4 02 5. /. SHAND 



{efgh) to take German slides (48x28 mm.). Two small spring 

 clips (not shown in the figure) serve to prevent any slight movement 

 of the glass. In order to allow of measurements being made in 

 two perpendicular directions across a rock section, four short pins 

 are inserted in the sides of sledge A ; these make it possible to fix 

 a German-sized slide in cross position upon the micrometer, but 

 the English slides are too long to permit this. 



The attachment of the outermost sledge C to the stage of the 

 microscope is effected by means of runners with beveled edges which 

 fit into grooves in the sides of the stage. One runner is fixed 

 directly to the under surface of the sledge, the other is attached by 

 a simple wire spring to a fixed cross-bar on the under surface of 

 the sledge. This simple arrangement could be replaced, if desired, 

 by a mechanical movement; in any case it would be an advantage 

 to have an additional screw (V, Figs. 1, 2) by means of which the 

 instrument could be clamped to the stage in any desired position. 

 My instrument was made to fit the stage of an "Allan Dick" 

 microscope (Swift & Son), but it is obviously adaptable to any 

 microscope with a rectangular stage. It could even be adapted 

 to a circular stage by means of a rectangular plate clamped 

 temporarily on top of the stage. 



The instrument, as actually made for me, differs in some minor 

 points from the drawings. For instance, the micrometer screws 

 are not rigidly connected to the sledges A and B, as the drawing 

 suggests, but are attached by simple backlash springs which can 

 be seen in the photographs (Figs. 4, 5). The dimensions of the 

 side- and end-pieces of the sledges were slightly increased for the 

 sake of greater strength. The figures relating to these parts are as 

 follows : 



Length of sledge A, S5 mm. 



Width of sledge A (including bevel), 37 mm. 



Travel of sledge A, 16 mm. (this might be increased). 



Length of sledge B, 108 mm. (this might be increased). 



Width of sledge (including bevel), 45 mm. 



Travel of sledge B, 35 mm. 



Length of sledge C, 127 mm. 



Width of sledge C, 54 mm. (might be reduced to 52). 



Thickness of material throughout, 3.5 mm. 



