290 Mr. A. A. Michelson on the Application of 



of this paper. At present it will suffice to take a particular 

 case — 'the pressure being very low, and the temperature about 

 250°*. 



The full curve in fig. 6 b, Plate V., gives the experimental 

 result for the visibility at the maxima for yellow sodium, cor- 

 rected for the personal equation. The dotted curve corre- 

 sponds to the formula 



V = 2~ x2/1562 cos -7/50 cos '1/140. 



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



V = 2~ x2/1562 cos -8/0-58 cos -7/50 cos -1/140. 



The interpretation of these results is that each of the sodium- 

 lines is a close double, as shown in fig. 6 a. 



The yellow-green sodium-line at \=5687 is a double whose 

 components are about the same distance apart as the yellow 

 pair. It was found to be far less variable than the yellow; 

 and the full visibility-curve, neglecting slight irregularities, 

 gives the experimental results corrected for personal equation. 

 Fig. 7 b y Plate V., shows that its components are single, and 

 correspond in distribution of light fairly well with the expo- 

 nential curve, fig. la. 



The same may be said of the orange-red double at 6156 

 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. 



Zinc. 



Tbe temperature at which the radiations from metallic zinc 

 could be conveniently observed was in the neighbourhood of 

 the melting-point of the glass of which the vacuum-tubes were 

 made. But few observations were recorded, though these 

 were quite consistent. The results of the observations, cor- 

 rected for personal equation, are given in figs. 8 and 9, Plate 

 V. The former is the record obtained from the red line 

 near 6360, and shows that this line is single, the distribution 

 of light agreeing very well with a simple exponential curve, 

 the " half-width h being 0*013. The latter shows the results 

 of observation on the blue line near 4811. The dotted curve 

 is the visibility-curve due to a distribution represented in 

 fig. 9 a. 



* The curve given above was obtained a year ago ; and since then it 

 has been impossible to reproduce it exactly. " 



