256 Prof. Encke on the Construction and Arrangement 



&' 



the well-known one of Bessel, is accompanied with the neces- 

 sary illustration of the manner of forming the argument It is 

 arranged by sidereal days. The other, which proceeds by 

 mean solar days, is more convenient, if, as is the case in obser- 

 vations of comets, a single position only of a star is required ; 

 as it is constructed after Gauss's general tables, and does not 

 require the calculation of the constants a,b 9 c,d. A small dif- 

 ference in the elements on which these tables are founded, which 

 has been noticed too late, causes a want of rigorous agreement 

 in the results ; but the difference never exceeding hundredth 

 parts of a second, it is of no consequence for practical pur- 

 poses. 



The last section contains the principal phenomena for ob- 

 servations. 



In the first place the eclipses of the moon and sun are suffi- 

 ciently described for determining the places on the earth where 

 they will be visible. For those who are fond of constructions, 

 the elements from which the phenomena may be determined, 

 have been added at the end. In future the solar eclipses, which 

 are interesting for our part of the world, will be treated rather 

 more in detail. 



Next follow the constellations of the planets. In these, re- 

 gard has been had to the two principal points of the elliptic 

 orbit, the perihelium and aphelium, the four principal elements 

 of the position of their heliocentric orbit, the two nodes, and the 

 maximum and minimum of their latitude, to the four principal 

 elements of their synodic paths £ 6 n , or those which corre- 

 spond to them for the sun and superior planets. 



I am not acquainted with any astronomical use of the con- 

 junctions of the moon and stars commonly given in astrono- 

 mical almanacs. It appears to me that the columns of right 

 ascension and declination of the moon render this part quite 

 superfluous ; as the arrangement of our present catalogues of 

 stars is such that there can be no trouble in determining the 

 stars near which the moon will pass. These have, therefore, 

 been omitted ; but, on the contrary, the possible occultations of 

 planets have been carefully investigated : and where there is a 

 possibility of an occultation, should it even not really take 

 place at Berlin, the conjunction has been noted. In the year 

 1830, Venus only will undergo an occultation at Berlin. 



In the present almanac for the year 1830, no occultations 

 of fixed stars by planets have yet been inserted ; as I enter- 

 tained doubt respecting the extent to which these investiga- 

 tions ought to be carried. An examination has proved that 

 no bright star down to the third magnitude will experience 

 such an occultation. I will leave it to the decision of astrono- 

 mers 



