336 PHYSICS. 



tation, apparently iudepeudeut of any external meteorological condi- 

 tion. The apparatus, while quite insensible to local tremors, was ex- 

 traordinarily sensitive to steady forces. A person standing in the room 

 IG feet distant, and then 17 feet, the difference in the yielding of the 

 floor and the consequent tilting toward the point of pressure of the 

 stone basement, was plainly apparent. An alteration of the plumb- 

 line by 0.01 second was distinctly measurable. The authors draw from 

 these results some important practical conclusions. They suggest 

 greater precautious to protect the piers of transit instruments from 

 changes of temperature, and to provide for the drainage of the sod 

 round their bases. The effect of the weight of the observer's body should 

 be guarded against. {Nature, November 3, 1881, xxv, 20,) 



Eespighi has finished his experiments to determine the intensity of 

 gravity at the observatory of Campidoglio. He used a pendulum com- 

 posed of a ball of lead 9i kilograms in weight, supported by a steel 

 wire 0.6 millimeter in diameter. Five different lengths were used, vary- 

 ing from 7.9 to 5.16 meters. These pendulums proved independeitt of 

 the earth's rotation, and showed Foucault's phenomenon perfectly. At 

 each oscillation the point attached to the pendulum dipped in mercury, 

 thus making an electric contact which was recorded on a chronograph. 

 The data obtained have not yet been fully reduced. {Nature, May 19, 

 1881, xxiv, 67.) 



Mendenhall has determined the value of gravity upon the summit of 

 Fujiyama in Japan, using a Kater's pendulum, from which one of the 

 knife-edges, the "tail-pieces," and allot the unnecessary parts were re- 

 moved, and an adjustable slide-piece fixed on the piece projecting above 

 the knife-edge. A Negus break-circuit chronometer, a chronograph, 

 and a i)ortable transit instrument were also used. After the necessary 

 corrections, the value of gravity on the summit of the mountain w^as found 

 to be 9.7886. In Tokio it had been previously determined as 9.7984. 

 From these values, taken in connection with certain data concerning 

 the mountain, Mendenhall has sought to calculate the mean density of 

 the earth. The result obtained, assuming the density of the mountain 

 to be 2.12, gives 5.77 for the earth's density. As this is slightly above 

 Baily's value, 5.67, the author reverses his calculation, and assuming 

 this value, calculates the density of the mountain, and finds it to be 

 onl}' 2.08; thus suggesting deficiency in its attraction. {Am. J. Sci., 

 February, 1881, xxi, 99.) 



MECHANICS. 



1. Of solids. 



Stevenson has presented to the Eoyal Society a paper on the influ- 

 ence of stress and strain on the action of physical forces. He finds 

 that (1) after a wire has suffered permanent extension the temi)orary 

 elongation produced by a load diminishes as the interval between the 



