making a mimtte Survey of the Heavens. S3 



tjeal more difficult, and requires a more scrupulous attention 

 than the computation, where the two columns of the values of 

 Jc and d follow a regular order, and the other two columns, k\ 

 and a 1 ', have never much influence on the result. Each sheet 

 will represent two thousand observed stars at least: every one 

 of which will have its mode of delineation prescribed accord- 

 ing to its magnitude and the number of observations. It will 

 not be possible to commit this operation, which cannot even 

 be easily verified, to any other perso?i than the astronomer him- 

 self; who by putting his name to the sheet will render himself 

 responsible for the accuracy of his work. It is highly pro- 

 bable that many errors, both of observation and of writing, 

 will be made amongst that immense mass of stars which are 

 observed only once. If the astronomer himself makes both 

 the reduction and the drawing, he will be able to find out the 

 cause of such errors more easily than if the whole were com- 

 puted and arranged by another hand. In fact the execution 

 itself of the drawing will render the person, who undertakes 

 it, so well acquainted with the region he describes, that it will 

 very much facilitate to him the accomplishment of *he remain- 

 ing part of the work, which consists in noting down the stars 

 (down to the 9th and 10th magnitude) not yet observed. I 

 think that the reduction and the drawing of the stars already 

 observed, (made in such a manner that one may be certain 

 that each star in the heavens corresponds to its place on the 

 chart, which can only be obtained by making a revision of the 

 heavens,) is about half of the whole work, and that this is also 

 the part that has the greatest influence upon the general ac- 

 curacy of the whole. 



These are the principal motives which have induced the 

 Academy to propose the plan in the manner they have done 

 in the Prospectus. The Academy could not, as a body, itself 

 undertake so extensive a work, and thereby render itself in 

 some measure responsible for its accuracy. These maps will' 

 form part of the Memoirs that are published by the Society. 

 Each member will be answerable for his own portion, and the 

 duty of the Academy can only be that of committing this work 

 to persons who have already given proof of their being able 

 to fulfill the task which they engage to undertake. It is on 

 this account that you will find, in the Prospectus, that the 

 Academy have determined that the name of each author shall 

 be put on his map. This is the best proof, that they do not 

 mean to render themselves responsible for the correctness of 

 the maps, as far as the authors are concerned : but that they 

 intend only to defray the expenses,- — to encourage astrono- 

 mers by prizes,— to pay attention that a perfect conformity be 



kept 



