vi PREFACE. 



This, of course, includes a complete cataloguing of the spots 

 which have been observed time out of mind, and also of 

 those solar prominences the means of observing which have 

 not been so long within our reach. It is of the highest 

 importance that these data should be accumulated, more 

 especially because it has been found that both in the case 

 of spots and prominences there are distinct cycles which, in 

 the future, may not only be very much fuller of meaning to us 

 than they seem to be at present, but may even satisfy the 

 representatives of the cui l)ono school. 



The second branch of the work is this : These various cycles 

 of the spots and prominences have long occupied the attention 

 both of meteorologists and electricians ; and one of the most 

 interesting fields of modern inquiry, a field in which very 

 considerable activity has been displayed in the last few years, 

 is one which seeks to connect these various indications of 

 changes in the sun with changes in our own atmosphere. 



The sun, of course, is the only variable that we have. 

 Taking the old view of the elements, we have fire represented 

 by the sun, variable if our sun is variable ; earth, air, and water, 

 in this planet of ours, we must recognise as constants. From 

 this point of view, therefore, it is not at all to be wondered at 

 that both electricians and meteorologists should have already 

 traced home to solar changes a great many of the changes with 

 which we are more familiar. This second line of activity 

 depends obviously upon the work done in the first, which 

 records the number (the increasing or decreasing number) of 

 the spots and prominences, and the variations in the positions 

 which these phenomena occupy on the surface of the sun. As 



