166 Proceedings of the Royal Society of Victoria. 



Pressure of Air. 



The pendulums were swung at the ordinary atmospheric 

 pressure, which was shown by the barometer Neuman, No. 122, 

 having a correction of — 0'022. The extreme range from June to 

 the middle of September was from 29-4 to 30-4 inches. Pressure 

 and temperature readings were always taken, at intervals of about 

 one hour generally ; sometimes more frequently. 



Arc of Vibration. 



This was read on the arc scale in inches. In the earlier part 

 of the operations, the arc was read frequently, and several inter- 

 mediate coincidences were observed during a swing ; but later, 

 the arc was read only twice at commencement, being generally 

 about 0-65 inches, and twice at the end of the swing, being then 

 reduced to about 0-08 inches. 



Levelling. 



The planes of suspension were carefully levelled before the 

 pendulum was suspended, and again when the pendulum was 

 taken out of the cylinder. No other intermediate observations 

 of level were made; but the scale at right angles to the arc scale 

 was read for each swing. It was found that for pendulum No. 4 

 and No. 6 the reading of this scale was about 0*5, and remained 

 fairly constanc in both positions of the marked face ; but the 

 readings for pendulum No. 11, were about 0-9, for face "P" and 

 1-2 inches for face " JM". According to the level, the planes of 

 the three pendulums generally remained in good adjustment, 

 during each respective series of swings. Mr. Ellery invariably 

 placed the pendulums in and out, and changed the position of 

 the marked face when required. 



The Swings. 



Each pendulum was swung an equal number of times with its 

 marked face towards the observer, and towards the clock, the 

 first position being designated by face "M," and the second by face 

 " P." Twelve sets were observed for each pendulum ; six in each 

 position. The results for Pendulum No. 11 came out more 



