58 E. M. NELSON ON A HYDROSTATIC FINE ADJUSTMENT. 



scope with a bar movement, Fig. 2 as adapted for the " Jackson 

 Lister " form, and Fig. 3 as adapted for the continental model, or 

 11 student's ' microscope. In Fig. 1 there are shown two iron 

 chambers (a, a) connected together by a transverse pipe and filled 

 with mercury ; one of these chambers is provided with a plunger 

 (b), the other chamber being similarly provided with a ram (c). The 

 fine adjustment screw is intended to act on the plunger, and the 

 ram on a stud carried by the nose-piece of the microscope, the stud 

 being pressed against the ram by means of a spring. 



In Fig. 2, the plunger (b) and ram (c) are both fitted to one 

 chamber (a), so as to permit of its being used on the Jackson 

 Lister model, and the fine adjustment screw may, in this case, 

 be placed so as to act on the plunger on either side, or at the 

 back of the instrument. 



In Fig. 3, the plunger and ram are fitted to opposite ends of the 

 chamber (a), in order to adapt the apparatus to the continental 

 model. The application of the apparatus to this form of micro- 

 scope would, in my opinion, be especially useful, and would mate- 

 rially increase its efficiency, for, as the fine adjustment is at present 

 constructed, it precludes the possibility of fine and accurate patho- 

 logical work being done with the instrument. 



As shown in the Figs., the ram has a sectional area four times 

 greater than that of the plunger ; therefore the movements of the 

 fine adjustment screw would be reduced in the proportion of one to 

 four ; but it is obvious that, by varying the relative diameters of 

 the plunger and the ram, the ratio may be varied almost indefi- 

 nitely, as, for example, a plunger of 1^ inch and a ram of ^ inch 

 would give a ratio of one to thirty-six, so that one turn of a 

 screw having fifty threads to the inch would only impart a move- 

 ment of xgVg- of an inch to the object-glass. 



