124 



MECHANICAL ARRANGEMENT OF THE MICROSCOPE. 



The following are the authors' remarks on the general part of 

 the subject : ] 



It may not, however, be superfluous, as a supplement to what 

 has been said, if we point out the importance of several points 

 omitted in the introduction, which, according to our experience, 

 deserve special consideration in a critical examination of stands. 

 We place in the first rank of importance accurate and durable 

 metal-work. It is by no means a matter of indifference whether 

 the thread of the screws, the focusing arrangements, &c., are of 

 durable construction. On this point we have been able to convince 

 ourselves in the workshop of C. Zeiss, of Jena, how much more 

 exactly the parts of the stand (as, for instance, the pillars and the 

 socket, slides, &c.) may be made and fitted together if the metal is 

 worked by the Fraising machine, instead of being turned or planed. 

 Of the special features which a good stand 

 should possess, the chief are : (1) The 

 solidity of the mechanism of the focal ad- 

 justment, which always leaves much to be 

 desired. The shifting of the image, the " back 

 lash" of the screw, &c., are well-known 

 disadvantages almost invariably present in 

 the older stands. On this point also we have 

 met with some important improvements in 

 the workshop of Zeiss ; but we must not 

 expect the friction due to the existing modes 

 of construction can be completely eliminated 

 by slight alterations in the construction of 

 the instrument. Whether the fine adjust- 

 ment devised by Seibert and Krafft will 

 be really durable, time must show. As far, 

 however, as the principle of construction 

 exhibited in Fig. 79 admits of a judgment 

 on the point, friction is reduced nearly to 

 a minimum. The micrometer-screw s acts 

 upon the funnel-shaped head of the rod m, 

 the upper end of which acts in a similar 

 manner upon //, the solid bar attached to 

 the socket of the body-tube. The ring r, 

 which serves as a guide-piece, lies loose in the hollow column, 

 and as a rule does not touch the rod ; its function is merely 

 to prevent the point of the rod from slipping out of the notch 



