138 THE CHEMISTRY OF THE SUN. [CHAP. x. 



same way down to our milestones, we can give that velocity at 

 something like fifty miles per second. The wind velocities 

 measured in this way have amounted to 140 miles a second, 

 while the convection currents give us velocities which very often 

 amount to forty or sixty miles a second. 



This method enables us to determine a matter which a few 

 years ago we could not have determined in any other way. I 

 refer to the fact that the motions of the solar winds are to a 

 very great extent cyclonic. 



Eef erring again to the series of drawings (Fig. 55), it will be 

 seen that in the first of these drawings the hydrogen line indi- 

 cates by its change of refrangibility towards the red that the 

 gas is receding from us. In the third diagram we see that in 

 that part of the prominence the rays were being deflected to- 

 wards the violet ; that is to say, they were approaching us. In 

 the middle drawing, which represents what was seen when the 

 entire cyclone was included in the slit, we get indications both 

 of recess and approach. 



Now if anybody in the moon had as good a method as this of 

 measuring an earthly cyclone, he would see exactly this sort of 

 thing the part of the cyclone receding from him would give a 

 deflection in one direction, a complete view of the cyclone would 

 give him loth deflections, because he would get currents going in 

 both directions, and on the other part of the cyclone he would 

 get a deflection in the other direction. 



