Physical Constitution of the Sun. 321 



liquid is situated at a depth of h = 8" below the visible edge of 

 the solar disk. H signifies the elevation of a protuberance 

 reckoned from the plane of the outlet. 



Let t signify the time which the prominence requires to rise 

 from the outlet to the height H ; 

 Tj the time which the protuberance needs to rise from the 

 height h (that is, from the visible limit of the photo- 

 sphere) to the height H ; 

 v the velocity at the outlet ; 

 v x the velocity at the height h. 



Assuming the truth of the first hypothesis, and neglecting the 

 diminution of the intensity of gravity (g) 3 we obtain the follow- 

 ing equations : — 



V 9 v 9 



v= V2gH, *!= V^(H-A). 



If we now take 



H = 64,370,000 metres, h = 5,722, 600 metres, #=274*3 metres 



we have 



t =11 minutes 25 seconds, 



Tj = 10 minutes 54 seconds, 



v =187,900 metres =25*32 German geog. miles, 



v v =. 179,400 metres =27*17 German geog. miles. 



If, therefore, we observe in a protuberance an ascensional ve- 

 locity equal to the above, we are entitled to employ in our equa- 

 tion the elevation which is reached in the above times. I have 

 often observed such a velocity in a protuberance, and have drawn 

 a representation (Plate II.) of a protuberance in which the 

 rate of ascension agrees well with the calculated velocities* ■ 



As regards the enormous initial velocities of these eruptive 

 movements, Lockyer, by his beautiful observations of the altera- 

 tion of the refrangibility of light, came by direct observations to 

 numbers of the same order. During the short period during 

 which these observations have been made, Lockyer* has ascer- 

 tained that the maximum values of the rate of motion, horizontal 

 and vertical, of a current of hydrogen in the chromosphere reach 

 40 and 120 miles per second. The above values expressed in 

 English miles are 



v = 123*1 miles, and t\ = 117*7 miles; 

 and therefore they agree with Lockyer's observations. 



* Proc. Roy. Soc. 1869, No. 115. 



