The Microscope. 1^7 



P. C. C, M. D., New York. — In order that your question in regard 

 to the society screw might receive the most careful attention, we 

 have asked Mr. Bausch, who was appointed on the committee of the 

 A. S. M. to consider this matter, to give us whatever information he 

 could. Below we print his letter in full. 

 Editors of the Microscope : 



Your favor of the 20th inst. is at hand, and it gives me pleasure 

 to impart as much information on the subject of society screw 

 as possible. 



When I read a paper on the subject in '84 I looked up all the 

 literature on the subject which I could reach. I also had a copy 

 of the report of the original committee which determined the stan- 

 dard screw, and quote below their words : 



" A screw, containing 36 threads to the inch, having an angular 

 thread of 54 degrees, slightly rounded off at the top and bottom, 

 has been considered the most appropriate. The largest linear 

 aperture, at the junction of the object-glass with the body of the 

 microscope, will be required for objectives of low power having the 

 widest compatible angle of aperture ; this is not likely to exceed .72 

 to .73 inch with the greatest diameter of field-glasses now in use ; 

 hence .8 inch may be taken as sufficient for the external diameter of 

 the screw. The length of screw recommended is ^ or .125 inch 

 comprising four and one-half threads, and that of the guide or 

 collar .15 inch." 



You will note the ambiguity of the instructions. Prof. Rogers 

 and myself, as committee of the American Society, have endeavored 

 to induce the Royal Microscopical Society to take the matter in hand 

 and at least co-operate with us, but all the definite information 

 which we have been able to receive has been to the effect that they 

 consider a change impracticable on account of the expense involved 

 to the maker. 



We have not yet ceased to hope that something definite may be 

 effected, but have not been able to do more on account of the want 

 of time. You, as well as almost all microscopists, are aware of the 

 discrepancies in the standard screws, and your journal would no 

 doubt be doing a good service by favoring a proposition to do some- 

 thing to change this state of affairs. The American manufacturers 

 have all expressed themselves in favor of adopting a standard on 

 which dependence can be placed. 



With kind regards, I am, 



Very truly yours, 



EDW. BAUSCH. 



