160 
As asymptotes are known up to now P, and $,, whieb both also 
occur in the Natrium system, which has been drawn on the adjoined 
plate. To the Sharp series, as we shall call all the series belonging 
to column II, the same thing applies. They too form a translation 
group, in which P,, P,, and P,, occur as asymptotes, with all three 
of which we meet again also for the Natrium. The translation group 
of the Diffuse series, which all belong to column III has as asymp- 
totes: P,, P,, P,, S,, and JS,, the four first-mentioned of which occur 
in the Na-spectrum. Column IV contains the Fundamental series, which 
have as asymptotes P,, SD, D, and F,. Only PD, and Ff; 
occur in the Natrium spectrum. | 
In ease one should object to the names of Diffuse and Sharp 
Series, because not all the lines of all the diffuse series are diffuse, 
and not all those of all the sharp series are sharp, we may also 
simply speak of D- resp. S-series. In this connection I will quote 
an expression of Hicks *): 
“Regarded from this point of view, we may look upon P as 
standing for positive, D for difference and S for semi’. 
To make clear the connection between the old and the new names, 
this table may serve: (see p. 161). 
If a series is composed of several components, they may be 
distinguished by accents, e.g. P, Do, P,' De, P,'De. In this it is 
worthy of note that the different components of the S-, D-, and F- 
series resp. belong to the same translation group. Only for the P- 
series it is slightly different. There the asymptote remains the same, 
but the curve for the two components has a somewhat different 
position. So $, Pr, which denotes the 2°¢ component of the principal 
series, belongs to the same translation group as P,'Pe, which group 
however, differs somewhat from that of the P-series. They occur 
both also for Natrium, but have been omitted on the plate for 
clearness’ sake. 
If we examine this plate, we notice first of all, that all the recorded 
curves were drawn off the same pattern curve, which consists of a 
thick brass plate, into which according to my data the curve: 
109675.0 
VTE i Sas 
has been incised in an exceedingly careful way, so that «= 1 is repre- 
sented by a distance of 4¢.m., while y= 10° 4! (A expressed in A.U.) 
has been taken so that 1 m.m. corresponds to a frequency 100. 
The other sides of the templet constitute the two axes of the system, on 
which the curve has been drawn. Both sides are provided with a 
IL. c. p. 96. 
