68 SCENERY OP THE HEAVENS. 



the same time in the same direction, though at a slower pace. The planet accomplishes 

 an angular motion of 1 36' per day, while the earth follows at the rate of 59', and is thus 

 gained upon by only 37' daily. But the two planets will obviously appear to keep on the 

 same side of the sun, until Venus has gained half her orbit in advance, or 180. This it 

 will require about two hundred and ninety days to effect, as the difference of their daily 

 rate, 37' x 290= 10730'= 180 nearly. It will be seen from the diagram, that at the 

 time of the inferior conjunction, the unenlightened half of the orb is turned towards us. 

 Did she present in that position her illuminated side, we should see the planet as a small 

 brilliant moon, shining with twenty times her ordinary lustre, as she is then a hundred 

 and sixty millions of miles nearer the earth than when at the opposite point. As it is, 

 however, she is our best friend among the stars, the most radiant of the host, and has 

 been observed to cast a clearly defined shadow. 



This planet, like Mercury, transits the sun's disk, and then appears shorn of her beauty, 

 under the form of a dull dark spot. The first instance of the phenomenon being seen by 

 any human being occurred on the 24th of November 1639, under remarkable circumstances. 

 It was observed by two youthful friends ; Jeremiah Horrocks, at Hoole, near Liverpool, 

 and William Crabtree, at Broughton, near Manchester. The great credit in the observation 

 is due to the former of these individuals, who anticipated the event, and predicted the 

 time. Upon Keppler completing his tables in 1627, he predicted that Venus would pass 

 over the sun's disk on the 6th of December 1631. He died before the time arrived. The 

 transit was looked for, especially by Gassendi, but it was not seen ; and Keppler had distinctly 

 announced that it might not be visible in Europe, as the planet would not be in contact with 

 the sun till towards sunset. It is now well known to have taken place during the night 

 between the 6th and 7th. But Keppler had stated, that after this period Venus would not be 

 seen again upon the solar disk till the year 1761. This was an error. Horrocks suspected it on 

 going over the tables, and comparing them with others. Having repeated his calculations, 

 he found that Venus might be expected to enter upon the solar disk a little 

 before sunset, November 24, 1639. It appears that the time of the transit was nigh 

 at hand when the discovery was made, so that there was no possibility of giving general 

 publicity to the expected event, in an age when communication was very slowly main 

 tained. 



Though not doubting his own calculations, Horrocks did not deem it prudent to trust 

 implicitly to them. Accordingly, the day before the event was really expected, he watched 

 the sun at intervals ; but only ordinary appearances were noticed. The next day, a 

 Sunday, he attentively observed the solar image from sunrise till the hour appointed for 

 going to church " higher duties," as he remarks, " which might not be neglected for these 

 pastimes." Upon becoming at leisure, he resumed his observations ; and at a quarter past 

 three o'clock in the afternoon, his sagacity and industry were rewarded. " At this time," 

 he states, " an opening in the clouds, which rendered the sun distinctly visible, seemed as 

 if Divine Providence encouraged my aspirations, when, oh ! most gratifying spectacle, the 

 object of so many wishes, I perceived a new spot of unusual magnitude, and of a perfectly 

 round form, that had just wholly entered upon the left limb of the sun, so that the margins 

 of the sun and of the spot coincided with each other, forming the angle of contact." Owing 

 to the near approach of sunset, his time of observation was limited to about half an hour. 

 Meanwhile, in the neighbourhood of Manchester, the day opened inauspiciously, and 

 continued gloomy to a late hour in the afternoon. Crabtree had abandoned all hope of 

 being able to test the prediction of his friend, till just before going down below the horizon 

 the sun broke through the clouds. Repairing to the room where he had made his 

 preparations, he saw the round black spot with unspeakable delight ; and, according to 

 Horrocks, he was so struck with admiration at the spectacle, as to continue gazing upon 



