228 WOODWARD, ON NOBERT's TEST-PLATE. 



article from a letter recently received by him from Eulen- 

 stein, of Stutgard, in which that microscopist says, " I have 

 myself resolved the 14th band with a Virth of Powell and 

 Lealand." " Nobert himself has never seen with his highest 

 powers higher than the 14th band." Eulenstein would 

 hardly have written thus in 1868 if Schultze had resolved 

 the 15th band in 1865. 



After commenting on the various observations hitherto 

 published with regard to the Nobert lines, Mr. Stodder goes 

 on to state — " With Tolles' ^th immersion, angular aperture 

 170°, B eyepiece, power 550, Mr. Greenhaf and myself both 

 saw the 19th band satisfactorily." These gentlemen, how- 

 ever, were not able to count the lines, and Mr. Stodder en- 

 larges on the difficulty of counting such fine lines by any 

 means in our possession. He says, ''In counting lines of 

 such exquisite fineness either the microscope or the stage 

 must be moved, and it is next to impossible to construct 

 apparatus that can be moved at once the ttj oW-u^l^ ^2ixt of 

 an inch and no more." 



Shortly before reading Mr. Stodder's paper, I had com- 

 menced a series of observations on Nobert's nineteen-band 

 plate. These observations have convinced me that Messrs. 

 Stodder and Greenhaf saw spurious and not real lines, and 

 as the difficulty of counting the lines is readily overcome by 

 following the method I shall presently detail, I hope these 

 gentlemen will repeat their observations, and endeavour to 

 count the lines they see in the 19th band — an attempt which 

 I am sure will convince them that my opinion is correct. 



The following is a brief account of my own analysis of the 

 nineteen-band plate of Nobert. The plate used is the pro- 

 perty of the E.ev. Dr. F. A. P. Barnard, President of Colum- 

 bia College, New York. As in all the Nobert plates which 

 I have seen, the lines are ruled on the under surface of a thin 

 glass cover, which is cemented at the edges Avith Canada 

 balsam to a glass slide, on which the fractions of a Paris 

 line corresponding to the principal lines are written with a 

 diamond. 



This plate was obtained of Nobert in 1867, and by special 

 request the ruling had been made on a cover much thinner 

 than I have ever seen on other plates of Nobert. On trial 

 I found that I could readily employ the -ir-^ih. of Powell and 

 Lealand, and even with some difficulty the -j^th of the same 

 makers. 



Out of the series of lenses at my disposal, including a -|-th 

 of Ross made two years ago, a yV^h of Tolles made five years 

 ago, an immersion system No. 11, by Hartnack, made two 



