162 On the Occuliations of ike Fixed Stars. 



our present catalogues are so incomplete, that they by no means 

 contain all the stars that lie in the moon's path. An atten- 

 tive observer may therefore probably witness many occulta- 

 tions that are not recorded in this list. It may also be proper 

 to remark that M. Inghirami rejects f: om his list of ccculta- 

 tions, all those of the small stars, except such as take place 

 within a few days of the 7ic'-di moon : anil that," throughout the 

 whole of each lunation, he has inserted only stars of such a 

 magnitude as may render it probable they will be visible when 

 close to the moon, on the day on which the occultation takes 

 place. 



In a former paper on this subject, 1 remarked " that occul- 

 tations of fixed stars by the moon, as far as the fourth magni- 

 tude, are easily observable at sea ," but I have been since in- 

 formed that occultations of stars, as low as the seventh mag- 

 nitude, have been, under favourable circumstances, frequently 

 observed at sea. It may therefore be worthy of the considera- 

 tion of the Board of Admiralty, whether they will direct that 

 such lists should in future be annually made for the use of 

 navigators and others. The labour of computation cannot be 

 very great, if we bear in mind the rapidity with which the 

 present list was formed : the whole being computed, copied, 

 and sent off, in less than ten days. It is true that the calcula- 

 tions are correct to only 2 or 3 minutes of time : but this is 

 sufficient for the announcement of a phenomenon, which must 

 vary (as to time and other circumstances) at every point of the 

 earth's surface. 



It has been urged, in opposition to the printing of such a 

 list, that the best mode of announcement is to sweep the heavens 

 with a telescope, in the line of the moon's path: but this can 

 seldom be done with sufficient accuracy. We are frequently 

 deceived, as to the true course of the moon's apparent motion, 

 in those small distances (depending frequently upon parallax) 

 which decide whether an occultation will or will not take place : 

 much time is occupied in such observations, which might be 

 more usefully emplojed : and the observer is frequently wearied 

 out with such a doubtful, tedious, and oftentimes useless pur- 

 suit. Moreover, not knowing the pi'ecise point to which he 

 should direct his telescope, he may, under some circumstances 

 (such as during twilight or thin flying clouds), miss the obser- 

 vation entirely. 



It sometimes happens that the light of the moon will pre- 

 vent the star (particularly if it be of small magnitude) from 

 being distinctly visible. This inconvenience may in a great 

 measure be obviated by placing an opaque body in the joctis 

 of the object-glass, so as to cover nearly half the field of view ; 



and 



