268 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 



Between the ends of the bar slides an arm carrying a sprung 

 socket, and the arm can be clamped at any given point of the bar. 

 Through the socket is passed a glass cylinder, cemented to a brass 

 collar at the upper end. and closed at the lower by a piece of cover- 

 glass. Into t his cylinder is screwed the body-tube of the microscope 

 with eye-piece and objective, which are thus protected from the 

 water of the aquarium. The microscope is focussed by rack and 

 pinion (milled head just below the eye-piece), and in addition the 

 objective is screwed to a draw-tube, so that its position in the cylinder 

 may le approximately regulated. 



The arm of the socket is hinged to allow of the microscope being 



, faffs- ^. =r--^gt(, -=- "a? -~- 



<i*Fr r^ .--.T/ f .^.r,-v,'7r;?.-:- \'-r 



FIG. 210 



inelined ina plane parallel to the sides of t he aquarium. The loAVer 

 milled liead clamps the hinge at any desired inclination. 



'I 'I ie sockel also rotates on the arm, so thai tlie microscope can be 

 inclined in a plane parallel to the front of the aquarium. Thus any 

 point of t he aquarium can be readied. 



As an adjunct, and admirable aid to the student of t he lank and 



pond, as \\ell as a simple and easy means by which specific forms of 



microscopic life may lie found and readily taken, ue call attention 



the lank microscope of Mr. <'. Kolisselet. It is illustrated in fig. 



- 1 1 and scarcely needs Further description. 



< >ne of Zeiss's Steinheil aplaiiatic lenses, to which we ha\e 



