14 HISTORY OF ASTRONOMICAL DISCOVERY. 



adopted the observed facts of planetary motion. The acute intellect of the ancients is 

 illustrated by the theories proposed ; but the lesson is strikingly furnished by their labo- 

 rious and abortive efforts, that it is folly to take for granted that which has not been 

 proved. The later Ptolemaists occupied themselves for centuries in amplifying and mend- 

 ing his system, supplying an epicycle here where it was wanted, and an excentric there 

 when required, and even converting his imaginary spheres into solid transparent wheels, re- 

 volving the one within the other, and each carrying a planet attached to it. The profound 

 of space was crammed with a succession of huge globular forms, in which the planets were 

 placed, all of the finest crystal, else the light of the stars had been intercepted ; beyond 

 these was the vast sphere of the fixed stars, crystalline likewise ; beyond that was iheprimum 

 mobile, incessantly rolling and giving motion by its friction to the spheres in its concave ; 

 while still farther out was the empyrean heaven, or paradise of blessed souls. 



The illustrious Alexandrian is not, however, to be identified with those who bore his 

 name in the middle ages. He would have repudiated at once their vain inventions. 

 They were schoolmen chiefly, more familiar with the dreamy philosophy of the Academy 

 and Stoa than with the experimental science of Hipparchus more skilled in logic than 

 in the examination of physical nature. The Ptolemy of the early Christian era was a 

 practical astronomer, and his merits as such give him a title to fame, which his theory, 

 now exploded and obsolete, ought not to obscure. He was the first to point out the 

 effect of the atmosphere in changing the direction of the rays of light ; and, though unable 

 to appreciate the amount of its refractive power, he clearly perceived its influence on the 

 altitudes of the stars, was aware of its increase with the distance from the zenith, and 

 assigned this as the cause of the greater apparent magnitudes of the solar and lunar discs 

 at the horizon an explanation now generally held. 



A scheme nearer to the truth than the Ptolemaic, commonly called the Egyptian, was 

 in vogue when the former was broached, though there is no reason to suppose, with some, 

 that it prevailed at an early period in that country. It regarded the inferior planets as 

 revolving round the sun, and moving, in conjunction with the sun, round the earth. It 

 is obscurely hinted at by Pliny ; but explicitly^ announced by Vitruvius, who lived a short 

 time prior to Ptolemy. Mercury and Venus, the architect remarks, are the planets 

 nearest to the rays of the sun, and move round the latter as a centre, appearing sometimes 

 progressive, sometimes retrograde, and occasionally stationary among the signs. But 

 this system, the prototype of the Tychonic, never became popular. A valid objection to 

 it was probably found in the fact that the inferior planets were never seen in phase, an 

 appearance which would be exhibited if alternately beyond the sun and between it and 

 the earth ; a position strictly true, and had the eye at that period been aided by the 

 telescope, Venus would have been seen in phase as at present. The superior planets 

 were invariably arranged by the ancients in the same order that which now obtains. 

 They had obviously no guide as to their respective distances from the earth, but the 

 indications discernible in their different brightness and velocity. Those which had the 

 slowest apparent movement were concluded to be the most remote. Hence Saturn, a 

 dull and sluggish traveller in space, was placed on the exterior ; then Jupiter and Mars 

 followed in succession towards the earth : the sun, moon, and inferior planets were placed 

 within the orbit of Mars, and the moon was considered the nearest celestial object to our 

 globe. Next to eclipses of the sun and moon, occultations of the stars and planets by the 

 moon, or the approach of the moon or of a planet to any star, with the appearance of 

 comets, attracted attentive observation. An occupation of Mars by the moon is men- 

 tioned by Aristotle, and one of Saturn is recorded by Ptolemy as having taken place in 

 the year 228 B. c. In fact, we may find some notice, more or less distinct, taken by the 

 ancients, of all the celestial phenomena which the unaided vision has observed in modern 



