1 78 On the Passage of the Moon across the Pleiades in 1 SS9. 



ard declination the same length ; I have here used the pro- 

 portion of 5B to 60, which I believe is not far from the truth. 

 If a circle of paper l/^ inch in diameter be passed across the 

 chart so that its centre may traverse the dotted line, it will 

 readily be seen what particular stars the moon will cover, as 

 well as the order in which they will disappear. 



The Nautical Almanac gives the time of immersion, emer- 

 sion and near appulse of eight of the principal stars, at Green- 

 wich, as under : 



At S*" 6"" — No. 7 or i immerges. 

 8 9 — No. 6 or g immerges. 

 8 39 — No. 14 or c immerges. 

 8 44 — No. \0 o\- c immerges. 



8 57 — No. 10 or <? emerges. 



9 4 — No. 7 or b emerges. 



9 5 — No. 6 or g emerges. 



9 9 near appulse of the moon's southern limb to 



No. 20 or d. 

 9 17 — No. 37 or jj immerges. 

 9 28 — No. 14 or c emerges. 



10 — No. 51 or h immerges, and No. 37 or >j 

 emerges. 



10 17 near appulse of the moon's southern limb to 



No. 50 or /. 

 10 36 — No. 51 or h emerges. 



Mr. Baily observes, that not only has the passage of the 

 moon across the Pleiades at all times attracted the attention 

 of astronomers, but that it is now more particularly interesting 

 as affording a favourable opportunity for illustrating the theory 

 of Cagnoli, with respect to his mode of determining the figure 

 of the earth by means of occultations of the fixed stars. To 

 which I will only add, that a more complete concurrence of 

 favourable circumstances for this purpose can hardly be hoped 

 for than that which the passage of the 1 9th of March pre- 

 sents. The small portion of the moon's disc which will be 

 illuminated, her high northern declination, and her path so 

 directed as to cover nearly the greatest number of stars possi- 

 ble, is a happy coincidence, which I am sorry to say we shall 

 not meet with in any of the other passages of this year, and 

 which, indeed, many years may pass before it occurs again. 

 Wishing that we may be favoured with the only remaining, 

 but most important desideratum, a cloudless sky, 



I remain, Gentlemen, yours, &c. 



Swindon, Feb. 8, 1839. JaMES GroOBY, 



