208 LIGHT SCIENCE FOR LEISURE HOURS. 



ask those readers who do not care to make the calcula- 

 tions for themselves, to accept on trust my statement 

 that 25m. 56s. would be the time required for the 

 upper half of our projectile's course. 



It is already obvious, therefore, that the matter 

 watched by Professor Young did not behave like a 

 projectile in vacua, having 200,000 miles as the limits 

 of its upward course. It traversed a space in 10 

 minutes which such a projectile would only traverse in 

 about 26 minutes. 



Now two explanations are available. We may 

 suppose that the real limit of the upward flight of the 

 hydrogen was greater than 200,000 miles, and that, 

 therefore, the 100,000 miles next below that level were 

 traversed with a greater velocity than would correspond 

 to the case we have just been considering ; or we may 

 suppose that the matter was in reality projected with 

 a much greater velocity than 200 miles per second, 

 and was brought to rest at a height of 200,000 miles 

 by the retarding action of the solar atmosphere co- 

 operating with solar gravity. And of course we may 

 conceive that these two explanations coexist, and that 

 the two causes considered operate with any degree of 

 proportional activity, between the relations which would 



A E the flight of a projectile. About centre C draw half circle A D L, 

 cutting half circle on E C as diameter in D. Draw D M square to A C, 

 and let M m L, a half circle on M L. cut K C in m. Then the time of 

 descent from E to any point P in HA is represented by the ordinate 

 P Q, (parallel to KC), where m C represents 18 min. 40 sec., which is 

 the time in which C A would be traversed, with a velocity of 379 miles 

 per second. 



