Ih'poii oil the Grarlfi/ Stn-rr)/ of Australasia. 21.4' 



during the past year. Fortunati'ly the Royal Society of 

 London has forestalled the diseussion, and added ])enduluni 

 (11) to the two originally asked tor. The difticulty and 

 expense attending the constructicni of a new pendukini has 

 thus been avoided. 



E. F. J. Love, Secretary. 



Appendix. 



De.scription of the apparatus to be enn)hjyed in tlie 

 Gravity Survey of Australasia, by E. F. J. Love, iM.A. 



In drawing up a description of tlie a[)paratus, we may 

 consider se))arately, [a) the pendulums, {h) the clock, (c) the 

 vaciunn api)aratus and its accessories. 



{a) The pen<luhims are, undoubtedly, the most important 

 portion of the api>aratus. The three which it is pro))osed to 

 employ are all constructed of the same materials, and 

 practically identical, both in form and dimension. They 

 aie of the kind known as 'Invariable Pendulum." The 

 form is a flat bar of ])late brass 5 feet '1 inches long, 

 Ui3 ijich thick, and 1 7 inches broad, for a distance of 

 40 inches from the upper end. The remaining portion of the 

 bar, termed the "tail-piece," is lenticular in section, reduced 

 to a breadth of (VJ inch, and terminates in a point. Just 

 above the tail-|)iece is a tiat circular brass bob, G inches in 

 diameter and J-.S inches thick, which is fastened to the bar 

 l>y solder and i-ivets. The knife-edge is a prism of very hard 

 steel, adjusted per|)endicular to tlu^ plane of the bar, and 

 attached by means of a stout T head. It is 2 inches long, 



2o inch in height, and equilateral in secti<.>n, save that the 

 edge on which the (oscillations are performed is ground to an 

 angle of 120". The planes on which the pendulum oscillates 

 consist of two pieces of polished agate, ground true and set 

 in a heavy brass frame suppoi-ted on ver\- massive levelling 

 screws. Each })endulum has its own set of planes. 



All three pendulums are about 70 years old, and have 



1 teen repeatedly used for gravity survey work; in which 

 the}^ have given such consistent results as to warrant the 

 belief that the\' have reached a condition of api)roximate 

 e(|uilibrium as regaixls molecular change. For a statement 

 of their history, reference may be made to the " Re])ort of 

 the Great Trigont)metrical Survey of India," Vol. V, 

 Appendix \^. 30. 



