610 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



shoulders h, rising from a common base plate. On one side the axis 

 carries a quadrant turning with the Microscope, and having one 

 arm parallel with the optic axis of the Microscope. A plumb line 

 gives the angle on the quadrant. On the other side of the axis is 

 a screw-nut to clamp it in any desired position. The brass base plate 

 to which the shoulders Ti are attached, slides by means of a screw Mj^ 

 in a second piece shown in the figure. The motion is at right angles 

 to the plane of incidence of the light falling on the object, i. e. from 

 right to left (or vice versa) as the observer would stand in using the 

 instrument. The second piece is again part of another slide, which 



Fig. 92. 



is moved backwards and forwards by the screw Mg ; the motion here 

 is at right angles to that of the first slide, and therefore parallel to 

 the plane of incidence. The extent of these two movements is read 

 off on two millimetre scales on the guides of the slides, and the 

 screw heads are divided for reading fractional parts of mm. The 

 heavy iron base G of the whole instrument rests upon three feet, 

 and the plane and convex glasses g are laid upon a small stage T 

 attached to the front of the instrument, and capable of being raised 

 and lowered above G as required. 



