PHYSICS. 581 



moir of Huygens, says that, iu consequence of the earth's rotation, a 

 peuduluin could not remain in the same plane during two consecutive 

 oscillations. De Sivry, in 1781i, in his translation of Pliny, observes 

 that the pendulum might be used in place of a compass, " the vessel in 

 turning about not altering by this motion the direction of vibration 

 once given to the pendulum." In 1837 Poisson, while admitting the 

 deflecting influence of the earth's rotation upon a projectile, denied the 

 possibility of any deviation whatever for the pendulum ; and in order 

 to sustain his opinion, he attempted to prove mathematically that the 

 component perpendicular to the oscillatory plane was too small to cause 

 any sensible deviation of the jjendulum from its plane, or to have any 

 appreciable influence on its motion. This opinion was refuted by Binet 

 and Plana iu 1851. Poncelet, in 1860, showed that the phenomenon 

 was much more complicated than had been generally supjiosed; and 

 finally, W. Dumas and Serret gave the complete theory of the experi- 

 ment. {J. Phys., March, 1885, II, iv, 147.) 



In constructing the reversible pendulum of Bohnenberger, Weber has 

 proposed to place the knife edges in such a way that any given varia- 

 tion of their distance may have the least possible influence upon the 

 duration of oscillation. Witli a cylindrical rod he finds that this con- 

 dition is realized when t= /rJ^_Z^/* and when the knife edges are 



/3-02045 

 V g 



placed symmetrically at a distance from the center x = 0'37835 a; a rei)- 

 resenting the moment of inertia of the pendulum around its center of 

 gravity. The value of a may be calculated geometrically and the length 

 of the simple synchronous pendulum I in the formula i=3-02045 a be 

 deduced from a determination of the time t, without having any meas- 

 urements of length to make other than those of the geometric dimen- 

 sions of the rod. ( Wied. Ann., xxii, 439; J. Phys., November, 1885, II, 

 IV, 510.) 



Oppolzer has obtained, by means of a Eepsold reversion pendulum, 

 the provisional value 0'993825 meter for the length of a seconds pendu- 

 lum in Vienna, lat. 48° 13' 57", altitude 236 meters. {Ber. Ale. Wien., 

 1884, p. 2; J. Phys., April, 1885, II, IV, 184). 



Sakai and Yamaguchi have determined the gravitation constant in 

 c. Or. s. units at Kagoshima and at Naha, in the Loo Choo Islands, using 

 the method employed b^^ Mendenhall iu Tokio. The value at Kagoshi- 

 ma was 979-561 ± 0-0057, and at Naha 979-165 ± 0-0055. {Am. J, Sci., 

 May, 1885, III, xxix, 404.) 



Bartoli has speculated on the mean density of a body containing all 

 the known elements in a solid state, either uncombined, or, if partly 

 combined, each retaining the density belonging to it in the solid state. 

 He makes three suppositions : (1) The masses of all the substances 

 equal ; (2) the masses such that the corresponding volumes shall be 

 equal, and (3) the masses in the ratio of the atomic weights. In this 

 way he arrives at the mean densities 2-698, 7-027, and 5-776, this last 



