300 SUMMARY OF CURRENT RESE ARCHES RELATING TO 



lines in tho band of 130,000, clear and well-defined, after tho instrument 

 was focused. Unaided ho was unablo to go beyond tbo 90,000 band. 

 This trial was in ado after a railroad trip of ten week-days and five nights. 

 Tho vision was not as acute, and the touch of tho fingers was not as 

 sensitive as usual. In about a week afterwards, at a second trial, ho 

 "saw all of the lines to tho 1C0,000 band, which ho was unablo to 

 resolve." Tho 170,000 and 180,000 bands ho " did not resolve, but tho 

 190,000 band came out sharp and clear. This was all ho could do at 

 that time. Tho delicacy of focusing is probably as difficult as tho dis- 

 cerning of tho lines." 



Photomicrograph No. 4 was of a quadruplo ruling, tho central bands 

 being 80,000 per inch. When both sets of lines are illuminated, tho 

 6pectra produced are gorgeous. " Mr. Fasoldt states that rulings which 

 do not produco spectra are not resolvable, and ho discards such rulings, 

 as tho lines aro ruined." 



" Theso rulings aro of very great interest to tho microscopist, as a 

 measure of what can bo done by different methods of illumination. 

 After many trials by transmitted light, the baud of 90,000 lines per 

 inch was tho most I could resolve. Mr. Fasoldt says tho 110,000 band 

 is the highest one he knows to have been resolved by the same 1/12 

 objective by transmitted light. It would bo very interesting to know 

 what kind of rulings Prof. Abbo used in determining the theoretical 

 resolving power of an objective, as well as the method of illumination." 



(2) Dr. Ward's Report on the Examination of a Fasoldt Test-plate. — 

 Dr. K. H. Ward's report was embodied in remarks mado at the Pittsburg 

 meeting of tho American Society of Microseopists. The following is 

 furnished to us by the author : — 



The plate consists of twenty-three bands ruled on a cover-glass, 

 beginning at 5000 lines to the inch, and increasing by 5000 each timo to 

 30,000, and thence by 10,000 each time to or toward 200,000. The lines 

 aro ruled alternately longer and shorter, so that tho 40,000 band becomes 

 at each end a 20,000 band with interlying lines, and the " 200,000 " band 

 should be seen, if resolved at all, as a 100,000 band similarly interlined. 

 The extraordinary mechanical skill of the maker and his success in 

 ruling the lower bands attach real interest to the plate, and to his 

 methods of studying it, in respect of the possibilities of fine ruling and 

 of extreme resolution ; an interest which is enhanced rather than dimi- 

 nished by tho maker's t asy faith in the character and visibility of tho 

 highest bands and his inability to apprehend the mechanical uncer- 

 tainties and scientific absurdities involved in this belief. If he has done 

 even a small portion of what ho thinks, ho has far surpassed all other 

 experimenters, as far as yet proved, and has earned and will receive the 

 credit that he claims. 



Upon learning of the appointment of a committee to consider 

 the subject, Mr. Fasoldt tendered a request that he might be allowed 

 to be present when the plate was examined, and kindly offered 

 the use of his apparatus, and also of his own services, "to show the 

 lines " to the Committee at any time. Believing it to be of scientific 

 as well as historic interest and importance to know exactly what he saw 

 and how he saw it, I replied that while it would be impracticable for 

 the Committee as a whole to make the proposed arrangement, as a 

 member of tho Committee I would gladly accept his offer to show the 

 lines, and that the lines desired to be seen were those of the higher 



