TIDE-PREDICTING MACHINE NO. 2. 23 



The components 8a and Ssa have height cranks only, the sine terms 

 of their first derivatives being too small to be taken into account. 



Chain pulleys. — The chain pulleys turn on steel pins 0.18 inch 

 diameter, screwed into steel plates -^ inch thick, H inch wide, and 

 in inch high, which slide in grooves planed into the inner sides 

 of U-shaped hard brass guides, screwed to the sides of the plates. 

 Incidentally these guides serve to unite securely the two halves of 

 the plates forming the rear component frame. The steel plates car- 

 rying the pulleys, or pulley shdes, excepting those of some of the larger 

 components which will be referred to further on, are connected 

 directly with the cross-slot frames by means of steel strips ^^g- inch 

 thick and 0.2 inch wide. 



One side of each pulley guide is widened to accomodate the silvered 

 amplitude scale and its numbering, which is read by means of an 

 index line cut upon a small strip of German silver screwed upon the 

 pulley slide in a manner to permit of its being adjusted accurately to 

 the zero of the scale when the crank is in a horizontal position or the 

 amplitude is set to zero. 



Amplitude scales. — Only the negative halves of the amplitude 

 scales are ruled upon the pulley guides. To set the amplitude, the 

 component shaft is released, the crank set vertical pointing toward 

 its chain pulley; the crank pin is released with the aid of a milled- 

 head wrench and moved up or down until the index on the pulley 

 slide indicates the desired amplitude upon the scale, when the crank 

 pin is again tightened. The unit of the height scales, 0.5 inch, is 

 subdivided to tenths, which permits of setting amplitudes to hun- 

 dredths by estimation. The time-scale unit of each component is the 

 product of the height-scale unit and the ratio of the speed of that 

 component to that of the mean moon, or M^, in accordance with the 

 coefhcient of the derived series. 



The maximum amplitudes of the larger components, upon the 

 scale of 0.5 inch per height unit, require cranks so long that the 

 machine as a whole could not have been kept within dimensions 

 suitable for an ordinary-sized room without special provision. The 

 maximum amplitude for M^, for instance, requires cranks of 10 inches 

 on the height and time sides. To accommodate these components 

 in a reasonable space, two component shafts were provided for M2, 

 82, and K^, and the motions of their respective chain pulleys and those 

 of several other components were doubled by means of racks fastened 

 to the cross-slot frames which gear into the smaller ones of pairs of 

 1 : 2 spur gears, the larger ones engaging into racks fastened to the 

 pulley slides. This reduced the largest of the cranks to 2.5 inches. 

 The racks are 0.2 inches wide, of 40 pitch, and are held in close gearing 

 with the spur gears by flanged rollers which are adjustable for taking 

 up any play due to wear. Counterpoise weights were provided for 



