ON ASTRONOMY. 125 



DecemlDer 6, 1882. It may be expected that American astronomers 

 will take an important part in the observation of these transits. 



Of these two transits, that of 1882 will be the more favorable to an 

 exact determination. In a very interesting paper communicated to 

 the Royal Astronomical Society of London, in May, 1857, the astrono- 

 mer points out the special advantages which the United States will 

 possess for making accurate observations. 



In the first place, the two regions of country most favorable for 

 observation are the United States and a portion of the Antarctic land 

 discovered by Captain Wilkes, of the United States navy. In the 

 second place, we have a large number of observatories situated at 

 such convenient distances that any local cloudiness which might pre- 

 vent observations at some stations would not affect others. In the 

 third place,, we have the great and peculiar advantage of an extended 

 system of magnetic telegraphs by which the clocks and chronometers 

 of all the stations might easily be connected so that all the observations 

 might be made by one clock, say that of Washington. 



Humanly speaking, therefore, he remarks^ we may say that the 

 probabilities for the accurate and efficient observation of these phe- 

 nomena in the United States are vastly superior to any that could 

 have been reckoned on in any former time, or to any that could now 

 be anticipated in any other region. 



SIDEREAL ASTRONOMY. 



In my last lecture I discussed the methods of determining planetary 

 distances, first by finding the sun's distance from the earth, and then, 

 by means of Kepler's Third Law, computing the distances of the other 

 planets. The distance of the sun I stated to be 95,300,000 miles, with 

 a probable error of not more than half a million of miles. This pro- 

 portional error, and no more, will run through all the measures of 

 planetary distances. In this respect all has been done, or nearly all, 

 that can be done before the next transits of Venus in 1874, December 

 8, and 1882, December 6. 



I shall, this evening, invite your attention to the subject of Sidereal 

 Astronomy. A glorious and an inspiring sight it is to look at the 

 starry heavens. So vast, so brilliant, so pure, they seem to raise the 

 soul to diviner contemplations than any scene which pertains to earth. 

 The first impression on looking at the heavens is, that the stars are 

 absolutely innumerable, but on a more careful consideration we be- 

 come satisfied that this first impression is erroneous. If the attempt 

 is actually made to number them, it will be found that not more than 

 about 3,000 can be seen at any one time by the naked eye. The whole 

 number thus visible in the heavens does not probably exceed 6,000 

 or 7,000. 



Very early in the history of astronomy the stars were distributed 

 into groups called constellations, to which particular names were given, 

 depending upon some fancied resemblance between the configuration 

 of the stars and the form of the objector animal from which the name 

 was taken. Thus we have the constellation of the Great Bear, the 

 Little Bear, the Eagle, the Swan, the Lyre^ &c. These constellations 



