The Mickoscope. 101 



Fasoldt's spring nose-piece for the ordinary society- screw to carry 

 the objective, and an adjustment for withdrawing at will the cover- 

 glass reflector from the optical axis, consists of an ingenious arrange- 

 ment of shutters at the side, by means of which light is admitted 

 only through a long, narrow slit that is adjustable in both width and 

 position. With this arrangement a variety of bright or dark field 

 effects were obtained by slight changes in the position of the lamp 

 and the adjustment of the slit. When the image of the illuminating 

 flame was formed by the objective just at the edge of the field of 

 view and slightly out of the plane of the object, a transparent effect 

 was produced over a considerable portion of the field, presumably 

 by internal reflection at the bottom of the dry-mounted cover-glass, 

 on the lower surface of which the lines were ruled, and in the bright 

 portion of the field the lines of the lower-middle bands were very 

 easily and distinctly seen. 



Starting from any of the coarser bands, where there could be 

 no question about the lines, the plate was moved across the field by 

 means of the steady mechanical stage, and the lines of successive 

 bands appeared with distinctness but increasing fineness up to the 

 band claiming 110,000 to the] inch, which was seen with perfect 

 ease, and the alleged 120,000, which was seen clearly and repeatedly, 

 though with difficulty, while in^higher bands no trace or suspicion 

 of lines was perceived. The same limit was I'eached in several 

 separate trials by the writer, whose eyes, however, by'reason of long 

 over-use, should set no limit against the reasonable claims of others 

 presuming to go further. Mr. Fasoldt himself did not seem to 

 recognize the lines nearly as far up in the series as this ; but his 

 son, Ernest C, who was depended upon for most of the manipula- 

 tion, was positive that he saw the lines in the "130,000" band, and 

 none beyond that. Any importance attached to his judgment at this 

 interesting point must be viewed in connection with the fact that on 

 another occasion he was satisfied that he resolved a ''200,000" band. 

 No attempt to measure the spacing of the lines was made at that 

 time, and none is ready to report now. 



Mr. Fasoldt's faith in the integrity and visibility of the still 

 higher bands, which faith, it is scarcely necessary to say, is not 

 known to be shared by any scientific man, seems to depend wholly 

 on his belief in the infallibility of his carefully concealed method of 

 ruling them, and upon his impression that he has seen the lines as 

 high as " 150,000," and upon the equally firm impression of a few 

 other persons that they have seen all up to and including the 



