150 DISSERTATION SECOND, {.rAitr t. 



gland by Horrox, and his friend Crabtree, and by them 

 only. Horrox, who was a young man of great genius, had 

 himself calculated the transit, and foretold the time very 

 accurately, though the astronomical tables of that day gave 

 different results, and those of Kepler, in which he confided 

 the most, were, in this instance, considerably in errour. 

 H6rrox has also the merit of being among the first who 

 rightly appreciated the discoveries of the astronomer just 

 named. He had devoted much time to astronomical ob- 

 servation, and, though he died very young, he left be- 

 hind him some preparations for computing tables of the 

 moon, on a principle which was new, and which Newton 

 himself thought worthy of being adopted in his theory of 

 the inequalities of that planet. 



The first complete system of astronomy, in which the 

 elliptick orbits were introduced, was the Astronomia Phi- 

 lolaica of Bullialdus (Bouillaud,) published in 1645. They 

 were introduced, however, with such hypothetical addi- 

 tions, as show that the idea of a centre of uniform motion 

 had not yet entirely disappeared. It is an idea, indeed, 

 which gives considerable relief to the imagination, and it 

 besides leads to methods of calculation more simple than 

 the true theory, and Bullialdus may have flattered himself 

 that they were sufficiently exact. He conceives the ellip- 

 tick orbit as a section of an oblique cone, the axis of which 

 passes through the superiour focus of the ellipse, while 

 the planet moves in its circumference in such a manner, 

 that a plane passing through it and through the axis, shall 

 be carried round with a uniform angular velocity. It is 

 plain that the cone and its axis are mere fictions, arbitrari- 

 ly assumed, and not even possessing the advantage of sim- 

 plicity. The author himself departs from this hypothesis, 

 and calculates the places of a planet, on the supposition 

 that it moves in the circumference of an epicycle, and the 



