18M.] Imperial Institute. 151 



exudation on the perosteum, then the cartilage is formed in which 

 the bony matter is gradually deposited. The deposition is reticu- 

 lated, owing to the nature of the substance in which it takes place. 

 The Society adjourned to Thursday the 10th of November. 



IMPERIAL INSTITUTE OF FRANCE. 



Account of the Labours of the Class of Mathematical and Physical 

 Sciences of the Imperial Institute of France during the Year 1813. 



(Continued frem p. 74.) 



M. Mathieu, an astronomer attached to the Imperial Observatory, 

 has presented to the Class two memoirs, one on the solstices, the 

 other on the latitude of the Imperial Observatory. These two 

 points had been discussed and established from a considerable series 

 of observations, by the author of the tables of the sun, and of the 

 base of the metrical system. The circles which Mechain and him- 

 self had employed in these observations, were those of Borda. It 

 is known that the indefinite multiplication of angles offers to the 

 patience of th^ observer a method of diminishing at pleasure the 

 error of the result. But it was feared, that the small magnifying 

 power of the telescope might have occasioned errors, which being 

 nearly the same for each observation taken apart, would not offer 

 the necessary compensation. It was thought necessary to possess 

 an instrument of a greater radius, which would at least diminish 

 the trouble of the observers, lead with less labour to the same pre- 

 cision, and furnish an important verification ; or probably even add 

 to the accuracy of the result. This wish of philosophers was ful- 

 filled by M. le Comte Laplace, who having obtained a circle of 

 Reichenbach, made a present of it to the Imperial Observatory. 

 M. Arrago and M. Mathieu were charged with the verification of 

 these points, the most delicate in astronomy. They have already 

 made a long series of observations of every kind. M. Mathieu 

 calculates them, and lays before the Institute the most remarkable 

 results drawn from them. 



The magnifying power of the telescope enabled them lo distin- 

 guish the pole star during the day. With the circle of Borda it 

 was scarcely visible in the twilight, and its diameter was smaller 

 than that of the micrometer wire. When the wire covered it, 

 there was no means of knowing if it was equally distant from its 

 two edges. Hence the observation might easily be wrong a second. 

 On that account, observations made during the night were pre- 

 ferred, because then the star touched the wire on both sides. With 

 the telescope of Reichenbach it is quite the contrary. The wire is 

 so fine, that at night the star greatly exceeds it in diameter. One is 

 less sure of being able to divide it by the wire exactly into two equal 

 parts. The excess is much smaller during the day, and hence 

 observations made at that time are more to be depended on : not- 

 withstanding this small disadvantage, the nocturnal observations 

 ugree as well as the others. The difference of all the observatiou 



