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less importance, as it would be found that they might shift the eye-piece 

 laterally without making much apparent difference. 



Dr. Matthews said that in connection with the question of the simplest 

 mode of attachment it occurred to him that there was an instrument in 

 common use, a stomach pump, in which the joints fitted together as cones, 

 and so perfect did this method seem that he never knew a case in which a 

 joint had given way. If the objective and nose-piece were fitted together 

 in this manner by a cone of sufficiently small angle, he could conceive of 

 nothing more simple which could be adapted to the purpose. 



Mr. Hailes said there seemed to be considerable analogy between the 

 fitting of an objective and the chucks of a lathe. It was well known 

 that if work was removed from a lathe fitted with an ordinary screw chuck 

 it was almost impossible to bring it up to truth again by screwing up. 

 With respect however to the cone fitting, he was speaking about it a short 

 time ago to the proprietor of a large engineering wprks, and that gentle- 

 man told him he considered it the best fitting for lathes that could possibly be 

 used, and he had done away entirely with screwed nose-pieces in favour of 

 the cone. As to its power of holding, he, Mr Hailes, might say that he saw 

 a lin. iron bolt screwed perfectly at one cut with dies held in a chuck so 

 fitted, and he was told that with this kind of fitting the chuck could be 

 taken off and replaced with perfect accuracy. 



Dr. Matthews said he had often seen this difficulty of getting the same 

 degree of truth when replacing work in the lathe with the shoulder 

 screw, and had noticed that a workman would use a piece of brown paper 

 packing in order to get exactly the same adjustment as before. 



Mr. Nelson said that he believed the reason why Powell and Lealand's 

 lenses fitted into their bodies so absolutely true was that they made all of 

 them to screw up to exactly the same point of the screw. But when an 

 objective of another optician's make was put upon one of their bodies, 

 though it was the same thread, it would not screw up with the same degree 

 of accuracy. All depended upon the point at which the screw came up to 

 the shoulder. With regard to the cone, he believed it to be the best fitting 

 in the world, and for his own part he should be glad to see the whole 

 system of screws swept away and the cone substituted. 



Mr. T. Curties exhibited and explained the action of Pease's " Facility " 

 adapter, in which three gripping jaws are caused to advance and recede 

 on turning a loose collar, somewhat in the fashion of the well-known 

 American "grip" chuck for lathes. A grooved ring is screwed upon the 

 object glass, which only then requires to be inserted into the adapter, when 

 a partial turn of the loose collar accurately centres and secures it in its 

 place. Mr. Curties also exhibited a modification of this, which he had had 

 made. In this modification the gripping jaws were made somewhat wider, 

 and were threaded on the inside, so that they might grip the screw thread 

 on the objective, thereby doing away with the necessity for the grooved ring 

 of Pease's arrangement. He thought this form offered the very great 

 advantage of saving the time and trouble of screwing and unscrewing in 

 about as simple and complete a manner as could be devised. 



