ADDRESS OF PROFESSOR LOVERING. 617 
by the isochronous vibrations of the chandelier, which during the 
long centuries has never been absolutely at rest. When it is said 
that the pendulum has no rival as a standard of length except the 
metre, that it furnishes an exact measure of time, and that time 
isan indispensable element in the study of all motion, and also 
the most available means of obtaining longitude on the earth and 
tight ascension in the heavens, a strong case has been made out 
for the practical and scientific usefulness of Galileo’s discovery. 
During the long years of doubt in regard to the true figure of the 
earth, the pendulum maintained the cause of Newton in opposition 
to the erroneous reports of the geodesists, until Maupertuis, by a 
new measurement, flattened, as has been pithily said, the earth and 
the Cassinis at the same time. The shape, rotation, and density of 
the earth ; the diminution of terrestrial gravity with an increase of 
distance from the centre; the local attractions of mountains, and 
Secrets hidden below the surface of the planet, have been dis- 
Covered or verified by the declarations of the pendulum: which, 
Whether in motion or at rest, has never tired of serving science. 
And, in a wider sense, the pendulum has done for the electric and 
Magnetic forces what, in its restricted meaning, it did for gravity. 
That which Borda failed of accomplishing in the measurement of 
ares the pendulum realizes in its measurement of time: it multi- 
Plies its observations, eliminates its own errors, strikes its own 
average, and presents to science the perfect result. In 1851, a 
crowd of spectators was assembled in the Pantheon of Paris to 
Withess the first performance by the pendulum of the new part 
Prepared for it by Foucault: in which, obedient to its own inertia, 
are indifferent to the earth’s rotation, it preserves the parallelism 
of its motion: an experiment startling though not wholly unantici- 
Pated, and which has made the circuit of the earth. The new con- 
trivance of Zöllner promises to indicate changes in the direction of 
a force as accurately as the common pendulum measures intensity. 
Let us now consider what the physicists of our own day, and 
immediate predecessors, have added to their rich inheritance 
of instrumental means, remembering all the time that, however 
ive from their novelty these additions may be, and how- 
ever manifold their applications, they have only supplemented the 
“Xperimental methods which have been described without sup- 
Planting them. For the most part, the later devices would be 
Useless without the coöperation of the earlier ones. 
