u 



The Microscope. 



in the grooves, all the field is necessarily brought into view. 

 The cut here printed to show this device is not very satisfactory. 



The object is not as transparent as represented, and it should 

 cover the whole field. The figure represents the first plate I had 

 made, which was screwed on the microscope stage; afterwards it 

 was found simpler to detach the stage and cut the grooves in 

 that directly. The work was done by the Johnson Electric Ser- 

 vice Co., of Milwaukee, Mr. Johnson devising a special tool to 

 cut the grooves and ribs, for these latter are not merely strips 

 soldered on, but they have to be cut to triangular shape and 

 made to fit and accurately correspond to the grooves, so that the 

 motion may be smooth and uniform. I began with one rib, but 

 found two necessary to insure steady motion. When first taken 

 in hand by one accustomed to quick work, the lifting of the 

 frame from one groove to the next seems a little awkward, but 

 after a day or two of work with it this inconvenience is not 

 noticed. I had the first one made October 12, and gradually 

 had the instruments of all of my seventeen assistants thus 

 changed at their request and expense. The alteration costs only 

 $3.00 for each instrument where many are done at once. It 

 would, of course, be more if a separate stage and frame had to be 

 made. The advantages of the device are highly appreciated by 

 all my assistants; they not only have the sense of perfect surety 

 of having covered all the field in their search, but of not having 



