S. COAST AND GEODETIC SURVEY TIDE-PREDICTING MACHINE NO. 2. 



The Coast and Geodetic Survey tide-predicting machine No. 2 

 was designed to sum simultaneously the terms of formulas (472) and 

 (473) and to register the successive heights of the tide (h) by a dial 

 and pointer as well as graphically by a curve, and also to indicate 

 the time or values of (t) which satisfy equation (473) for the high and 

 low waters. This machine was designed and constructed in the ofB.ce 

 of the U. S. Coast and Geodetic Survey. Designed in 1895, its con- 

 struction was begun the following year, and after some interruptions 

 it was completed in 1910. It was first used in makiaig predictions 

 for the U. S. Coast and Geodetic Survey Tide Tables for the year 1912 

 -and has been used for all editions of the Tide Tables since that time. 



The general appearance of the machine is illustrated by Figures 

 12, 13, and 14. It is about 11 feet long, 2 feet wide, and 6 feet high, 

 and weighs approximately 2,500 pounds. The principal features 

 are: First, the supporting framework; second, a system of gearing by 

 means of which shafts representing the different components are 

 made to rotate with angular speeds proportional to the actual speeds 

 of the components; third, a system of cranks and sliding frames for 

 obtaining harmonic motion ; fourth, summation chains connecting the 

 individual component elements, by means of which the sums of the 

 h.armonic terms of formulas (472) and (473) are transmitted to the 

 recording devices ; fifth, a system of dials and pointers for indicating 

 in a convenient manner the height of the tide for successive instants 

 of time and also the time of the high and low waters ; sixth, a tide 

 curve or graphic representation of the tide automatically constructed 

 by the machine. The machine is designed to take account of the 

 37 components listed in Table 3, including 32 short-period and 5 long- 

 period components. 



The heavy cast-iron base of the machine, which includes the 

 operator's desk, has an extreme length of 11 feet and is 2 feet wide. 

 This forms a very substantial foundation for the superstructure, 

 increasing its stability and thereby diminishing errors that might 

 result from a lack of rigidity in the fixed parts. On the left side of 

 the desk is located the hand crank for applying the power (1, fig. 12), 

 and under the desk are the primary gears for setting in motion the 

 various parts of the machine. 



The superstructure is in three sections, each consisting of parallel 

 hard-rolled brass plates held from 6 to 7 inches apart by brass bolts. 

 Between these plates are located the shafts and gears that govern the 

 motion of the different parts of the machine. 



The front section, or dial case, rests upon the desk facing the oper- 

 ator and contains the apparatus for indicating and registering the 

 results obtained by the machine. The middle section rests upon a 

 depression in the base and contains the mechanism for the harmonic 

 motions for the principal components Mj, Sj, K^, Oj, N^, and M^. 

 The rear section contains the mechanism for the harmonic motions 

 for the remaining 31 components for which the machine provides. 



72934— 24t 9 



