French Katlofial Institute. 18t 



An extraordinary circumstance has given to this imper- 

 ceptible star tor a moment a more sensible diameter and a 

 stronger light. On the i?8th of May, the weather being 

 very fine, C. Messier was surprised to find in it a light 

 double to that which it had before ; and yet, according to 

 calculation, the distances of the sun and moon being 

 nearly the same, the brightness of the planet ought not to 

 have changed. The cause of this appearance was soon dis- 

 covered. The small planet in its course met with a star, to 

 which it appeared to be so close that the least interval could 

 not be o'bserved between them. Forty-two minutes after, 

 a separation took place, and, according to the known mo- 

 tion of the planet, the interval must have been 15". The 

 position of the small star may be determined at leisure ; and 

 from the repeated observations which may be made of it, 

 there will result for the moment of the observation of 

 ^Messier a determination of the place of the planet more 

 exact than any of those which could have been procured in 

 a direct manner. Those observations known under the 

 name of appulses are exceedingly I'are. However numerous 

 the small stars may appear, the intervals which they leave 

 between them are sufficiently large for the planets to make 

 the tour of the heavens without concealing one of them, or 

 at least anv of those which can be observed. The moon, 

 how ever, ought to eclipse some of them ever)' day : but 

 their faint lio;ht becomes extinct on the approach of a 

 stronger light ; and the observation of these eclipses is too 

 difiicult and too uncertain to induce astronomers to attend 

 to them: thev pay no attention but to stars of the 4th or 

 5th magnitude, and below. 



The arc of the meridian employed by the French astro- 

 nomers for determining the fundamental unity of the me- 

 tric system was the greatest ever measured, C, Mechain, 

 during his residence in Spain, remarked that it ccmld still 

 be extended two degreeii by forming two triangles, which 

 touching the coast of Spain between Barcelona and Turtosa 

 should terminate at the islands of Majorca and Ivica, The 

 difficulty was to measure the angles, and perceive in a 

 telescope not half a metre in length signals at the distance 

 of two hundred miles, These ooservations could succeed 

 only under the most favourable and consequently the 

 rarest circumstances ; thev could not l)c attempted but in 

 the middle of winter, and then they could have l)e(:n at- 

 tended only with half success, C Mechain found himself 

 obliged to abandon a project highly interesting, the plan 

 pf which was already drawn up. The reciprocal disposi- 

 M 3 lioita 



