VOL. XLIX.] PHILOSOPHICAL TRANSACTIONS. 41 



orbis magnus from the syzygies with Jupiter to the quadratures, and subtracting 

 it in passing from the quadratures to the syzygies ; and then in any case 

 there will be had the true place of the earth's aphelion or the sun's apogee. 



In like manner will the variation of the moon be to the variation of the sun, 

 as the mean motion of the moon's apogee in the time of the moon's revolution 

 at the sun, is to the mean motion of the sun's apogee in the time of the sun's 

 revolution at Jupiter : and therefore, since the motion of the moon's apogee in a 

 synodic time is 3" 17' 20'^ and the motion of the sun's apogee is 14''' 15"', in 

 which time the sun revolves at Jupiter, putting the greatest variation of the 

 moon at 35' 10*, the greatest variation of the sun comes out 2''^ 32'", which 

 takes place when the sun is in the octants with Jupiter ; in other places the va- 

 riation will be to the greatest variation, as the sine of double the sun's distance 

 from his quadratures or syzygies with Jupiter, is to radius very nearly. 



Also, if the excentricity of the earth's orbit and Jupiter's were the same, the 

 equation of the mean motion of the earth or sun, which arises from the various 

 contraction and dilatation of the orbis magnus by the force of Jupiter, would be 

 to the like equation of the moon, as the motion of the sun's apogee in the time 

 of Jupiter's revolution, is to the motion of the moon's apogee in the time of the 

 sun's revolution, that is, as 2' 34'^ 4l"' to 40° 40' 43" : but this equation of the 

 sun should be augmented in the ratio of the excentricity of Jupiter's orbit to the 

 excentricity of the earth's orbit, or in the ratio of the greatest equation of Ju- 

 piter's centre, to the greatest equation of the sun's centre very nearly, that is, in 

 the ratio of 5° 3l' 36" to 1° 6' 20'' : hence if the greatest equation of the moon's 

 mean motion be 1 1' 50'^, the greatest equation of the sun's mean motion will be 

 2" 8'", viz. in Jupiter's mean distances from the sun. In other places it is pro- 

 portional to the equation of Jupiter's centre. In all these circumstances the force 

 of Saturn is neglected as insensible. 



ex. A Journal of the fVeather in Dublin for the Years 1753, 1754, 1755. j5y 

 James Simon, F. R, S., S. A. p. 759- 



This journal contains the register of the barometer, with the state of the 

 weather, as to wind, rain, snow, &c. for every day in the three years 1753, 4, 

 5, and that for three times in each day, viz. morning, noon, and night. 



CXI. An Account of what happened at Bergemoletio, by the Tumbling down of 

 Fast Heaps of Snow from the Mountains there, on March IQ, 1755 : As 

 taken by the Intendant of the Town arid Province of Cuneo. Received from 

 Dr. Joseph Bruni, Professor of Philosophy at Turin, and F. R. S. Commu- 

 nicated by Mr. Henry Baker, F. R. S. Translated from the Italian, p. 7g6. 



In the neighbourhood of Demonte, as in the upper valley of Stura, on the 



VOL. XI. G 



