ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



295 



Fig. 43. 



defect may be remedied by making the sides of the nose-piece which hold 

 the objectives of unequal lengths, or by putting an adapter in either side 

 and so correcting for the difference of adjustment for focus. When 

 this correction has been made the convenience 

 of the nose-piece is much increased ; but the 

 error of want of concentricity may still remain, 

 i. e. a particular point in the middle part of the 

 field of the lower power may not also be in the 

 centre of the field of the higher. The appliance 

 now described has been designed to remedy the 

 defects both of want of centre and error of focus. 

 It consists of an outer brass collar, which in its 

 upper part is provided with a screw which fits 

 one of the screwed ends of the nose-piece, and 

 in its lower part consists of a brass collar, which 

 is provided with three mill-headed steel screws, 

 placed at regular intervals in its circumference. 

 These screws control an inner ring, into which 



the objective is screwed, and which may be moved laterally by means of the 

 steel screws. This inner ring, and also the outer ring which supports it, 

 may be made of any suitable length, and by this means the accurate adjust- 

 ment for focus is effected ; while the inner ring being, as already men- 

 tioned, capable of a lateral movement, the adjustment for 'centre' may 

 also be accurately made." 



TurnbuU's Improved Sliding Nose-piece and Adapter.* — The Eoyal 

 Scottish Society of Arts has awarded a silver medal to Mr. J. M. TurnbuU 

 for this apparatus, which he thus describes : — 



" It consists essentially of a small face-plate or ' chuck,' which screws 

 into the ordinary ' nose ' of the Microscope, fig. 44. On its face this has a 

 slide, which has fitted into it another sliding-piece, and 

 into which the objective is screwed. As many of the 

 other objectives as belong to the instrument are fitted 

 with similar sliding-pieces, which also fit into the first. 

 Once, therefore, an objective is fitted and centered 

 with one of these sliding-pieces, having a sufficient 

 length of tube to bring it very nearly into focus, it can 

 be substituted in a moment for one of lower or higher 

 power, as the case may be ; and if an object has been 

 previously centered on the stage with a low power, it 

 will be found accurately centered in the field of that 

 of the higher, I also wish to draw your attention to the fact that all the 

 face parts of this appliance are finished on the lathe, which enables the 

 optical axis of the eye-piece, instrument, and objective to be truly main- 

 tained, and does away with the failings of the ordinary double nose-piece 

 in this respect. Another form of this adapter is to have two, three, or 

 more objectives mounted together on one of the sliding-pieces, having on 

 each objective a sufficient length of tube to bring it accurately into focus, 

 and sliding one objective on another, as may be wished, central with the 

 tube of the instrument, a small spring-point retaining it in that position. It 

 is a matter of choice, however, as to which is the better form — whether it 

 will be more convenient to have two or three objectives mounted together, 

 or to have them separate. 



Having thus described the appliance, I think I may fairly claim for it 

 that it will change the objective of a Microscope with great rapidity, with 

 * Trans. Edinburgh Naturalists' Field Club, i. (1885-6) pp. 335-6. 



Fig. 44. 



