348 



SCIENCE. 



[N. S. Vol. VIII. No. 194. 



lens, 5 inches in diameter, is placed in a 

 wooden box, which is mounted on an old 

 camera stand on rollers. It is not provided 

 with clock work. AVhen Janssen wishes to 

 make a photograph of the sun he wheels this 

 primitive afiair, stained and daubed with 

 nitrate of silver, from a shed on to a plat- 

 form, elevates it towards the sun, makes an 

 exposure with a rapidly moving slit, and 

 secures a photograph which, so far, but few 

 have approached in excellence. These pic- 

 tures are enlarged by a secondary lens in 

 the camera box to about twenty inches in 

 diameter. One peculiar feature of these 

 photographs is the frequent presence of 

 blurred regions, in striking contrast to the 

 generally exquisite sharpness of the granu- 

 lar surface. These disturbed regions are 

 believed by Janssen to be due to actual dis- 

 turbances on the sun's surface, and, there- 

 fore, to be true phenomena of the sun. I 

 have always had the impression that these 

 features are simply due to the presence of 

 small areas of bad seeing which are passing 

 at the moment of exposure ; that is, they 

 are the effects of small local disturbances 

 in our own air, such as every visual observer 

 is familiar with in night work. I remem- 

 ber having once secured a photograph of 

 the moon with the 12-inch of the Lick Ob- 

 servatory which showed just such a blurred 

 spot on its surface. This question could be 

 easily settled with a few exposures made a 

 minute or so apart, for if the blurred ap- 

 pearance repeats itself at the same point on 

 the sun's disc, then it can not be due to 

 local atmospheric disturbances. Doubtless 

 M. Janssen has long ago decided this ques- 

 tion, but, if so, it has escaped my notice. 



For the iirst successful photographs of the 

 sun's surface, however, we must return to 

 America. The first pictures to show this 

 granulation and the details of the sun spots 

 were taken by Lewis M. Ruth erf urd in 

 1870. These pictures were also made with 

 the collodion, or wet process. 



From the importance of a more thor. 

 ough understanding of the effects of the 

 sun upon the climate of the earth, daily 

 photographs of the solar surface are 

 made at a number of observatories, princi- 

 pally at Greenwich, Kew and in India. 

 These have been kept up for a great 

 many years. The Lick Observatory has 

 in recent years also taken up this sub- 

 ject. It is scarcely probable that a single 

 day goes by without photographs of the 

 sun being made at some one of these obser- 

 vatories. Thus a valuable record is kept 

 of the changes taking place on the solar 

 surface. Just what effect these sun storms 

 have upon the earth is not yet definitely 

 understood, but there seems to be an almost 

 certain connection between some of the 

 solar disturbances and terrestrial magnetic 

 storms, so that when the sun is violently 

 agitated a corresponding disturbance of the 

 earth's magnetism occurs. It is not yet 

 seen just how these disturbances may affect 

 the weather; so far the testimony seems in- 

 conclusive, and local conditions on the 

 earth may fully compensate for any effect 

 solar storms might have here. In the 

 meantime the work done in this connec- 

 tion at Greenwich and other places will 

 continue to grow in importance. One thing 

 that this repeated and constant photograph- 

 ing of the sun has proved is the non-exist- 

 ence of the so-called intra-mercurial plan- 

 ets, which before the days of photography 

 were so frequently seen transitting the sun, 

 by Lescarbault and many others. No 

 strange thing, aside from an alleged comet, 

 which was afterwards traced to a stain on 

 the photographic film, has been shown on 

 any of these photographs, with the excep- 

 tion, perhaps, of one of the sun photo- 

 graphs made in India which caught a 

 distant bird in its flight and showed clearly 

 its head and outspread wings projected 

 against the sun. 



Just as this continuous photographing of 



