BEYOND THE RED IN THE SPEOTBUM — BABCOCK 175 



infra-red rays. The plate is exposed to these about 7 hours aiul 

 then developed in total darkness. Perhaps you can iiiia«;ine the 

 impatience with which the observer waits while the plate lixes sulU- 

 ciently to permit a glimpse in weak light to see whether he got 

 anything on it or not. 



It turns out that just twice as much of the solar spectrum can 

 now be studied by photography as in the day of Professor Rowland, 

 with the result that hundreds of spectral lines produced by atoms 

 in the sun's atmosphere are being accurately measured for the first 

 time. From what has been said about the significance of a line 

 in the spectrum it will be evident that such new data are valuable 

 to the physicist as well as to the astronomer. The physicist sees 

 in the sun's atmosphere a laboratory in which about two-thirds of 

 the elements known on earth are trying to tell him the story of their 

 structure. The astronomer sees new opportunities to examine the 

 constitution of our nearest star and so to understand what all stars 

 are like. 



Carbon is an element abundant in the earth. We should expect 

 it to be abundant in the sun also, since the best tests we can make 

 indicate that the earth is a fair chemical sample of the material 

 universe. Hitherto the only evidence for the presence of atomic 

 carbon in the sun has been found in nine faint lines in the visible 

 part of the spectrum. Although doubtless conclusive, this evidence 

 is not very impressive when compared to that for other equally 

 abundant elements. The fact is that throughout the visible and near 

 ultra-violet region, carbon atoms have no strong lines and only a 

 few w'eak ones. When studied in the electric arc, however, the 

 carbon atom is known to produce a group of very strong lines in the 

 infra-red. The new solar spectrograms show these same lines; but 

 since the accuracy here is greater than in the case of the electric 

 arc, the solar data more completely correspond with tlie predictions 

 of the atomic theory than do those of the laboratory. 



Perhaps we have talked of too many things in the course of the 

 hour, and some of them were not interesting to you. But, although 

 tiresome details may soon be forgotten, some general impressions 

 may remain. One which I should like to leave with you in closing 

 is that of the continuity of scientific progress. Some writers who 

 interpret scientific news in popular magazines and in newspaper 

 articles emphasize what they call the revolutionary discoveries and 

 theories of recent years. This no doubt attracts the eye of the 

 general reader, and at any rate reminds him that science is alive, 

 liut a much truer perspective is had by omitting just one letter in 

 such headlines and thus bringing out the fact that most important 

 scientific advances are evolutionary in character, not revolutionary. 



