TIDE-PKEDICTING MACHINE NO. 2. 19 



components driven from this vertical shaft, Ssa and Mm at the top, 

 and Sa, Msf, and Mf at the bottom, receive their motion from 

 releasable bevel gears to bevel gears on horizontal intermediate shafts, 

 -^ inch diameter, by worm screws at their inner ends, J- inch diame- 

 ter, 13 threads per inch, to worm wheels, 48 pitch, on shafts carrying 

 spur gears 48 pitch, to intermediate sliding spur gears on stud shaft 

 to spur gears on component shafts. The intermediate sUding gears 

 are provided for disconnecting the component shafts from the slow- 

 moving worm-screw gears, thus permitting of more rapid setting of 

 the epochs. 



All the component shafts in the rear component frame are -f^ inch 

 diameter, and all the bevel gears are of 48 pitch and 0.20 inch face. 



Durability of hearings. — The intermediate shafts in both the com- 

 ponent frames run in bracket bearings made of hard cast brass, 

 secured to one of the plates of the component frame. They can 

 readily be replaced, one at a time, should looseness due to wear 

 require their renewal, without putting the machine out of use. 

 Should wear become too great in the bearings of the component 

 shafts, however, which are in the place of the frames themselves, 

 considerable time and expense would be required to repair the 

 machine. For this reason the bearings in the plates were bushed 

 or lined with hard cast-iron rings, forced into place and riveted. 

 It is thought that 50 years' constant use will not cause sufficient 

 wear to require the renewal of the bushings. 



The vertical shafts also run in bracket bearings made of hard cast 

 brass, the one in the front component frame being supported by seven 

 (plate 10), that in the front of the rear frame by six (plate 11), and the 

 rear one (plate 12) by five such bearings. One of the bearings near 

 the middle of each vertical shaft is fitted with a clamping device, 

 consisting of a double-armed steel block fitting over the bracket 

 bearing, with a powerful hexagon-headed steel screw. By means of 

 a large milled-head wrench the screw can be tightened and the shaft 

 clamped so firmly as to prevent its moving under the stresses incident 

 to the loosening and tightening of the releasing gears. The number 

 of teeth in each of the gears conveying motion from the vertical 

 shafts to the component shafts depend upon the speeds of the 

 components. 



Speeds of components. — The speeds of the components are their 

 angular motions expressed in degrees per mean solar hour. They are 

 derived from astronomical data, and were first determined by a com- 

 mittee of the British association, appointed in 1872, ^^for the exami- 

 nation of the question of Harmonic Analysis of Tidal Observations,'' 

 Sir William Thomson being chairman of the committee. Sir George H. 

 Darwin, having taken charge of this work some time later, extended 

 and perfected the fist of components, which was finally pubhshed in 



