158 ANNUAL OP SCIENTIFIC DISCOVERY. 



hypothesis, but seem to show that the latitude of a place may be found 

 by this means with a considerable degree of accuracy. 



A new contrivance for exhibiting the rotation of the earth is reported 

 to have been devised by Prof. Strong, of Rutger's College, N. Y. He 

 has constructed a wooden wheel, six feet in diameter, but very slight 

 indeed its weight being only two pounds. This wheel is supported 

 horizontally, the hub resting on a steel needle, in the same manner 

 that a compass is supported. This needle fits into a glass socket. 

 This apparatus being placed in a room free from currents of air and all 

 disturbance, the motion of the earth around the wheel is perceptible ; 

 the wheel apparently performing the revolution in the proper number 

 of hours. By this wheel it is said that the latitude can at all times be 

 correctly ascertained. The experiment is not confined to a wheel of 

 such large dimensions, but may be realized with smaller ones. 



NEW METHOD OF DEMONSTRATING THE ROTATION OF THE EARTH. 



THE recent experiment of M. Foucault, giving direct proof of the 

 earth's rotation, having excited so much attention, it seems remarkable 

 that an equally striking one, devised and tried by M. J. Guyot, in 

 1836, should have been passed over or forgotten. That gentleman 

 observed, that as a falling body deviates to the east, a long plumb-line 

 ought to do the same. This experiment he performed in the dome of 

 the Pantheon, at Paris, with a plumb-line, about 172 feet long, and 

 determined the deviation to be four and a third millim. in 57 metres. 

 His mode of experimenting was by small balls, one at the point of sus- 

 pension, the other at the weight, whose images, strongly illuminated 

 and reflected in a basin of mercury placed below, were viewed from 

 above, and found to coincide when the eye was laterally distant 

 four and a third millim. from the upper ball. The experiment might 

 probably be simplified without the trouble of illumination, by making 

 the suspension from a line passed across a small circular aperture in a 

 flat roof, the light coming through which would probably give a suffi- 

 ciently light image in the mercury below. The effect is also stated 

 to be sufficiently perceptible with much less length than that above 

 stated. 



DEMONSTRATION OF THE ROTATION OF THE EARTH BY MEANS OF TWO 



PENDULUMS. 



AT the Institution of Civil Engineers, London, the following com- 

 munication was read by Mr. Cox : 



" The demonstration of the rotation of the earth was usually made 

 to depend on phenomena presented by the appearance of the heavens. 

 Two mechanical experiments had, however, long been known, which 

 demonstrated the fact that the earth revolved : the one, the retarda- 

 tion of the pendulum by centrifugal force, a question discussed by 

 Newton, Huygens, and others ; the other, which was suggested by 

 Newton, consisted in dropping, from a great height, a ball, which, by 



