380 POPULAR SCIENCE REVIEW. 
kilos, from a wire 67 metres long, beneath the dome of the Pantheon, in 
Paris. A posthumous note in explanation of the observation is published in 
the recently collected works of the great physicist. He fully appreciated 
from the first that the rapidity of the deviation is equal to the Earth’s 
velocity multiplied into the sine of the latitude of the place of observation ; 
corresponding simply with sidereal time at the Pole, and being infinite at the 
Equator. The pendulum had a period of eight seconds for each vibration. 
It continued in motion with a single impulse for six hours, making a com- 
plete rotation in thirty-one hours, and a deviation of 1' 33" in each oscillation. 
By this noble experiment he substantiated an important physical fact, namely, 
the fixedness of the plane of oscillation, as a consequence of vis inertia in 
matter generally. This he afterwards demonstrated still more ingeniously 
by means of a delicately-suspended gyroscope. Another less known form of 
the experiment is also recorded in his works. A thin, long, elastic rod of 
steel is fixed to the mandril of an ordinary lathe, being free at the farther 
end. If this be pulled at the free end out of its position of rest, it vibrates 
in a series of fines, circles, and ellipses, following each other in regular succes- 
sion. The same phenomenon is seen in Wheatstone’s kaleidophone. When, 
however, a steady oscillation has been obtained, it is not interfered with in 
direction by causing the mandril and the attached rod to rotate rapidly about 
their axis ; the plane of oscillation continuing stable though the mass of the 
vibrating body is in motion. Even beyond this, the rotation protects the 
oscillatory plane against deformations due to unsymmetry of the rod, and 
renders it more stable than in a state of rest. Indeed, whatever form the 
vibratory curve may have taken up, whether linear, circular, or elliptical, 
this is preserved unchanged as long as the axial rotation is kept at a certain 
speed. 
ZOOLOGY. 
A Synthetic Starf.sk . — In the Popular Science Peview for April (p. 192), 
we called attention to an interesting form of starfish, apparently bridging 
over the gap between the Stellerida and the Ophiurida, which had been 
described by Mr. W. Percy Sladen. M. E. Perrier has lately described a 
still more remarkable type obtained during the dredging operations of 
Mr. Alexander Agassiz, in the deeper parts of the Gulf of Mexico. This 
starfish is very delicate in its structure ; it has a rounded disc distinctly 
separated from the arms, as in the Ophiurida, and the arms are elongated, 
flexible, and furnished with lateral rows of spines, thus increasing the 
general resemblance to the Brittle Stars. But there are twelve arms, whilst 
no known ophiurid has more than seven. The description of the disc is 
very curious, and nothing like it is known elsewhere among starfishes. It 
is flattened, very thin and quite destitute of any regular skeleton, the dorsal 
membrane being in fact literally a circular membrane stretched upon the 
ring formed by the basal ossicles of the arms ; it is membranous and trans- 
parent, and so close to the buccal membrane that the stomach has only a 
space about equal to the thickness of a sheet of paper in which to lodge. 
