AN ECLIPSE EXPEDITION TO SPAIN 



557 



in the earth. This terrestrial magnetism is evidenced through changes 

 in the compass needle, in frequent magnetic ' storms/ and in the beauti- 

 ful northern lights. The sun spots are thus the seat of some great 

 solar activity of whose exact nature we are at present not sure. 

 Moreover, the sun is not sending to the earth a constant amount of 

 heat. Very recent observations in Washington show that these solar 

 fluctuations are followed very closely by variations in temperatures all 

 over the earth. Whether these newly discovered variations in the sun's 

 heat are connected with the spots on the sun, or not, it is too early to 

 sa} r , but it may not be outside the bounds of possibility to be able in 

 the future to forecast the great variations in our earthly temperatures 

 from observations on the sun. We realize, then, the importance of 



North Gate, Daroca. 



these observations on the sun, and it is for the solution of problems such 

 as these that eclipse expeditions are sent out. 



To investigate the corona, photographs are taken of all sizes. The 

 diameter of the sun on the photograph depends on the length of the 

 camera, the greater the focus the larger the sun. At Daroca the 

 largest camera used was forty feet in length, which gave an image of 

 the sun four inches in diameter. In photographing, the lens can be 

 mounted pointing directly at the sky, or else the whole instrument can 

 be placed horizontally and light be reflected into it by means of a 

 mirror. We adopted the latter way as being the easier. 



The location of the eclipse camp was half a mile south of the town, 

 in the midst of a beautiful, fertile valley. From there, while we 



