OF THE MICROSCOPE. 45 



Mounting Microscope," from the fact that it may be folded 

 together so as to occupy very little space, and may then be 

 packed in the case which contains the compound microscope, 

 or carried in its own little box. It is capable of receiving 

 lenses of long focus, as the rod which carries the horizontal 

 arm slides up and down in a tube upon which a rack is cut. 

 This sliding movement serves for a coarse adjustment, the rack 

 and pinion just mentioned serving for the fine adjustment. 

 The mirror is hung with all necessary movements, and the arm 

 which carries the lenses is provided with the Society screw, so 

 that ordinary achromatic objectives may be used thus saving 

 the expense of extra lenses. 



The engraving fails to show an important feature which is 

 provided by the makers. This is a joint in the arm, which, in 

 connection with the rotation that may be given to the rod to 

 which the arm is attached, enables the operator to place the 

 lens over any part of the preparation. We call this an im- 

 portant feature, for we hold it to be essential to the convenient 

 use of the dissecting microscope that the preparation should 

 remain stationary and firm during the processes and operations 

 to which it is subjected. This is just the reverse of what is 

 found to be most convenient and efficient in the compound 

 microscope. There the objective should be immoveable (hori- 

 zontally), and the object should be adjusted to a proper posi- 

 tion in relation to it. 



Rests for the arms, when using the dissecting microscope, are 

 easily improvised out of books or blocks of wood. \Ve prefer, 

 to anything else, good-sized blocks of wood, having the form of 

 a wedge with the point cut off. They are clumsy, it is true, 

 but very comfortable. Small rests may be fitted like wings to 

 each side of the stage, and these are furnished at a slight extra 

 cost by the makers of the microscope just described. 



Cheaper forms of this microscope are also made. In these 

 the instrument is not made to fold up, and there are a few 

 other points (not essential to the efficiency of the microscope) 

 in which expense is avoided. But as improvements are being 

 constantly introduced, those who require a good dissecting 

 microscope should procure the catalogues of all the various 

 dealsrs before they decide. 



