1885-86.] Edinburgh Naturalists' Field Club. 335 



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 de- 

 scribed 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 nosepiece ; 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 

 adjustment for focus is effected ; while the inner ring being, as 

 already mentioned, capable of a lateral movement, the adjustment 

 for " centre " may also be accurately made. 



At the same meeting, Mr J. M. Turnbull exhibited an improved 

 sliding nosepiece and adapter for the microscope. The following 

 explanation of these was made by the inventor : — 



ON AN IMPROVED SLIDING NOSEPIECE AND ADAPTER 

 FOR THE MICROSCOPE. 



In introducing this small piece of apparatus to your notice, it is 

 not my intention to enter into any elaborate description of what has 

 already been done in this direction. But you will perhaps allow 

 me shortly to notice one or two of the contrivances that are used 

 for this purpose — viz., changing the object-glasses of microscopes. 

 The best known and most largely used of these are the ordinary 

 double and triple nosepieces. These nosepieces are, no doubt, 

 a most useful invention, but they are not without their defects. 

 They are rather difficult and troublesome to make, and, unless 

 the work of a really first-class optician, are usually worthless. 

 Even in the best of them, the optical axis of the object-glass does 

 not coincide with that of the eyepiece and instrument. This is 

 an objection which is fatal to good work ; and no matter how 

 good the objective, if its axis is not in line with the eyepiece, it 

 goes a great way to detract from its usefulness. There are also 

 very few nosepieces which will stand the test of having an object 

 on the stage of the microscope centred under a low power, and, 

 having turned down the high power, to find the part wanted in the 

 middle of the field. It is more than likely that it will be some- 

 where on its edge, or not in the field at all. Notwithstanding 

 these defects, the nosepiece is without doubt the best appliance 

 at present in use for the purpose — the other inventions, such 



