14 ON THE APPLICATION OF INTERFERENCE METHODS 



The full cm-ve iu Fig. (ih, Plate IT., gives the ex])erimental result for the 

 visibihty at the luaxinia for yellow sodium, corrected for personal equation. 

 The dotted curve coiTespouds to th(^ formula 



F=2"'^''"*' cos 0.7 50 cos 0.1/140. 

 The complete equation, assuming that the two lines are alike, is 



V= 2-^'''»°*= cos 0.8 0.58 cos 0.7 50 cos 0.1 140. 



The interpretation of these results is that each of the sodium Unes is a 

 close double, as shown in Fig. Qa. 



The yellow-gi-een sodium hue at ). = 5687 is a double whose components 

 are about the same distance apart as the yellow pah-. It was foimd to be 

 far less variable than the yellow, and the full visibility curve, neglecting 

 slight in-egularities, gives the experimental results corrected for personal 

 equation. Fig. Ih, Plate 11., shows that its components are single and eoiTe- 

 spond in distribution of hght fau-ly well with the exponential curv^e, Fig. la. 



The same may be said of the orange-red double at G15G also, except that 

 this seems to have a companion of feeble intensity. 



The doubles at 5150 and at 4982 were also examined, the curves showing 

 nearly the same results as the red. 



Ziuc. The temperatui-e at which the radiations from metallic zinc 

 could be conveniently observed was in the neighborhood of the melting- 

 point of the glass of w^liich the vacuimi-tubes were made. But few obser- 

 vations were recorded, though these were quite consistent. The results 

 of the observations, corrected for personal equation, are given in Figs. 8 

 and 9, Plate II. The fonner is the record obtained from the red Mne near 

 6800, and shows that tliis line is single, the distribution of hght agreeing 

 very well with a simple exponential curve, the " hah"- width " being 0.013. 

 Tlie latter shows the results of obsen^ation on the blue line near 4811. 

 Tilt' dotted curve is the visibility cm-ve due to a distribution represented 

 in Fig. 9a. 



Ciiihiiiinn. .Metallic cadmium in tlir vacuum-tube at a temperatvu-e of 

 about 280° gives a number of very bright lines, widely separated, and vary- 

 ing very shghtly with temperatm-e or pressure. Fig. 10ft, Plate III., shows 



