72 H. J. Grayson : 



The glass slab carried, in addition to the screw and its bearings, 

 a long rectangular bar — also of glass — lying parallel to the screw, 

 and serving as a guide and support for the extension lever bar of 

 the nut, in a position identical with that occupied by the same 

 parts upon the ruling machine when in action. Hence the nut 

 could be traversed from end to end of the screw, without the 

 slightest movement in rotation. A second long rectangular bar — 

 In this case of machined iron lying parallel to the screw, but about 

 6 inches from it, was also secured to the base plate. This iron bar 

 served mainly as a guide for a smaller bar or block of iron sup- 

 porting a small travelling microscope which could l^e moved in a 

 direct line from end to end of the screw. The microscope was fitted 

 with an objective and ej-e-piece, affording a combined magnifica- 

 tion of al:»out 25 diameters; tlie eye-piece being fitted with a 

 micrometer scale having 100 scale divisions within the field of view. 

 The V bearings supporting the screw were both exactly of the same 

 dimensions and height, and one of them was provided with a thrust 

 plate enabling the screAv to be rotated without end play. For con- 

 venience in rotation, and recording of positions, the other end of 

 the screw was fitted with a simple graduated disc and short lever 

 handle. 



The swivelling steel ring surrounding the nut carried a carefully 

 made parallel plate of quartz about U in. long by | in. in width, 

 and thick enough to prevent flexure. One face of this plate was 

 cemented to the steel ring in a horizontal position, while its outer 

 face, which was optically true and polished, could be brought 

 to a position strictly in alignment with the travel of the nut, and 

 therefore of the screw axis, an essential condition for this method 

 of testing. 



This agreement Avas arrived at by trial and error, the quartz 

 plate being adjusted so that a longitudinal movement without 

 rotation of the screw in the V bearings caused no change in the 

 position of the indicator (described below) as seen in the micro- 

 scope. 



To complete the testing equipment, a delicately sensitive lever 

 indicator was constructed. This was provided with adjustable 

 bearings and a needle index bar with a magnification ratio of about 

 1 to 20, Avith respect to its length and fulcrum adjustment; or with 

 the microscope a combined magnification of 500 diameters. The 

 index point of the needle moved in a vertical plane across the 

 scale of the miscroscope eye-piece, and was adjusted, when in use, to 



