Anomalies in Objective Screw Threads. 177 



others a mean, and the remainder the maximum size or too large 

 altogether. 



Next, a few remarks mav be made with regard to the standard 

 sizing gauges which are supplied by the Society. The purpose for 

 which these are intended is not as gauges as ordinarily understood 

 in a workshop, but are so set that if an objective is arranged to 

 screw into the die, and the nose-piece of the Microscope is sized to 

 receive the tap, the objective will undoubtedly enter the nose-piece, 

 but it will have a considerable shake. 



The specification gives exactly the same limits and sizes for 

 these gauges as for the objectives and nose-pieces respectively 

 themselves, and this in itself is an element of weakness. There is 

 no reason why the tap and the die should not be made within far 

 closer limits, in fact of a specified size with a very small limit of 

 possible error. 



As a matter of fact, the set which I have tested is just the 

 mean between the maximum and the minimum. 



3. We have now to consider how uniform results could be 

 attained. In the first place I should suggest that the specification 

 were revised, and that the diameters of threads of object-glasses 

 and nose-pieces at the top and bottom of the threads were given 

 in absolute figures, these figures to be the maximum size of objective 

 thread and the minimum size of nose-piece thread permissible. Any 

 latitude that is to be taken advantage of should be a minus quan- 

 tity for the objective and a plus quantity for the nose-piece. 



Next, if it were thought well to adhere to the present sizing tap 

 and die, seeing that the die has adjustable jaws, a master male- 

 gauge should be supplied smaller by a small amount than the 

 specified size, and that difference should be indicated upon it. This 

 master gauge would be kept in the office in the works, and from 

 time to time the adjustable jaws on the die would be set to it, and 

 thus a standard would be maintained. 



Alternatively, or in addition, a pair of limit gauges could be 

 supplied by the Society to which all objectives and all nose-pieces 

 would be referable. Any maker having such limit gauges, exer- 

 cising care and wishing conscientiously to adhere to the standard 

 thread, the correct shape of screw thread being assumed, would not 

 then be able to send out an objective or a nose-piece that would not 

 receive other makers' fittings. 



These proposals are submitted by way of suggestion only, and 

 it is hoped that they may lead to consideration of ways and means 

 that may have a practical outcome. 



