1 88 A Short History of Astronomy [Cn vu 



expedition as soon as possible to capture them also, and 

 with that object to provide Kepler with the " sinews of 

 war " in order that he may equip a suitable army. 



Although the money thus delicately asked for was only 

 supplied very irregularly, Kepler kept steadily in view the 

 expedition for which it was to be used, or, in plainer words, 

 he worked steadily at the problem of extending his elliptic 

 theory to the other planets, and constructing the tables of 

 the planetary motions, based on Tycho's observations, at 

 which he had so long been engaged. 



143. In 1611 his patron Rudolph was forced to abdicate 

 the imperial crown in favour of his brother Matthias, who 

 had little interest in astronomy, or even in astrology ; and 

 as Kepler's position was thus rendered more insecure than 

 ever, he opened negotiations with the Estates of Upper 

 Austria, as the result of which he was promised a small 

 salary, on condition of undertaking the somewhat varied 

 duties of teaching mathematics at the high school of Linz, 

 the capital, of constructing a new map of the province, and 

 of completing his planetary tables. For the present, how- 

 ever, he decided to stay with Rudolph. 



In the same year Kepler lost his wife, who had long 

 been in weak bodily and mentalhealth. 



In the following year (1612) Rudolph died, and Kepler 

 then moved to Linz and took up his new duties there, 

 though still holding the appointment of mathematician to 

 the Emperor and occasionally even receiving some portion 

 of the salary of the office. In 1613 he married again, after 

 a careful consideration, recorded in an extraordinary but 

 very characteristic Better to one of his friends, of the relative 

 merits of eleven ladies whom he regarded as possible ; and 

 the provision of a proper supply of wine for his new house- 

 hold led to the publication of a pamphlet, of some mathe- 

 matical interest, dealing with the proper way of measuring 

 the contents of a cask with curved sides.* 



144. In the years 1618-1621, although in some ways the 

 most disturbed years of his life, he published three books 

 of importance an Epitome of the Copernican Astronomy, 

 the Harmony of the World^ and a treatise on Comets. 



* It contains the germs of the method of infinitesimals, 

 t Harmonices Mundi Libri V. 



