186 POPULAR SCIENCE MONTHLY. 



such changes it would be practicable to take several negatives at 

 about the same hour of each day, an actinometer being used, and the 

 exposures varied in accordance with its indications. The operations 

 might thus be omitted during bad weather, an additional number of 

 photographs being taken on succeeding fine days. Some very pleas- 

 ing views for the cinematograph could without doubt be obtained 

 by this mode of procedure. 



Turning now from the earth to the heavens, we shall see that 

 similar methods are applicable to the most prominent of celestial 

 bodies viz., the sun. The photographic art has long since been 

 applied with conspicuous success to the glowing solar disk, with its 

 dark spots and brighter patches or " f aculse " ; and such photographs 

 are now taken from day to day at leading observatories in various 

 parts of the globe. During recent years, moreover, astronomers 

 have contrived to photograph, under ordinary conditions, the sur- 

 roundings of the great luminary including the chromosphere and 

 prominences, but excepting the corona, which can not as yet be 

 studied in the absence of an eclipse. 



I shall not attempt to describe the many interesting features 

 shown in such photographs; nor is it necessary in this place to 

 indicate the precise means whereby solar picture films can be pro- 

 duced. The chief point to be noted is that changes often of a 

 rapid and striking character * are continually occurring both in 

 the sun's photosphere and its gaseous surroundings. The cinemato- 

 graph will enable us to actually see such changes taking place; and 

 it may be possible in this way to obtain new light on certain fascinat- 

 ing, though recondite, problems presented by the sun, while the com- 

 plex solar movements may in any case be pictured in a manner that 

 can not fail to prove deeply interesting and instructive. 



Although the common motion views are often described as realis- 

 tic, there are two respects in which they fail to correctly represent the 

 original scenes. Not only do they lack the charm of color (which 

 adds so much to the variety and interest of ordinary scenes), but the 

 effect of solidity, due to our binocular vision, is also absent. As re- 

 gards the reproduction of color, we shall have to rest content at 

 least for some time to come with monochromic views of ordinary 

 moving objects. Instantaneous photography in colors is not yet pos- 

 sible, nor is it likely to be achieved in the near future. In the color 

 process of M. Lippmann, for example, it is necessary to expose the 

 sensitive plates for relatively long periods of time. It may be ques- 

 tioned, also, whether such photographs could be successfully pro- 

 duced upon celluloid films. And even if these objections were re- 



* We are here concerned with movements which, though invisible to the observer's eye, 

 take place in reality with very great rapidity. 



