582 SCIENTIFIC i7i:roKM) von issr>. 



value, as he points out, coming very near that got by Cavendish for the 

 mean density of the earth, which was 5'67. {Nature, October, 1885, 

 XXXII, 635.) 



Wilsiug has revived the use of the pendulum for determining the 

 earth's mean density, and has shown that the necessary sensitiveness 

 may be secured by adjusting so that the center of gravity comes close 

 under the axis of oscillation. In his experimental apparatus fixed leaden 

 balls, each weighing 300 grams, were placed at the ends of a prismatic 

 rod of thin sheet iron, the steel knife edge being in the middle of the 

 rod and resting on agate i)laues. After adjustment to equilibrium, the 

 attracting masses were brought near the leaden spheres and the deflection 

 read by means of a mirror and scale. From the value thus obtained the 

 ratio of the deflecting attraction to the constant of gravitation can be 

 deduced. By reversing the direction of the deflecting force the total 

 deviation is doubled. An improved apparatus, in i)rocess of construc- 

 tion, will, it is expected, give accurate results. {Ber. A]c. Berl., January, 

 1885; FJiil. ilfa^., March, 1885, Y, xix, 210; Avi. J. Sci., May, 1885, III, 

 XXIX, 402.) 



Konig and Kicharz have suggested an improvement of Von Jolly's 

 method for determining the earth's mean density. A cubical block of 

 lead, about 2 meters in the edge and weighing 100,000 kilograms, is so 

 placed that the center of its upper horizontal surface is exactly beneath 

 the middle knife edges of an extremely delicate balance. Beneaih the 

 center of each scale-pan the block is bored vertically through, and two 

 other scale-pans are suspended below the block by means of rods pass- 

 ing through these openings. A weight iu one of the ujiper pans is bal- 

 anced by weights in the opposite lower pan. The former is acted on by 

 the earth's attraction plus that of the block, the latter by the difference 

 of the two. Hence, the weights in the lower pan are greater than those 

 in the upper by twice the attraction of the block. A second weighing 

 is then made, the other two pans being now used. The difference of 

 the two weighings gives four times the attraction of the block. {Ber. 

 Ale. Berl, December, 1884; Phil Mag., February, 1885, V, xix, 148; 

 Nature, January, March, 1885, xxxi, 200, 408, 484.) 



MECHANICS. 



1. Of Solids. 



In a paper read at the Aberdeen meeting of the British Association, 

 Osborne Reynolds discussed a new and very fundamental property of 

 granular masses composed of rigid particles in contact, which property 

 he calls Dllatancy. It is exhibited in any arrangement of particles where 

 change of bulk is dependent upon change of shape. In fluids change 

 of shape and volume are independent, but in solids they are sometimes 

 not separable. With granular masses change of shape always produces 

 change of volume, and if change of volume is prevented any change of 



