POWELL SWIFT 85 



The mechanical stage, which rotates concentrically, and is 

 provided with centering screws for adjusting it to the optic axis, is 

 a modification of that of our " Premier " model. The substage 

 introduces an entirely new feature. It is provided with two cradles 

 on the principle of the Sloan Objective Changer, introduced by 

 Messrs. Beck, so that the whole of the substage apparatus, when 

 mounted in interchangeable fittings with centering adjustments, can 

 be instantly inserted in the substage, two pieces of apparatus being 

 capable of insertion at one time. The body of the microscope is 

 provided with a similar cradle, so that nose-pieces of a special 

 character can instantly be interchanged if desired. For instance, 

 the plain nose-piece may be replaced for petrological work with a 

 nose-piece containing an analysing prism, Bertrand lens, quartz 

 plate, etc., or with a nose-piece containing a high power vertical 

 illuminator or other apparatus. The advantage of this system is 

 applicable also to a great deal of physics research, as by introducing 

 special apparatus into the substage or nose-piece, as occasion may 

 require, a most perfect optical bench can be produced for general 

 experimental work. There is a considerable class of delicate optical 

 research which calls for an optical bench possessing the perfect 

 adjustments of a microscope, and we believe that hitherto this 

 requirement has not been met. By examination of the instrument 

 it will be seen that almost any class of apparatus could be applied 

 to the stand for making small and accurate measurements in physics, 

 and although the chief object of this instrument is to provide the 

 most perfect microscope that can be required, the other function 

 for such an instrument has been borne in mind. 



The base of the microscope is of the English tripod pattern, but 

 has been provided with a new feature which is specially useful for 

 photomicrography and optical bench work, which will also be appre- 

 ciated by the ordinary observer. A hook shape casting is supplied 

 which can be screwed down to the bench or camera, and an eccentric 

 bar passing through the centre of the base w^ill slide underneath 

 this hook, when, by a slight motion of a lever at the side, the base 

 of the microscope is locked firmly down in an exact position. Another 

 lever between the uprights of the base clamps the joint by means 

 of a right and left hand screw. 



We have not alluded to the rack and pinion adjustments of the 

 hody, the stage, and the substage, which are of the usual spiral 

 type, but might well call attention to the great width of the slides 

 employed to give great stability to these adjustments. 



It was decided in the consultations which took place towards the 

 production of this microscope that while Messrs. Beck were employed 

 on their standard instrument, we should undertake the manufacture 

 of this special type, which would in all probability be sold by both 

 the firms by whi^h i't is manufactured. 



