50 



THE AMERICAN MONTHLY 



[Feb., 



3. Draw a scale each side of the center, at CC ; be- 

 gin one inch from the center, or nearer if you wish. Be 

 sure that both sides are exactly alike. Make the notches 

 1-16 inch apart. Use a very sharp-pointed pair of 

 compasses to mark with, but if you have none, paste a 

 white paper over the top of your table and mark witli a 

 pen and ink. Some prefer the paper. 



To use the device, place a slide upon the table as indi- 



cated by the dotted lines, with two of the corners upon 

 the scale, being' always sure that the opposite corners nre 

 ripially distant from the centre. For example, if the 

 slide measures three inches from one corner to the op- 

 })Osite corner, place the opposite corner at 1^ on tlie 

 scale. Press down the clips firndy, and you are reatly 

 to proceed. 



Be accurate; take a little exti-a time at first until you 

 become accustomed to use it. 



