58 A CENTURY'S PROGRESS IN ASTRONOMY. 



pressed the view that the colour of a luminous 

 body must be changed by its motion of approach 

 or recession. It was obvious to Doppler that 

 if the body was approaching, a larger number 

 of light waves must be entering the eye of 

 the observer than if it were retreating. Miss 

 Clerke thus illustrates Doppler's principle : 

 "Suppose shots to be fired at a target at 

 fixed intervals of time. If the marksman 

 advances, say, twenty paces between each dis- 

 charge of his rifle, it is evident that the 

 shots will fall faster on the target than if 

 he stood still ; if, on the contrary, he retires 

 by the same amount, they will strike at cor- 

 respondingly longer intervals." It occurred to 

 various astronomers that it would be possible 

 to measure cyclones and hurricanes in the Sun, 

 not by change of colour in the spectrum, but 

 by the shifting of the lines ; and in 1870 this 

 was successfully done by Lockyer. In the next 

 few years efforts to measure the solar rotation 

 were made by Young, Zollner, and others, who 

 succeeded in measuring the displacement of the 

 lines, but not the time of rotation. This was 

 reserved for the famous Swedish astronomer, 

 Duner. 



Nils Christopher Duner > born in 1839 in 

 Scania, was employed as an assistant at Lund 



