ROYAL MICROSCOPICAL SOCIETY'S SCREW. 19 



in two rectangular directions, so that the remarks made 

 in Dr. Carpenter's 'Microscope' do not now apply 

 to it. 



Crouch's "Premier Binocular" is also one of the first- 

 class instruments. An illustration of it is given in 

 Fig. 10. 



Messrs. Pillischer, Browning, Murray and Heath, Baker, 

 Watson, and others make medium priced stands of con- 

 siderable excellence, but seeing that all the principles of 

 construction are exhibited in the foregoing, it would be 

 mere repetition to give illustrations of each. 



After all, a microscope stand must satisfy certain con- 

 ditions, and if these be fulfilled it scarcely matters to the 

 owner who the maker has been. It must be made of 

 good hard brass, be furnished with a heavy foot, and well 

 balanced, so that it may be placed in any position without 

 overturning. All the rackwork and screws must move 

 easily, firmly but not stiffly, and without " loss of time " or 

 " backlash." Stops should be placed so that the body may 

 be set either horizontally or vertically as required, and 

 plane and concave mirrors should be always provided, 

 preferably on a jointed arm. The lower extremity of 

 the body should be furnished with the Society's screw, 

 and no microscope should be purchased which has not this 

 thread. 



A mechanical stage is not absolutely necessary but is a 

 great convenience, despite all opinions to the contrary, and 

 some accessories cannot be used without it. A circular and 

 rectangular motion should be capable of being imparted to 

 the stage without the intervention of rackwork ; but a 

 duplicate motion by means of rack and pinion should be 

 supplied to the better instruments. Reasons for the rota- 

 tion of the stage will be found in the chapter treating on 

 the use of the polariscope. 



C 2 



