October, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



S6i 



he opened a new chapter in gravitation research, which 

 is more than his tradiicers were capable of doing ap- 

 parently. 



Gerard's Pendulum (1851). — Described as " horizon- 

 tal," but which had only one weight — about one hun- 

 dredweight block of granite — at the end of its rod. 

 The rod was a strong composite deal beam, provided 

 with a point at one end, and had the weight hung at 

 the outer end (see Fig. 7). A copper wire was fas- 



much as one-fifth of an inch." (Vide Edin. New. Phil. 

 Jour., 1853.) 



That pendulum repre.sents an important step in ad- 

 \ance, as regards obviating partially the uncertain 

 position of the real or virtual oscillation centre of 

 previous horizontal pendulums and of those classed as 

 such. 



Pcrroirs Pendulum (1862). — ^This was practically upon 

 Hengler's principle, but had, like one of his pendulums, 



Outlines showing principles of suspension or support of various kinds of Astronomical 



Pendulums, 



Class A. Vertical Pendulums. 



Fig. 



Fig. 2. 



Class B. Horizontal Pendulums (or Torsion Balances). 



Fig. 4. 



Class C. Inclined Pendulums (sometimes called Horizontal Pendulums). 



N.B.— The dotted lines in Figs. 6 to lo inclusive show the; 

 be understood to have the upper end of each axis I 



tcned to the weighted end of tlu' " rod." and the other 

 end of that wire was hooked into a ring fastened into 

 :i wall. The pointed end of the " rod " pressed against 

 that wall at a point nearly vertically below the ring. 

 I he rod was nearly horizontal, and took 15 seconds 

 to make one oscillation. The experiments were made 

 in a room, and diurnal changes of position were noticed 

 by means of an index moving over the surface of a 

 table. The maximum change .ippc.irs to have taken 

 place on a day "of bright sunshine." and was "as 



of Qscillaiion, and though they appear to be vertical, they must 

 ng forward out of the v ertical and towards the weight, usually. 



a separate stand. The chief difference was as regards 

 the materials used for suspending the rod and counter- 

 balancing the weight carried by "the rod. Other differ- 

 ences were merely of detail' or accessories. (Vide 

 Coniples Reiidus, \o\. 54, page 7J8, for results obtained 

 by its use.) 



^^ Close's Pc'iiduli/m.— The date of this is indicated in 

 " Barrett and Hrown's Practical Physics," published 

 in 1892, as being shortly before Zolln'er's, which latter 

 was invented about i87->. It consisted of a rod, having 



