MEMORANDA. 201 
Substitute for the Rack-and-Pinion movement of Microscopes.— 
I have found the following application of the “ frictional 
gearing” (sometimes used in cotton-spimning machinery) 
answer perfectly well in lieu of the ordimary rack-and-pinion 
movement of the body and stage of microscopes. It is quite 
free from the unpleasant drop consequent upon a worn rack 
and pinion, and is exceedingly strong, it beg impossible to 
injure or fracture the movement, by any undue violence, in 
turning the milled head, for beyond a certain amount of strain 
it will slip. 
Fig. 1 is a plan and fig. 2 side view of a microscope body 
with this movement attached. The same letters of reference 
apply to both figures ; a is the body of an ordinary microscope; 
6 a strip of brass in the position of the usual rack—this is 
planed out longitudinally into three or four angular furrows, 
slightly truncated, as shown; c is a turned cylinder of steel 
with milled heads, in place of the pinion—this has furrows and 

Fig. 1. Fig. 2. 
grooves of the same angle exactly corresponding with those of 
the strip. 
The pinion or roller is pressed into the strip by means of 
a hammered brass spring (d), which serves to ensure a uniform 
pressure, needful to obtain sufficient bite between the roller 
and strip, to overcome the resistance of the work, and also 
gives accommodation to any irregularities of construction. 
The lifting power or bite depends upon the acuteness of the 
angle given to the ridges and furrows, which must not be too 
obtuse, or not exceeding 30°. 
I have made a friction rack of this description which works 
very smoothly, and lifts a weight of 16 lbs. without slipping ; 
this force is amply sufficient for most optical purposes.—F. 
H. Wenuam. . 
