OF THE MICKOSCOPE. 47 



necessary. One of the most common models is that shown in Fig. 

 12. This form, although modern when compared with the micro- 

 scopes of Adams, Baker, etc.. is one of the oldest in use. It 

 was, \ve believe, devised by Wollaston, as a stand for his 

 doublet, and was afterwards modified by Fraunhofer, whose 

 microscopes on this model were almost identical with that 

 shown in the engraving. It is now too well known to need 

 elaborate description, and the smaller sizes are still sold ex- 

 tensively for the use of young people. Being manufactured in 

 large quantities, they are sold very cheaply, when the quality 

 of the lenses is taken into consideration. Therefore, until 

 some manufacturer concentrates his efforts upon the produc- 

 tion of the more convenient forms, and 

 turns them out in very large numbers, 

 the vertical microscope will probably 

 maintain its place in the market, and 

 many beginners will be led into buying 

 an instrument which, even in its most 

 complete and perfect form, will almost 

 certainly be a source of dissatisfaction. 



Aside from any deficiencies which may 

 exist in the optical parts of the instru- 

 ment, the objections to this model are the 

 small size and inconvenient form of the 

 stage ; the fact that the microscope can be 

 Used only in the vertical position, which, 

 although occasionally very useful, is the 

 worst position in which the instrument 

 can be placed for protracted observations, 

 and the arrangement of the mirror, which 

 renders the proper management of the illu- 

 mination impossible. Therefore, when- 

 ever there is a possibility of choice, some 

 form other than the vertical should be 

 chosen. 



Occasionally microscopes of this kind 

 Fig. 12. are furnished with achromatic objectives of 



VERTICAL MICROSCOPE. p re tty fair quality. In such cases the ob- 

 jectives and eye-pieces, if they could be 



