PART II. 



THE MECHANICAL AEEANGEMENT OF THE 

 MICBOSCOPE. 



WE have thought it desirable to devote a special chapter to the 

 mechanical arrangement of the Microscope, for the sake of those 

 readers who have not the opportunity of referring to other 

 micrographic works. We have limited ourselves, however, to a 

 short explanation of the principles followed in the different 

 manufactories of the better-known opticians. 



I. 



GENEEAL EULES FOE THE CONSTEUCTION OF 



STANDS. 



TJie Focusing. The stand of the compound Microscope is, in the 

 first place, intended to bring the objective to the proper distance 

 from the object, and to retain it firmly in this position. For this 

 purpose it must be so constructed as to admit of considerable altera- 

 tions of distance between the objective and the stage (for instance, 

 when changing the objective), and also be provided with means for 

 delicate adjustment to a given level. The mechanism for these 

 purposes allows of three modifications, each of which is used in a 

 very different way. The focusing takes place (a) by movement of 

 the body -tube towards the fixed object-stage, upon which the object 

 under investigation is placed, (b) by movement of the stage towards 

 the fixed body-tube, or (c) by a combination of both movements, 

 where that of the body- tube serves for the coarse adjustment and 

 that of the stage for the fine adjustment. Each of these arrange- 



