Wellington Philosophical Society. 453 



centre of the earth's shadow, as well as for day and night and seasonal 

 variations in temperature. 



(11.) That if compensation is made for a variation in the force of 

 gravity, as well as for a variation in temperature, the quantity of mercury 

 actually found necessary should be greater than the amount found sufficient 

 by calculation to compensate for variation of temperature alone. 



(12.) It is pointed out that the valuation of evidence is sometimes a 

 matter of great difficulty ; but it is hoped that the evidence afforded by the 

 facts brought out by the regulation of the Melbourne Observatory clock will 

 be considered clear. 



(13.) The Astronomer Royal of Victoria, and Assistant Astronomer, 

 kindly furnished the following information. The temperature of the clock 

 is obtained by maximum and minimum thermometers in or on the clock : — 



Weight of steel rod and fittings . . . . = T92 lbs. 



,, cast-iron jar . . . . = 4 - 38 ,, 



„ mercury .. .. .. =1600 ,, 



Diameter of jar (internal) . . . . . . = 2J inches. 



Length of jar „ . . . . . . = 8| ,, 



Half-swing of pendulum 1 deg. 58 minutes. 



A model of this clock, exhibited by the maker, Chas. Frodsham, was 

 exhibited at the Paris Exhibition, 1867, and found by the Horological Jury 

 to be one of the best in existence. 



(14.) The best authority on clocks then, SirE. Beckett, (Encyclo. Brit., 

 Art. " Clocks,") says that "a jar 2 inches in diameter requires the jar to be 

 filled with mercury to a height of 68 inches." The Director of the Obser- 

 vatory found that 8§ inches was not sufficient to compensate for variation of 

 temperature. The rate, however — a slightly losing one in summer, and a 

 gaining one in winter — seems practically perfect. 



(15.) In removing from the latitude of London to that of Melbourne 

 less mercury should be required. 



The paper concludes as follows :— 



"The foregoing shows that the astronomical clock at the Melbourne 

 Observatory has a quantity of mercury in excess of what is required to com- 

 pensate for changes of length of pendulum due to changes of temperature, 

 and that such excess probably compensates for variations in the force of 

 gravity. If the jar had been filled to a height of 6 - 8 inches with mercury — 

 the proper quantity to compensate for variations of temperature — then the 

 Melbourne clock would have been too slow in summer and too fast in winter, 

 this showing that the force acting on the pendulum — the force of gravity — 

 would be stronger in winter than in summer. 



" If the force of gravity is found to vary with the time of the year and 

 the time of day, then it is shown that the force of gravity is the action of 

 some physical agent. 



" The facts and reasoning go to prove that such is the case. Thus is it 

 shown that the physical causation of gravitation is probably discovered." 



2. "On the Occurrence of Bismutliic Gold at the Owen 

 Goldfields," by William Skey. 



Abstract. 



The author, after adverting to the f aet that in February last he had in a 

 paper to this Society announced the presence of metallic bismuth at the 

 Owen Goldfields, but in quantity so minute that the metal as metal was 

 invisible, went on to express the pleasure which he felt in being able to 

 exhibit to the Society metallic bismuth from the Owen in the nuggety form. 

 He then described the bismuthic gold (a sample of which was exhibited), 

 and concluded his paper by giving its approximate composition, promising, 

 however, a more extended and rigorous analysis as soon as further samples 

 were available for the purpose. 



