Grayson s New Ten-Band Plate. By A. A. C. Eliot Merlin. 163 



¥7 7T8> or 0*00002090 in., the true mean diameter of the lines with 

 the proper antipoint correction applied thus being 0- 00002488 in. 



In order to ascertain the results obtainable on certain of the 

 rulings with much lower apertures and magnifications, the following 

 measurements of the first, second, and tenth bands which are shown 

 in the last three sets of columns of the table were effected. With 

 these lower powers the images of the lines themselves did not prove 

 nearly so satisfactory as with the preceding optical arrangements, 

 although all the lenses utilized are picked specimens of their class. 

 The difficulty of accurately setting the wires on the lines was much 

 augmented, and it proved impracticable to secure double readings. 

 To make matters worse, a small setting error now represents a far 

 greater real distance than is the case with the high magnifications. 

 It is true that the means are often close, but this is mainly due to 

 the plus and minus errors compensating each other. 



The outcome of my experience with the foregoing fairly ex- 

 haustive measurements is to convince me, beyond the shadow of a 

 doubt, that the lower magnifications are wholly inadequate to reveal 

 the minute real variations in lines and spacings of the new plate, 

 while I feel equally certain that the higher magnifications employed 

 are quite capable of doing so when used with proper appliances and 

 strictly critical conditions, for it is especially necessary that the 

 lines themselves be resolved so that their individual irregularities, 

 trifling as they are, may be rendered clearly recognizable. If any- 

 one who has not performed the arduous work under the specified 

 conditions should cavil at the excessively small real differences 

 indicated, and contend that such quantities are altogether beyond 

 the grasp of the Microscope, the only alternative is that the latest 

 production of Mr. Grayson possesses no real inequalities capable of 

 demonstration under the highest powers and most perfect instru- 

 mental means at our disposal. 



Addendum. — The essential measurements on which this paper 

 is based not being printed fully in their original form, although 

 they have been ably abridged and handled by a member of the 

 Society's Council, the author nevertheless finds it necessary to 

 request the indulgence of those familiar with refined practical 

 micrometry for any shortcomings or failure of the abridged 

 figures, given herewith, to properly sustain all the claims made in 

 the text, which, under the unavoidable circumstances, may, in 

 some instances, appear to be unsupported by adequate evidence, 

 or even resemble mere assumptions. This is practically inevitable 

 with any curtailment of the full figures and measurements of the 

 individual spacings, which are, in themselves, means of double- 

 edge readings. 



