NO. 1865 OUR knowledge; of the sun — HALE 359 



black paint. The corresponding area is inversely proportional to 

 the measured amount of light, from a source of known intensity, 

 which is transmitted by the blackened plate. 



In practice, the investigation has been planned so as to permit 

 the determination^ not only of the total area of the calcium flocculi, 

 but also their distribution in latitude and longitude. For this pur- 

 pose the points on the solar negative corresponding to the intersec- 

 tions of meridians and parallels 10° apart are marked on the glass 

 side with the heliomicrometer, which is provided with an electrical 

 marking pen for this work. The area of the flocculi lying within 

 each square, 10° on a side, is then measured. The sum of these 

 areas gives the total area of the calcium flocculi for the date in 

 question, while the values obtained for the individual squares per- 

 mit the variations in solar latitude and longitude to be studied. In 

 order to avoid errors incident to the measurement of areas at points 

 near the Sun's limb, the region investigated is confined to the middle 

 of the Sun's disk and extends 40° east and west, and 40° north and 

 south, from the central point. 



A large number of photographs have been measured in this way at 

 the Solar Observatory, and in the course of time it will be possible 

 to learn whether these results indicate any significant relationship 

 between solar and terrestrial phenomena. 



Conclusion 



I trust this account of recent investigations will make clear some 

 of the means at present employed to extend our knowledge of the 

 Sun. Every advance in this department must contribute toward 

 the solution of the great problem of stellar evolution, as well as the 

 lesser problem of the solar constitution. The latter is of special 

 interest to the inhabitants of the Earth, since our very lives depend 

 upon the constancy of the solar radiation, and thus upon the mechan- 

 ism which maintains it. But the problem of stellar evolution is 

 of even greater philosophical interest. As the biologist withdraws, 

 one by one, the veils which enshrouded the mysteries of organic 

 development, and as the paleontologist reconstructs for us the life 

 of former times, the desire to learn of the earliest steps along the 

 great highway of evolution must grow in every intelligent mind. 

 Fortunately the problems of the astronomer, difficult though they 

 be, are more open to attack than those which confront his biological 

 colleague. With the powerful telescopes and spectroscopes of the 

 present day, and the climatic advantages which well-placed mountain 



