380 Astronomical Society. 



Distance of the two stars of Polaris (single measure) 18'40 

 Jupiter's Polar diameter (mean of 6 measures) 3 2 "54 



Equatorial do. do. 34*06 



Consequently ratio of diameters 1*0467 



Mr. Donkin laid on the table, for the inspection of the mem- 

 bers, an instrument made by M. Fatten (a pupil of Breguet's 

 at Paris) for determining the fractional part of a second of 

 time, in astronomical observations. This piece of machinery 

 is about 5 inches in diameter ; and somewhat larger than the 

 ordinary size of ship chronometers. The instant of observa- 

 tion is marked by a very fine point attached to a spring, which 

 (by means of a peculiar kind of ink) makes an impression on 

 the dial plate. The machine will go for five hours. It is im- 

 possible to enter into any further description of this ingenious 

 piece of mechanism, without the assistance of plates and nu- 

 merous references : but we hope the inventor will be induced 

 to lay the whole before the public, at no distant period. 



Prize Questions proposed by the Astrononomical Society of 

 London. 



This Society has just proposed the following prize questions, 

 to the consideration of astronomers and mathematicians : viz. 



1st. The silver medal. To any person, who shall contrive, and 

 have executed an instrument, by which the relative magnitudes 

 of the stars may be measured* or determined; and of which 

 the utility for this object shall be sufficiently established, by 

 numerous observations and comparisons of known stars. 



2d. The gold medal. For approved formulae, for determi- 

 ning the true place of either of the four newly discovered pla- 

 nets, Ceres, Juno, Vesta, and Pallas : within such limits as 

 the Council may think sufficiently correct tor the present state 

 of astronomy ; — such formulas in each case to be accompanied 

 with comparisons of the observed places at various periods. 



3d. The gold medal. For a new mode of developing the dif- 

 ferential equations for expressing the problem of the three bo- 

 dies, by which a smaller number of tables shall be required in 

 order to compute the Moon's place to the same degree of ac- 

 curacy as by any existing tables, and with greater facility. 



To be entitled to competition for the prizes, all answers to 

 the first question must be received before the 1st of February, 

 1826; to the second, before the 1st of February, 1827; and 

 to the third, before the 1st of February 1828. 



LONDON MECHANICS' INSTITUTION. 



It gives us much pleasure to state, that this important In- 

 stitution 



