22 DE. A. E. H. TUTTON: 



another. Further, the pair of friction rollers for each plate can be readily adjusted 

 at any distance apart so as to attain the desired theoretical positions for bars of 

 different lengths, for instance either yard or metre bars. The third table for use 

 with end-measure bars as well as line bars will be described in a further communica- 

 tion. It involves novelties of method and of mechanical device which are worthy of 

 separate treatment. 



The Wheel-Control for the Movement of Bands. 



The wheel-control is carried on a very rigid pedestal, x, mounted closely to the left 

 of the interferometer- telescope pedestal, on a slider, X, in a longitudinal dovetailed 

 channel in a large cast-iron plate, Y, which forms the basal table on which the tripod 

 of the telescope pedestal rests. The plate rests directly on the stone pillar d, to 

 which it is firmly bolted down. The slide enables the axis of the wheel to be 

 brought exactly opposite to and in line with the fine-movement endless screw s, 

 which operates the worm-wheel / of the all-important microscope traversing 

 screw. The height of the axis has been approximately adjusted in mounting, and 

 the final small amount necessary to render it accurate is given in the following 

 manner : A stout screw, Z, descends from and is rigid with the axle bearing-bracket 

 U, and passes down freely through the upper looped end of the casting of the two- 

 legged pedestal ; the amount of screw which thus projects down into the loop is 

 regulated by means of a pair of locking nuts, W, which are firmly fixed when the 

 height of the screw, and of the wheel and axle which it carries above, have been 

 adjusted so that the axle is in the same horizontal line with the endless screw s. 



The axial bearing carried at the top of the bracket U is adequately strong and 

 well fitting to prevent all trace of wobble on the part of the wheel, while permitting 

 its easy motion ; the six-inch wheel itself is massive, and very truly balanced, and its 

 face is divided into degrees, an indicating mark being carried on the plate z below the 

 lower limb. Of the three shafts ?/ provided, the author prefers the one. constructed of 

 the new flexible steel shafting, for connecting the wheel with the endless screw s of 

 the microscope fine movement, as it avoids all risk whatsoever of strain. The square 

 continuation of the endless screw fits a correspondingly squared brass socket, fitted 

 with tightening spring, carried by the shaft. The wheel end of the shaft carries no 

 socket, but fits freely into a boring in the wheel axle, where it can be gripped tightly 

 by working a milled nut, J, down the split and tapped end of the bored axle. The 

 second rigid shaft provided fits in a similar manner, with the addition of a telescopic 

 arrangement to enable it to be shortened sufficiently to admit it into the axle boring. 

 A third shaft, also rigid and telescoped, but with the addition of a set of gimbal joints 

 at the endless-screw end, is also provided and fits in a similar manner. The first and 

 the third prove most satisfactory on the whole, being safer as regards possible strain, 

 and the first is used for all purposes of adjustment or demonstration, while the third 

 is employed during actual measurements. The endless screw s, as worked directly by 



