ox A TABLE OP STANDARD WAVE LENGTHS OF THE SPEClliAL LINES. 107 
Grating. D. Correction. Final Values. 
I. 5896.20 -.02 5806.18 
II. 5896.14 +.09 5806.23 
III. 5896.28 -.06 5896.22 
IV. 5896.14 +.03 5896.17 
Mean value, 5896.20. 
This is very nearl}^ the value given by Dr. Bell. 
The determination of Mr. C. S. Peirce of tlie U. S. Coa.si Survey i-^ r(M-fnii»]y 
a very accurate one. Dr. Bell and myself have made some attempts to cmHIm-iIo 
his gratings, which he sent to us for the purpose, and to correct for the scnle u^ d 
by him. There is great uncertainty in this process, as we had only a portion of 
the necessary data. The correction of his scale was also uncertain, bccau-c tho 
ass scales used by him may have changed since he used them, in the iiinnmT 
thermometer bulbs are known to change. Correcting, then, only for the error ol 
ruling in the gratings, we have : 
Peirce's value 5896.27 
Correction * —-07 
5896.20 
The correction for the scale would be about as much more in the same direction, 
provided the glass scales had not changed. But it is too uncertain to be used, 
although I have applied it in my preliminary paper. 
Kurlbaum's result, made with two good modern gratings, has the d,.fect that 
the ffratincrs were 42 and 43 mm. broad, quantities which it is impossible to conipaiu 
with a meter. His small objectives, one inch in diameter, could mU 
j^....... 
ly 
from the whole L^rating, and so the grating space 
ned 
£)"— '"D 
fl 
the portion of the grating used. The spectrometer w.is poor, and the errors 
of the frratinor undetermined. 
Muller arid Kempf used four gmtings, evidently of vei-y poor quality, as they 
give results which differ 1 in 10,000. . 
The result of An.sfom was a marvel at tl,e time, but ll.e ^obert gratn . 
Takiiv Thalen's correction lor 
■o 
n 
used by him w^ould now be considered very pooi , . , . u.- n.v 
error of scale, we have for the mean of the E lines 5260.S0, -l-b P^cs, b, my 
table of relative wave lengths, 2> = 5895.81. It is rather disng 
the relative accuracy of observations made by different ob 
to cstuTinte 
u\ 
ffe 
but in the interest of scientific progress I have attempted tt, .s 
■ 
♦ Bell, American Journal of Science, May, ISSS. p. '^O^- 
