" The Examination of Nohert's Nineteenth Band." 121 



If the rulings and the counts are both correct, one division of 

 the first band should be equal to ten of the nineteenth ; one of the 

 second to 6| of the nineteenth ; one of the third to five of the 

 nineteenth ; and one of the fourth to four of the nineteenth. 



I. ^ = 193-50. And ^^- xlO = 195- 50. 



6 20 



n. ii^ = 128-78. And ~ X 6|= 130-33. 



III. m^ = 96-50. And ^ X 5 = 97-75. 



IV. i?3- = 76-86. And ^ X 4 = 78-20. 



The coincidences are not exact; but they are too close to be 

 accounted for on the supposition that the lines in the nineteenth 

 band are spurious. 



The following are specimens of measurements made at the same 

 time to determine the value of a French line in divisions of the filar 

 micrometer, by measuring the divisions of a stage micrometer, in 

 which the British inch is divided into 1000 parts; a covering glass 

 having first been placed over the stage micrometer, as nearly as 

 possible equal in thickness to the Nobert plate. Both lines of the 

 filar micrometer were employed in this measurement, having been 

 first adjusted so as to throw the total index error upon one. Each 

 thread was then moved over one one-thousandth of an inch, with 

 the following results : — 



Index error, left screw = 0, right screw = + 42. 



I. Left Screw. Eight Screw. 



»" = 2162div. -A_" = 2211 -42 = 2169 div. 



-i- " = 2162 + 2169 = 4321 div. 

 1000 



1 inch = 2,160,500 div. 1 line (British) = 180,041 -7 div. 



81 

 180,041-7 X — = 190,676 div. = 1 line French 

 76 



Another portion of the stage micrometer being brought into the 

 field, a second measurement was taken, thus : — 



II. Left Screw. Eight Screw. 



_L^" = 2167 div. ^" = 2248 -42 = 2206 div. 



-^" = 2167 + 2206 = 4373 div. 

 1000 



1 inch = 2,186,500 div. 1 line (British) = 182,208-3 div. 



K 2 



81 

 182,208-3 X ^ = 193,011 div. = 1 line French. 

 ' 76 ' 



