354 BENJ. PIKE'*, JR., DESCRIPTIVE CATALOGUE. 



Microscopic investigation being now considered indis- 

 pensable in the various scientific researches in anatomy 

 and physiology, important improvements have been effect- 

 ed in the optical and mechanical construction of these in- 

 struments, especially in the adaptation of achromatic 

 object-glasses, by the aid of which alone, delicate struc- 

 tures can be satisfactorily developed ; but which have 

 hitherto been excluded from general use from their very 

 expensive character. Achromatic microscopes can now 

 be supplied with excellent lenses, and all the most ap- 

 proved mechanical arrangements, at a very moderate 

 cost. The author having devoted considerable attention 

 to this branch of his trade, can furnish instruments, the 

 optical and mechanical structure of which will bear com- 

 parison with the most reputed manufacture. 



Ross Confound Achromatic Microscope, No. 1. This 

 instrument (Fig. 788) consists of a brass pillar, about five 

 inches long, screwed into a tripod base ; the upper part 

 of the pillar is a moveable joint, having attached an arm 

 supporting the compound body of the instrument, and a 

 square brass bar upon which slides the stage, which is 

 moveable by a milled head and rack and pinion motion. 

 The stage is a large flat plate with a central opening, and 

 provided with spring clips and other apparatus for hold- 

 ing the objects. Near the lower end of the brass bar is 

 the concave mirror, moveable in various ways, for reflect- 

 ing the light through the centre of the stage upon the 

 object thereon placed. On the under side of the stage is 

 the diaphragm, used for cutting off extraneous light when 

 viewing minute transparent objects ; it consists of a plate 

 of brass perforated with several holes of different sizes ; 

 this revolves on a pivot so as to bring each hole in suc- 

 cession under the object-glass. This microscope has a 

 well-constructed set of eye-glasses, and three achromatic 

 lenses, which may be used together, in pairs or singly, as 

 different degrees of magnifying power are required. 

 By means of the joint the instrument may be turned in a 

 horizontal position, enabling the observer to use the in- 

 strument in some examinations with more ease than when 

 in the vertical position. The instrument when set up is 

 about ten inches high ; is supplied with a dissecting-knife, 

 point, forceps, several test-objects, and slips of glass on 

 which to place objects. The parts may be unscrewed, 



