24-8 Prof. Encke on the Construction and Arrangement 



been led, from very peculiar circumstances, to communicate 

 what I write to the public. But in the work I have announced, 

 I will treat this subject fully ; and my critic will then see how 

 far he is mistaken in supposing that I wished to introduce the 

 consideration of particles attracting at very small distances. 



J. Ivory. 



XLIV. On the Construction and Arrangement of the New Berlin 

 Astronomical Ephemeris. By Professor Encke*. 



"W7"E observe the bodies of our solar system not from the 

 * ™ central point of their motions, but from a point on the 

 surface of the earth which has a double motion about this cen- 

 tral point. It would therefore be desirable to learn by the 

 ephemerides the position of the heavenly bodies with respect 

 to three points; — the centres of the sun, and the earth, and the 

 place on the terrestrial surface for which the ephemerides are 

 calculated. The peculiar modifications however, applicable 

 to every body in our system, are such as to leave no more than 

 two points for each of them, for which the more accurate data 

 are requisite. For the planets which are more distant, and 

 which are less regularly observed throughout the whole year, 

 the reduction from the centre of the earth to a definite point of 

 its surface is so simple, that nothing is required to facilitate the 

 calculation ; and for the sun and the moon, the relations to the 

 centre of the whole s}'stem disappear, being implied with re- 

 gard to the former, and unnecessary for the latter, whose course 

 is referred only to the earth. In every opening of the book 

 the two pages present, accordingly, for every body of our so- 

 lar system the polar coordinates with respect to two points ; 

 for the moon and the sun, those relating to the centre of the 

 earth and the place on the earth (Berlin) (with respect to the 

 latter point the distances, however, have been omitted, as un- 

 necessary); for the planets and the satellites of Jupiter, the 

 heliocentric and geocentric places, or that which will supply 

 their places. The coordinates which immediately involve the 

 results of the observations are referred to the equator, the 

 others to the ecliptic. The small planets make the only ex- 

 ception to this. The time which is everywhere applied, ex- 

 cept where it is expressly mentioned, is mean time. The be- 

 ginning of the day has been taken at noon, and the hours are 

 counted to 24; so that hours below 12 are those of the after- 

 noon, and the hours above 12 diminished by 12 h are the 



* From the New Berlin Ephemeris : being a translation of a portion of 

 the Appendix to that work, as promised in our Number for August, p. 145. 

 — Edit. 



hours 



