ox A TABLE OF STANDARD WAVE LENGTHS OF THE SPECTRAL LINKS. 118 
4th. The series of photographs containmg coincident spectra, iiioslly on jilih .s 90 
short as to make the spectra nearly normal, were now introduced. The pklcs 
were numbered from 1 to 20, Nos. 7 and 19 being rejected becnn*»c Imperfect. 
This series of plates were obtained by pliotographlng a, narrow strip of ona 
spectrum between two strips of another, the overlapping spectra being scpnrnt.-d 
by absorption. In order to eliminate any change in the apparatus during the 
* 
exposure, the latter was divided into three parts, the first and Ihird being gi\en 
to the same spectrum. 
F 
This series of plates gives me a continuous series of pliofograpli< from wave h'ugth 
7200 to the extremity of the ultra violet spectrum, each part being inlcruov^.. wIlli 
one or two other parts of the spectrum. Thus, wave length 3900 comes from ^2^0 
and 5850 with only a slight difference in values. There is srnrcely any different a 
in any wave length as derived from any portion of the spectrum; thus proving tlie 
accuracy of the whole table. The description of the plates is as follows. 
PEG TOG RAP niC COINCIDENCES. 
Concave Grating 10,000 Lixes to the Ixrn. 
Spectra. Plate. 
Standard. 
1 4407 to 4643 and 3331 to 3486 /, f; 
" 2 4637 " 4890 " 3478 " 3007 h,J 
" 3 4823 « 5068 « 3612 " 3805 j\ k 
« 4 4919 » 5133 « 3C83 " 3875 y, h 
« 5 5050 « 5288 « 3780 " 4005 k, ? 
6 5097 « 5333 " 3821 " 4157 h ^ 
U 
7 
' « 8 5242 " 5477 " 3937 » 4121 I, m 
(( 
9 5405 " 5662 « 4073 " 4222 m, n, e 
" 10 5582 « 5816 « 4293 " 4376 «,/ 
11 5782 « 5934 " 4343 « 4447 o,/ 
U 
ii 
12 4157 " 4267 « 3129 « 3218 « 
13 4157 « 4325 " 3094 " 3246 e 
14 3218 » 3318 
15 4391 " 4643 « 3292 " 3478 /, ^ 
I 16 5788 « 5977 " 3864 « 3977 o 
a 
u 
u 
17 5788 « 5977 " 3S64 « 3984 o 
18 5715 « 5977 « 3875 » 3977 o 
« 19 
^ 20 5853 » 6509 " 3024 "320^ o,r,q 
Plates 7, 14, and 19 were imperfect, owing to clouds pa««in..^ over the sun, 
although a i)art'(3218 to 3318) of Plate 14 was used for interpolation,. as observa^ 
tions were scanty in that region. 
