5 i2 POPULAR SCIENCE MONTHLY. 



definite connection between the number and size of the spots on the 

 sun's surface and the weather or climate on the earth. On the other 

 hand, theoretical reasons would lead us to expect some connection, and 

 the evidence is rather in favor of it than otherwise; but it is highly 

 probable that the direct effect of the spotted area is unimportant com- 

 pared with the effects produced in our atmosphere by other causes. 



Although a negative answer must at present be given to the question 

 whether sunspots have any considerable share in the variations of 

 climate, it would be leaving a wrong impression if no mention were 

 made of a well-established 11-year period in the variations of 

 another set of terrestrial phenomena. The state of the earth's mag- 

 netism has for many years been carefully recorded by suitable in- 

 struments and there is no doubt that its fluctuations correspond quite 

 closely with the state of the sun's surface, not only in the cycle of 

 long period, but also with respect to the minor variations. It can 

 not as yet be stated that the appearance of a group of sunspots always 

 causes a disturbance of the magnetic needle, but investigations have 

 been published and others are still under way which appear to show 

 a very intimate connection between them. Nothing is known as to 

 the causes of this connection. 



We have been dealing hitherto with only one exhibition of the solar 

 activity. It is one which catches the eye and is perhaps well adapted 

 to show the main features of this activity in somewhat the same way 

 as the presence of snow and ice would indicate the higher peaks of 

 a mountain range. Pursuing the simile, while it is true that we get 

 an idea of the more prominent outlines of the mountainous region by 

 noting the white places on the dark background, the latter would in- 

 clude many elevations and depressions which are never touched by 

 snow, and we can not have a correct idea of the range without finding 

 some method of observing them also. The case of sunspots is not 

 very different. They probably form the bolder outlines, but, as Pro- 

 fessor Bigelow has pointed out, they constitute but a sluggish register 

 of the solar activity. There is another set of variable phenomena, 

 known as the prominences, which are now supposed to furnish a much 

 better index of the state of the sun at any time. These are elevations 

 of the material of which the sun is composed, visible round the edge 

 of the disc, and they appear to be huge masses of liquid or gaseous 

 matter violently ejected from the main body. Unlike the sunspots, 

 prominences are rarely absent and some of them can nearly always be 

 seen on the edge of the sun's disc, so that by recording the number 

 and height of those observable from day to day a much more con- 

 tinuous and accurate series showing the activity of the sun can be ob- 

 tained. Moreover, it has been shown that the variations in the series 

 correspond much better with those in the earth's magnetic force than 



