1022 SUMMARY OF CURRENT RESEARCHES RELATING TO 



for the reception of the two principal parts, the socket with the 

 Microscoi)e-tube ami the Btago with the mirror. These parts, with the 

 objective and eye-piece, are contained in a box 12 cm. long and 6 cm. 

 wide and deep (fig. IGi), which can bo carried in the pocket or slung 

 across the shoulder by a strap. 



The body-tube (115 mm. long) slides by hand in the socket for 

 focusing, but,the author suggests replacing this by the ordinary rack-and- 

 pinion arrangement. The socket (iG mm. long) is attached by means of a 

 short arm to a brass piece 19 mm. broad and GO mm. long, which reaches 

 down to the top of the stage. Through this piece passes a broad-headed 

 screw, by which the socket is firmly screwed to the metal plate on the 

 stick. A pin above and below the screw fitting into cori'esponding holes 

 in the metal plate helps to keep the socket firmly in position. The stage 

 with the mirror is fastened to the metal plate in a similar way. The 

 mirror is only arranged for direct illumination, but is movable in all 

 directions, so that the handle of the stick can never interfere with 

 the observation. In the figure the stage-opening is represented by 

 mistake as rather too large, so that a diaphragm would bo necessary if it 

 were desired to use somewhat high powers. A stage-opening of only 

 2 to 3 mm. is found to be most suitable for all purposes, and renders 

 diaphragms unnecessary unless a specially low power is used. 



Pritchard's Microscope with "Continental" Fine-adjustment. — An 

 early form of achromatic Microscope is shown in fig. 1G5, which, from 

 several points of its construction, we have ventured to assign to the lato 

 Antlrew Pritchard, and which is interesting from the peculiarity of the 

 fine-adjustment. 



The spiral spring encircling the stem, in combination with the 

 arrangement of the fine-adjustment screw below, would seem to indicate 

 that what is generally known as one of the earliest forms of the " Con- 

 tinental " fine-adjustment was very soon adopted in England, if, indeed, 

 its construction here did not precede G. Oberhiiuser's, to whom the 

 origination has been generally attributed. It is obvious that, if the 

 spiral spring were sheathed by a tube, the fine-adjustment would be the 

 " Continental " pure and simple. 



The rectangular motions of the stage, actuated in diagonal directions 

 on either side of the stem, are similar in design to those shown in one of 

 A. Eoss's earliest Microscopes figured in the 7th edition of the ' Ency- 

 clopjedia Britannica,' and shown in fig. 16G from an extant example, a 

 form which was also issued under Pritchard's name. 



The condenser beneath the stage, with its long tube mounting, in 

 the continuation of which the mirror is placed, reminds one of the tube 

 with sliding condenser and mirror below, which formed an accessory to 

 many of the earlier Pritchard and Koss Microscopes, and which was 

 in fact a modification of Wollaston's doublet Microscope. 



Griffith's Fine-adjustment. — Mr. E. H. Griffith sends us the fol- 

 lowing description of his new fine-adjustment. In fig. 1G7, 1, 2, 3 repre- 

 sent the milled head, pinion-axis, and pinion of the ordinary method of 

 coarse-adjustment. The milled-head (1) is countersunk on its inner side, 

 and the small wheel (4) is made to exactly fit the countersunk space, 

 the inner surface of (1) and of the wheel (4) being perfectly smooth 

 and flat. Attached to (i) is the socket and pinion (7), all of which are 

 perfectly fitted over the pinion axis (2) between the pinion (7) and milled 



