Fine Adjustments 23 



micrometer screw being released this spring produces the 

 reactionary power. One arm of the lever is four and a half 

 times longer than the other, consequently the weight of the 

 body at the milled-head end of the lever and the motion 

 imparted are reduced in this ratio. Thus the makers give 

 the weight of a body of one of their instruments as 

 17 ounces, and this divided by 4J reduces the resistance 

 to 3J ounces. This system has the advantage that the 



FIG. 5. SECTION OF LIMB OF MICROSCOPE TO SHOW SYSTEM OF FINE 

 ADJUSTMENT. 



position of the milled head on the limb is convenient for 

 manipulation, and is not altered when the body is racked 

 up that is, it is not carried by the rack- work, as in many 

 forms, so that its attachment to a focusing rod of a camera 

 for photo-micrography is easy and convenient. There is 

 also a very simple means of adjustment provided for taking 

 up any slackness through wear. The slide in which the 

 fine adjustment is fitted has sprung slots, to which are 

 fitted screws (shown in Fig. 3, page 19, marked A). By 

 turning these screws slightly, the spring-fitting grips the 



