548 



PROCEEDINGS OF THE SOCIETY. 



Mr. Crouch said that he liad always used them as gauges, and not 

 as working screw tools. 



Mr. Crisp said that he could not pretend to discuss with Mr. Beck 

 the practical question ; all he could do was to point out that the gauge 

 and screw tools wLich wore now being issued by the Society were 

 identical with those which the Sub-committee appointed in 1857 

 ultimately decided should be issued. This was shown by comparison 

 with an original set belonging to Mr. Gay, which was produced to the 

 Meeting.* 



* The rensons which induced the Committee to substitute a tap and pair 

 screw tools for the cylindrical gauges and hob recommended in their first report 

 of 12th November, 1857 (see Trans. Micr. Soc. Lond., vi. (18.58) pp. 39-41) 

 were thus stated by Mr. Charles Brooke, F.R.S., Past-President of the Society 

 (see Trans. Micr. Soc. Lond., vii. (1859) pp. 92-7). The remarks are appended to 

 a paper of the late Mr. Richard Beck : — 



" It is unquestionable that an exact counterpart of the hob may be ma le by a 

 screw-cutting lathe ; but, for so fine a tliread, screw-tools may probably be equally 

 well hand-made by a practised workman. As very few opticians either possess 

 traversing lathes, or have had much experience in making screw-tools, it was 

 thought more desirable to have some screw-tools made from Wliitworth's hob by 

 an experienced workman, and supply them at cost price to the manufacturers. 



" The practical difficulties that (jccuried in the use of the cylindrical giiuges 

 may be thus explained. It is manifest that if the inside and outside screws wire 

 exactly the same size, that is, had exactly tl:e same longitutiinal section, they 

 \\ould fit each other as tightly as the cylindrical gauges, and would therefore t)e 

 useless for the purpose proposed. One of three courses must therefore be adopted 

 — either 



" 1. The outside screw being made to the exact gauge size, the inside screw 

 must be made a little larger, — or 



" 2. The inside screw being made to the exact size, the outside screw must be 

 made a li;tle smaller, — or 



" 3. Both inside and outside screws must be made to vary a little from the 

 exact size. 



•■ It soon occurred in practice, that object-glasses by one maker, who adopted 

 the first course, would not enter the body of a Microscope by another maker, who 

 adopted the second course ; and thus the proposed universality of the screw was 

 60 far set at naught. 



" As both the top and bottom of the outside screw can be most easily gauged, 

 it appeared to tiie committee more desirable to adopt the first course, by giving a 

 little ease to the inside screw ; and in order to ensure uniformity, to have a 

 number of steel taps or gauges made of such a size, that if the body of the 

 Microscope were made to receive one of them tightly, an object-glass having an 

 outside screw of the exact proposed dimensions would enter it e.isily and 

 pleasantly. These taps must necessarily, for the reasons previously stated, be 

 some two or three thousandths of an inch larger than the gauge size. 



"It does not appear that the cutting points of the ingeniou.sly contrived 

 adjustable screw-cutting gaugt s proposed by the autlior of the paper pos.sess any 

 immunity from the same wear as that to which, as he justly remarks, the screw- 

 tool is liable : nor would the mechanical effect of setting out the cutting points 

 differ from that of taking a slightly deeper cut with the screw-tool. 



" The form of the inside fitting represented in the drawing that accompanies 

 the paper, namely, with a plain pait beyond the screw, was that originally 

 recommended ; but as the committee were informed by the author of the paper, 

 as well as by another leading firm, that it would be more convenient in practice 

 to continue the inside screw to the lull extent that the objt ct-glass enters, and 

 that it was their intention to do so, the committee thought that it would be better 

 that their recommendation should in this respect be rendered conformable to the 

 existing practice. It was also considered that this course would supersede the 



