i3'2 PHILOSOPHICAL TRANSACTIONS. [aNNO 1/26. 



well as different degrees of foulness: on which account, the force communicated 

 to the pendulum would not be constantly equal, which would cause some small 

 alteration. But when the pendulum is very heavy, and vibrates in a small arch, 

 and the workmanship of all the parts is well performed, there will be very little 

 inequality in the motion, besides what proceeds from heat and cold. 



In making use of quicksilver for a pendulum, by varying the diameter of the 

 vessel that contains it, or the thickness of the rod of the pendulum, whether it 

 be of brass or steel, they may be reduced nearly to an equality as to the re- 

 ceiving, or retaining the impressions of heat or cold, on which the regularity 

 of the motion chiefly depends; and particular care ought to be used to free the 

 mercury from all blebs of air, otherwise their great and sudden expansion, or 

 contraction, may cause a considerable disorder ; but the air may as easily be 

 excluded in this way, as in a barometer, and the great specific gravity of quick- 

 silver renders it a proper material for the weight of a pendulum. 



De Salibus Alcalino-fixis, Auclore C. Neuman Chym. Prof. Reg. Berolin, R.S.S. 

 Pars reliqua. N° 3g2, p. 45. 

 See remark at p. 128 of this Vol. of these Abridgments. 



Several Celestial Observations maae at Southiuich, in the County of Northampton. 

 By George Lynn, Esq. N° 3g3, p. 66. 



The following observations were made at Southwick, long, west from London, 

 so', lat. 51" 58' nearly, with a 13-foot telescope, whose aperture was 2.4 inches, 

 and charge 2.5 inches ; all by apparent time. 



In 1724, Nov. 8, 7"^ 37"' 7% the first satellite of Jupiter began to emerge : 

 the same day at &" 24"" 20", the third satellite began to immerge. 



In 1725, July 21, lo'' 43"" 20% the third satellite immerged, that is Mr. L, 

 lost sight of it, at a little above a semidiameter from Jupiter ; but it began 

 sensibly to abate of its light above 3 minutes before. 



August gth, 11*' 5 1" 20% Mr. L. lost sight of the second satellite; but it 

 began sensibly to abate of its light about 1 minutes before. 



August 18th, 25™ 50% the first satellite immerged very near Jupiter's body. 



Oct. 1 1th, 6'' 21"" 45% the third satellite began to emerge, and was full 3^ 

 minutes before it was at its greatest lustre. It came out of the shadow about 

 half a diameter from Jupiter's edge. 



Dec. 26th, 5*" 51"" 12% the second satellite began to emerge. 



1725-6, Jan. 5th, 6'' 28"" 30% the third satellite began to emerge. 



1724, June 23(1, lO** 15"% Saturn followed a star (in Senex's Zodiac, but 

 without any distinguishing mark) 51^ of right ascension in time, and declined 

 from it south 40". 



June 25th, lo'' u'", Saturn followed the same star, 13* oi right ascension in 

 time, and declined from it south, S" or 4" only. 



