1826.] making a minute Survey of the Heavens, 129 



any observations that he may have had an opportunity of 

 making, — such as errors of the pen, or of the press, in Hsts of 

 observations, — on stars observed, but no longer existing, — on 

 variable stars, &c. &:c. — will be published in the Memoirs of the 

 Academy. 



The Academy entertain no doubt that the fact of being able 

 to promote, without any expensive apparatus, such a great and 

 useful undertaking, as well as the prospect of discovering new* 

 planets even during the construction of the charts, will be suffi- 

 cient to excite the friends of astronomy to participate in it. 

 Nevertheless, it has been thouo;ht proper to announce a reward 

 of 25 Dutch ducats for the author of every chart made according 

 to the plan. 



As the Academy enjoy the privilege of free postage within 

 the limits of the Prussian post, astronomers in addressing the 

 members of the committee, or in sending in their charts, 

 may take advantage of this circumstance. 



Berlin^ \st November^ 1825. 



Letter from M. Encke, to J. F. W, Herschel, Esq. 



Berlin, May. 19, 1826. 



I hasten to answer the letter of the 29th April which you 

 were so good as to send me. I set too great a value on the in- 

 terest which the Astronomical Society takes in our plan, to delay 

 for a moment giving you all the explanation that you wish for. 



The principal object of the Academy is to procure a know- 

 ledge of the heavens as perfect as the present instruments wilt 

 enable us to obtain. If in Flamsteed's time we might content 

 ourselves with possessing maps of all the stars as far as the fifth 

 and sixth magnitude, it appears that at the present period we 

 cannot even limit them to those of the seventh and eighth mag- 

 nitude, but ought to extend them, so as to include in the same 

 sheet all the stars of the ninth magnitude. Or at least, the con- 

 tinual use w^e make of such stars renders it desirable to possess 

 observations sufficiently correct of all the stars as far as the 

 ninth magnitude inclusive. If we wish to observe such stars in 

 the same manner as Lalande has done in his llistoire Celeste, or 

 Bessel in his Zones, we could never be certain of having ob- 

 served them ally their number being too great. It seems, then, 

 that we should first of all endeavour to procm-e a knowledge of 

 the whole of the above-mentioned existing stars, more detailed 

 than that which can be obtained by an instrument fixed in the 

 meridian. Afterwards we may propose to make on each of 

 those stars the necessary observations, in order to assign more 

 accurately its true place. 



Such then is the object of the new astronomical maps. Tfiey 

 Nev^ Series, vol. xii. k 



