22 PRACTICAL TREATISE ON 



the stage entirely free and open by taking away the legs, 

 applying a fine threaded screw to regulate and adjust its 

 motions, and adding a concave speculum for objects that are 

 opaque." This microscope was made entirely of brass, and 

 was fastened to the top of a box, by a scroU or bracket, 

 from which rose two flattened pillars, one having a horizontal 

 arm, was made to sHde up and down against the other, 

 and carried the compound body, the coarse adjustment of 

 which was effected by this movement, but the fine, by a 

 screw two inches in length, fixed to the back of one of the 

 pillars, and when its nut was seciu*ed by a screw, which 

 clamped the sliding piUar, then the body could be moved 

 slowly up and down. The stage, somewhat of the shape 

 of a cross, had several holes in it, for the reception of 

 the condensing lens, forceps, and fish-pan. The lower part 

 of the compound body was cylindrical for the space of two 

 or more inches, and marked with numbers corresponding to 

 those of the lenses, upon this, a Lieberkuhn with a long 

 tube was made to slide, and when set to the figures there 

 marked, an object placed on the stage would be in its focus. 

 In the year 1747, Mr. Cuff invented a micrometer for this 

 instrument; it was made of a lattice of fine silver wires, distant 

 from each other one-fiftieth part of an inch, intersecting at 

 right angles, and so placed in the focus of the eye-glass, as to 

 divide the whole visible area of the microscope into squares, 

 whose sides were each one-fiftieth of an inch. The microscope 

 of Benjamin Martin, described in a work published at Reading 

 in 1746, was of the compound form, and adapted for being 

 carried in the pocket ; it was of a cylindrical shape, like the 

 body of Culpeper's, and, like it, the adjustment was made by 

 sliding one tube within the other, the mirror was placed in 

 the bottom of the tube in an inclined position, and was not 

 capable of being moved. It was also supphed with a screw 

 micrometer of a peculiar construction, which had, on the out- 

 side of the body, a dial-plate and hand resembhng the face 

 of a watch. To this ingenious optician we are indebted for 

 the invention of the hand magnifier, with one or more lenses, 

 which has undergone little or no change since his time. We 



