292 



ACCESSORY APPARATUS 



t rented under the heading of ' Microscope,' no more will be said at 

 present than that a double nose-piece is to be preferred to a, triple, 

 and a quadruple need not. be entertained tor a delicate instrument 

 when made of ordinary metal, unless it is required to find out in how 

 short a time a fine adjustment may be ruined; for let it be noted 

 that a ~2 inch. 1-ineh. .\-inch, and ^-iiich objective of English make 

 weigh together 8', /. without any nose-piece. But Messrs. Watson 

 and Son have de\ ised and made in aluminium a dust-proof triple 

 no>e-piece, which, where it is required to be used, reduces the objec- 

 tion.-- to its employment to their minimum, and not only in greatly 

 reduced weight, bill in other ways, makes its use more feasible 

 without strain upon the fine adjustment or danger of injury to the 

 objectives. In many nose-pieces, if the objectives should be acci- 

 dentally left so that neither of them is in the optical axis of the 

 microscope, there is nothing to guard the back lenses of the objec- 

 tive.- from dust and moisture. Messrs. Watson devised a dust- 



- :; 1- ^ Bison's dust-proof aluminium nose-piece. 



PlG. _!;;:>. Section ,,f Mir alx.vc. 



proof arrangement, consisting of an upper and an under disc, having 

 a spherical curve; to the lower disc are fitted three small screw 

 tubes which receive the objectives. This plate rotates upon a centre 

 pin, and as each objective is brought into the optical axis of the 

 micrn.se,, pe its axial coincidence is indicated by a, spring catch. The 

 edge is Covered \\ith a metal rim. making it dust proof.' The weight 

 "f ( ']"' "rd i nary l.rass nose piece is 4 ; j o/.. ; the \\eight of this one is 

 Simdar instruments are made by other makers, but the 



lust proof arrange nt and the extreme lightness are. so far as we 



enow, characteristic of the instrument of .Messrs. Watson. We 

 illustrate this nose-piece complete in !i-. :2:U, and in an enlarged 



* t \ O 



< ( f I i / 1 1 i iii \ i * . ) ' ' . 



section in fig. -i:\:>. 



r the proper use of a rotating nose-piece the length of the 

 ive mounts should be so arranged that when the objective is 

 hanged little focal adjustment \villbe necessary. 



.''I! 'lit calotte nose piece for four objectives is made by 



