1874.] Refracted and Diffracted Spectra. 29 
constant. The log. by which the relative wave-length y 
found by the calculation, is converted into the millimetric 
scale’of Angstrom is 2°5947234. 
The following are the values of e for the six principal lines 
of the spectrum, intervening between A and the more 
refrangible H, based on their positions in Kirchhoff’s index, 
and the formulated values of their wave-lengths relatively 
to that of H=1o. 
Index position. Log. of wave-length. Log. of log. Value of «. 
Bs)! 2593°r I°2420499 0°0941391 3°1516 
G50 69455 1°2223188 0°0871845 3°1963 
iD ro02;8 1°1757690 0°0703210 372322 
E. 1523°7 1°1269776 0°0519153 3°0057 
F. 2080'0 T°0919797 0°0382145 2°6244 
G. 2854°4 1°0394751 o’o168141 3°3636 
From the last column it will be perceived how variable is 
the value of «, and how erroneous must be any formula 
which is based on the assumption of its being constant— 
more especially if the constant be fixed so low as 2. 
The annexed table of the value of « has been calculated 
for every 10° of Kirchhoff’s scale, for the entire space 
between B and H. In the space between A and B, the 
observations are so few and uncertain that it has been 
found impossible to extend the table into this region with 
any degree of satisfaction. 
A careful examination of this table will show that, were 
the values of « graphically represented, they would form not 
a continuous curve, but a waved line—although in certain 
parts the line becomes straight. From 590 to rooo of 
Kirchhoff’s scale, the value of « gradually rises from 3°1516 
to 3'2342; but there isa slight interruption to the continuity 
of the ascent at 830 of the scale, where it has attained to 
3°2130. Here it remains constant for 5 terms, after which 
it falls slightly, becoming at 880 only 3'2040. It then 
ascends until, at 930, it reaches 3°2310, from which point 
there is a second fall, until at g60 it becomes 3°2210, whence 
it ascends to the maximum of 3'2342, which it reaches at 
1000 of the scale. 
From this maximum there is a continuous and more or 
less regular descent, until at 1980 of the scale the value of 
e is reduced to its minimum of 2°6150. From this point 
there is a continuous ascent to a second maximum at 3526, 
where « reaches the value of 3°4520. In this interval there 
are several points, at which « remains unaltered for several 
successive terms of the series. From 3526 of the scale 
