On the Bright Lines in the Spectrum of the Chromosphere. 377 



u slanting off obliquely on each side_, and presenting appearances 

 " which proved them to be waves of the critical length and cor- 

 " responding minimum speed of propagation. Hence the com- 

 " ponent velocity of the fishing-line perpendicular to the fronts 

 " of these waves was the true minimum velocity. To measure 

 " it, therefore, all that was necessary was to measure the angle 

 " between the two sets of parallel lines of ridges and hollows 

 ct sloping away on the two sides of the wake, and at the same 

 n time to measure the velocity with which the fishing-line was 

 " dragged through the water. The angle was measured by hold- 

 " ing a jointed two-foot rule, with its two branches, as nearly as 

 " could be judged by the eye, parallel to the set of lines of wave 

 " ridges. The angle to which the ruler had to be opened in this 

 " adjustment was the angle sought. By laying it down on paper, 

 " drawing two straight lines by its two edges, and completing a 

 " simple geometrical construction with a length properly intro- 

 " duced to represent the measured velocity of the moving solid, 

 " the required minimum wave-velocity was readily obtained. 

 " Six observations of this kind were made, of which two were 

 " rejected as not satisfactory. The following are the results of 

 " the other four : — - 



Velocity of moving Deduced minimum wave- 



solid, velocity. 



51 centimetres per second. 23*0 centimetres per second. 



38 „ „ 23*8 „ „ 



26 „ „ 23*2 „ „ 



24 „ „ 22-9 



Mean . . 2322 



" The extreme closeness of this result to the theoretical esti- 

 " mate (23 centimetres per second) was, of course, merely a co- 

 " incidence ; but it proved that the cohesive force of sea-water 

 " at the temperature (not noted) of the observation cannot be 

 " very different from that which I had estimated from Gay- 

 " Lussac's observations for pure water." 



XL VII, Preliminary Catalogue of the Bright Lines in the Spec- 

 trum of the Chromosphere, By C. A. Young, Ph.D., Professor 

 of Astronomy in Dartmouth College*. 



THE following list contains the bright lines which have been 

 observed by the writer in the spectrum of the chromo- 

 sphere within the past four weeks. It includes, however, only 



* From the American Journal of Science and Art for November, com- 

 municated in advance by the Author. 



