1899] MIC1108C0PICAL JOURNAL. 85 



Nobert's Bands. Micrometer Rulings. 



F. L. JAMES. M. D. 



ST. LOITIS, MO. 



Bands of rulings on glass, were first made by M. No- 

 bert, a Frenchman, some forty or fifty years ago. Prior 

 to the preparation of these rulings, and indeed, down to 

 a comparatively recent period the only method of testing 

 the amplifying and especially the defining powers of mi- 

 croscope objectives, was trying them on certain well-known 

 test-objects — the scales on certain butterfly or moth- 

 wings, certain frustules of diatoms, etc. M. Nobert de- 

 vised an instrument for ruling on glass, with a spicule or 

 splinter of diamond; lines at a definite and known dis- 

 tance from each other. These lines were arranged in bands, 

 commencing with a comparatively low number to the mil- 

 limeter, and gradually increasing, each band containing 

 ten lines and consequently decreasing in width as the 

 lines were placed more closely together. At first M. 

 Nobert made the bands of known dimensions, 100, 200 

 etc. up to 500 or 1,000 or 10,000 to the millimeter, but 

 later on he made the bands consist of lines whose spaces 

 were an unknown quantity, thus making each possessor 

 of one of his rulings determine the value of each band 

 for himself. This was done on account of the very im- 

 portant part played by imagination or rather by the 

 knowledge of the number, a knowledge which would 

 cause the observer, knowing the real number, to imagine 

 that he saw and was able to count the lines. The follow- 

 ing is a summary of the Nobert plates as known to the 

 writer, and he is of the opinion that it embraces all of 

 that artist's work, though there may be other series : 

 Ten band plates, running from 11,259 to the inch, up to 

 50,667, with no regularity between tha series — thus No. 

 1 being 11,259, No. 2, 13,100; No. 3, 15,300, etc; thirteen 

 band plates, runnlngfrom 45,000 up to 112,595 to the inch ; 



