384 INVERTED MICROSCOPE. 



Many little additional conveniences will suggest themselves 

 to almost all microscopists who may use this instrument; but 

 the great principle belonging to it is what I desire to make 

 public, and any other adjuncts that may be described are such 

 as belong to all forms of microscopes. 



NEW FORM OF EYE-PIECE MICROMETER FOR MEASURING OBJECTS 

 UNDER THE MICROSCOPE. 



Facility of measuring objects under the microscope is a 

 great desideratum; and for this reason I now make known 

 what I have been using for this purpose for upward of two 

 years, as it furnishes all that can be desired. The eye-piece 

 micrometer ordinarily in use consists of a glass with divisions 

 drawn in it, contained in a special eye-piece adapted for its 

 use; and whenever the measurement of an object is required 

 we replace the eye-piece used by the micrometer eye-piece, 

 and move the object on the stage, so that its image falls on 

 the marking of the micrometer. With all its advantages this 

 form has many inconveniences, among which I will mention the 

 necessity of using an eye-piece, which is not always the best 

 for examination, the constant interposition of the micrometer 

 in the field of observation, and the necessity of moving the 

 object so as to superpose its image on the micrometer. 



The eye-piece micrometer of Mr. George Jackson, described 

 in Quekett's work on the Microscope, is an improvement on 

 the one just mentioned, but does not do away with all the 

 objections. 



By the present arrangement the micrometer can be used 

 with any eye-piece; it can be withdrawn at pleasure, and 

 placed over the image of the object without regard to its 

 position in the field; for this purpose the tube of the micro- 

 scope is in two parts. G and N (fig. 2) ; the former has a collar h, 

 and projects a couple of inches into 1ST, turns freely in it, and 

 is retained by a small screw n passing through N, and playing 

 on a groove in G. On the upper part of G- there is a small 

 rectangular opening in a little mechanical arrangement, as 

 seen in m. The various eye-pieces are so mounted that when 

 placed in the tube G the planes of their foci correspond with 

 the opening at g, and at the same time there is an opening in 

 their mounting, which is made to come opposite to that of g. 



