232 WOODWARD, ON NOBERt's TEST-PLATE. 



error, as he will doubtless acknowledge when he examines 

 the photographs of the 12th, 13th, 14th, and 15th bands now 

 prepared, and copies of Avhich I have sent him. 



It only remains to indicate how the Nobert's lines may be 

 counted, even in the highest bands, without photographing 

 them. To do this, we set up the microscope as though to 

 take a photograph, remove the eyepiece, receive the image on 

 a piece of plate-glass, and ^dcAV it A\ith a focussing glass, on 

 the field-lens of which a black point is remarked. As the 

 focussing glass is moved on the plate from side to side, the 

 black point is moved from line to line. The lines may thus 

 be counted Avitli as much ease and precision as though they 

 were large enough to be touched by the finger. 



Or they may be counted by a cobweb micrometer, if the 

 precaution is taken to keej) the micrometer eyepiece separate 

 from the microscope, clamping it firmly about half an inch 

 from the end of the body of the instrument on a stand, which 

 should be screwed down to the table A piece of black 

 velvet should be used to connect the micrometer with the 

 microscope tube. It Avill now be found that turning the 

 micrometer screw communicates no tremor to the instrument, 

 and the lines can be counted with great ease. On the whole, 

 I think the first of these two methods preferable. 



A set of the photographs above described is herewith for- 

 warded to the editors of this Journal. 



Note. — Since writing the above, I have seen Mr. Stodder's 

 paper reproduced in the July number of this Journal, with 

 a note, in Avhich he claims that Dr. Barnard had resolved 

 the 19th band with a Spencer -yVth and a Tolles' J-th. 

 Dr. Barnard certainly saw lines in the 19tli band, as 

 Mr. Stodder and I have done, but undoubtedly these lines 

 were spurious, since the counts given in Mr. Stodder's note 

 do not agree with each other or ^^dth the true number of 

 lines; and Dr. Barnard himself writes me, July 21st, 1868, 

 that his opinions on the subject are not matured, and that he 

 intends to make further observations. 



