34 THE AMERICAN MONTHLY [Mar 



plate a smooth touch and prevents the edges from getting 

 nicked. A slantwise grinding will put a slight bevel on 

 the harsh edges. The final grinding is done by holding 

 the glass perpendicularly while rubbing over the stone. 

 The edges are smoothed on a finer grained stone without 

 sand. 



The four pieces are then ready to be put together. Gret 

 a small quantity of liquid glue, to which a little chalk, 

 clay or tripoli, has been added to make it pasty. It will 

 dry speedily, say in a few hours, while simple glue might 

 not harden for several days. Place a small circular spot 

 of the glue an inch wide at each of the four corners of the 

 larger plate, a little away from the edges. Adjust the 

 next two larger pieces of glass accurately to the upper 

 outer corners of the under plate. TWs done, the inch 

 wide glass carrier piece is placed between them, and 

 carefully adjusted for parallelism, and sliding contact 

 free from latteral play. The plate is then set aside for 

 the glue to fully set and to lose every indication of shift- 

 ing under side pressure. The inch-wide sliding piece 

 may now be removed for the addition of the slide or slip 

 holder frame. This is made by taking a piece of stiff 

 pasteboard a little thicker than an average glass alip, and 

 superposing on it a 1 x 3 slip, and cutting through the 

 cardboard so that the slip will drop into it snugly. Out- 

 side of this space the pasteboard carrier frame may be ^ 

 inch wide all around. This pasteboard skeleton is glued 

 squarely across the middle of the glass carrier piece. 

 This completes the slide carrier and the glass stage plate. 

 With the slide carrier in use, a 1-6 objective ofi'ers an 

 air clearance space for the slide to pass freely, to and fro. 



It is useful to locate on the upper surface of the left 

 half or side of the plate, a reference line to continuous- 

 ly bisect the center of the field of view of a 1-6 objective. 

 To calibrate this line, and indicate it on the glass plate, 

 the glass plate is laid squarely on the metal stage of the 



