NOSE-PIECES 



291 



means of a lower : or to use the lower for the purpose of jiadiny a 

 minute object (such as a particular diatom in the midst of a slideful) 

 which we wish to submit to higher amplification. This was con- 

 veniently effected by the nose-piece of Mr. C. Brooke. \vhich, being- 

 screwed into the object end of the body of the microscope, carries 

 two objectives, either of which may be brought into position bv 

 turning the arm on a pivot. This is shown in fig. 230. 



The most generally useful of 

 all nose-pieces now in use arc 

 the rotating forms, which enable 

 one to carry two, three, or four 

 objectives on the microscope at 

 one time, and bv mere rotation 

 each is successively brought 

 central to the optic axis, seen in 

 figs. 231, 232, 233. as supplied 

 by Messrs. Beck. It is almost 

 unnecessary now to point out the 

 disadvantage of those older and 

 straight forms which involved 

 the danger of knocking out the 

 front lens of the objectives by 

 bringing it into contact with some part of the stage while the 

 other objective was being focussed. This objection was entirely 

 removed by the introduction of the bent form by Messrs. Powell and 

 Lealand, and adopted in the forms shown in figs. 231-233. There can 



FIG. 230. Brooke's nose- 

 piece, as made by Swift. 



FIG. -J.".l. 



FIG. 23-2. 



I'.y.'i. 



be no doubt that for ordinary dry lens work M>me such device is im- 

 perative. .Some, however, who do a very large amount of microscopical 

 work prefer to use two microscopes ; the one a third- or fourth-class 

 microscope, with only a coarse adjustment and a 1 -inch objective and 

 mirror, the other having a coarse and fine adjustment and a [-inch 

 objective, with a simple form of condenser and plane mirror, all fine 

 and higher-power work being left for a special microscope. 



The one drawback to the use of a rotating nose-piece is the extra 

 weight it throws upon the fine adjustment. As this subject is fully 



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