60 



being the expense involved, so that we must con- 

 trive to suffer until some concerted action is taken 

 by the manufacturers themselves, which we trust 

 will not be too far distant. 



Double Nose-Piece. In changing one objec- 

 tive for another to obtain another power, time is 

 consumed and it is often inconvenient ; besides, 

 there is danger of dropping the objective or dis- 

 turbing or destroying the object. To avoid this 

 the double (Fig. 24) the triple and quadruple nose- 

 pieces are offered, to the first of which two, to the 



next three and to the quadruple four objectives 

 may be attached in such a manner that, when fixed 

 to the nose-piece of the tube, each objective may 

 be in turn brought into use by swinging the nose- 

 piece and in such a manner that each is centered 

 and will be in focus, if not exactly, at any rate very 

 closely. Of all the conveniences in accessories 

 these are the most useful and in most common 

 use, the writer knowing from his experience as 



