Preface vii 



which modern astronomy has accumulated ; it would, for 

 example, have been easy to have filled one or more volumes 

 with an account of observations of sun-spots made during 

 the last half-century, and of theories based on them, but 

 I have in fact only given a page or two to the subject. 



I have given short biographical sketches of leading astro- 

 nomers (other than living ones), whenever the material 

 existed, and have attempted in this way to make their 

 personalities and surroundings tolerably vivid ; but I 

 have tried to resist the temptation of filling up space 

 with merely picturesque details having no real bearing on 

 scientific progress. The trial of Kepler's mother for witch- 

 craft is probably quite as interesting as that of Galilei 

 before the Inquisition, but I have entirely omitted the first 

 and given a good deal of space to the second, because, 

 while the former appeared to be chiefly of curious interest, 

 the latter appeared to me to be not merely a striking inci- 

 dent in the life of a great astronomer, but a part of the 

 history of astronomical thought. I have also inserted a 

 large number of dates, as they occupy very little space, and 

 may be found useful by some readers, while they can be 

 ignored with great ease by others; to facilitate reference 

 the dates of birth and death (when known) of every 

 astronomer of note mentioned in the book (other than 

 living ones) have been put into the Index of Names. 



I have not scrupled to give a good deal of space to 

 descriptions of such obsolete theories as appeared to me to 

 form an integral part of astronomical progress. One of the 

 reasons why the history of a science is worth studying is 

 that it sheds light on the processes whereby a scientific 

 theory is formed in order to account for certain facts, 

 and then undergoes successive modifications as new facts 

 are gradually brought to bear on it, and is perhaps 

 finally abandoned when its discrepancies with facts can 



