Astronomical Discovery. 67 



The Academy concluded this sitting by going into a secret 

 Committee for several objects of internal administration; and 

 in particular for the consideration of some arrangements neces- 

 sary to expedite the publication of their Memoirs. 



April 5. — M. James Leroy claimed the priority of inven- 

 tion of the instrument above mentioned, for effecting the de- 

 struction of stones in the bladder. — M. Seligne presented an 

 achromatic microscope of his invention, which was referred to 

 a Commission. — M. de Humboldt gave some new information 

 of MM. Boussingault and Mariand de Rivero, who continue 

 to explore the environs of Bogota with equal zeal and success. 



XI. Intelligence and Miscellaneous Articles. 



ASTRONOMICAL DISCOVERY. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 | HAVE this moment received a letter from a distinguished 

 •* astronomer on the continent, announcing a very happy and 

 brilliant discovery, or invention, by M. Bessel, for determining 

 the accuracy of the position of his meridian circle. It is well 

 known that the method of observing by reflexion has been, for 

 nearly half a century past, practised on the continent; al- 

 though but recently introduced into this country. In this 

 method, the observations themselves are made the test of the 

 position of the instrument. But M. Bessel's inquiries were 

 directed to some mode by which he might be enabled to de- 

 tect any flexure in his instrument, without astronomical obser- 

 vations ; and, of course, in any state of the atmosphere, whether 

 cloudy or otherwise. This question was obviously reduced to 

 the finding of two points, which, being seen from the centre 

 of the meridian circle, are exactly 180° distant. These points 

 he determined by the method given by M. Gauss in M. Schu- 

 macher's Astron. Nach. No. 43, and from the property of the 

 telescope there alluded to. 



As M. Bessel's method will be fully explained in one of the 

 ensuing Numbers of M. Schumacher's Journal, and as I have 

 not time at present to be more explicit, I shall now only give you 

 an outline of the plan. M. Bessel places two telescopes (each 

 furnished with micrometer wires) in the two apertures of the 

 building, with their object-glasses turned towards each other : 

 one on the north, and the other on the south side. Let us 

 call these telescopes A and B. He then takes the glasses out 

 of the meridian circle, so that he might see (through the tube 

 of the instrument) with the telescope A, the intersection of the 



I 2 wires 



