xxxviii KANT'S UNIVERSAL NATURAL HISTORY 



degree, and the great mathematicians eagerly 

 worked at the task. Euler published his Lunar 

 Theory (Theoria Motuum Lunae} in 1753 ; Clairaut 

 and D'Alembert also took up the question ; and 

 Tobias Mayer calculated Tables of the Moon, 

 which were transmitted to England, and which 

 were so favourably judged by Bradley that his widow 

 received ^"3000 on account of them in 1765. Clairaut 

 also published a set of tables of remarkable accuracy; 

 and the Berlin Academy, keeping watch over all 

 these mathematical efforts, published an annual 

 almanack embodying the latest results, which became 

 so popular that it was for a time the chief source of 

 the revenue of the Academy. 



But the Lunar theory was still complicated with 

 various difficulties, which were considered from every 

 possible point of view in connection with the re- 

 lations of the three bodies the Sun, the Earth, and 

 the Moon. In particular, certain inequalities in the 

 Moon's motion established then by observation, 

 brought great confusion and uncertainty into the 

 mathematical calculations. In the seventeenth cen- 

 tury Halley had already practically established what 

 i5 called 'the secular acceleration of the moon's mean 

 motion,' and it ever more urgently demanded investi- 

 gation and explanation of its cause. It was at this 

 point that a new question was raised in the Berlin 

 Academy, and set as the subject of a public prize 

 essay for 1754 ; and it was in connection with the 

 subject of this prize essay that Kant made known 



