"At the centre of the dome of the Panthéon a fine wire is attached, from which a sphere of metal, four or five inches in diameter, is suspended so as to hang near the floor of the building. This apparatus is put in vibration after the manner of a pendulum. Under and concentrical with it is placed a circular table, some twenty feet in diameter, the circumference of which is divided into degrees, minutes, &c., and the divisions numbered. Now, supposing the earth to have the diurnal motion imputed to it, and which explains the phenomena of day and night, the plane in which this pendulum vibrates will not be affected by this motion, but the table, over which the pendulum is suspended, will continually change its position, in virtue of the diurnal motion, so as to make a complete revolution round its centre. Since, then, the table thus revolves, and the pendulum which vibrates over it does not revolve, the consequence is, that a line traced upon the table by a point projecting from the bottom of the ball will change its direction relatively to the table from minute to minute and from hour to hour, so that if such point were a pencil, and that paper were spread upon the table, the course formed by this pencil would form a system of lines radiating from the centre of the table. The practised eye of a correct observer, especially if aided by a proper optical instrument, may actually see the motion which the table has in common with the earth, under the pendulum between two successive vibrations. It is, in fact, apparent that the ball, or rather the point attached to the bottom of the ball, does not return precisely to the same point of the circumference of the table after two successive vibrations. Thus is rendered visible the motion which the table has in common with the earth."
Crowds are said to flock daily to the Panthéon to witness this interesting experiment. It has been successfully repeated by Professor Ansted at the Russell Institution, in London, in a manner similar to the experiment at the Panthéon at Paris. The wire, which suspended a weight of twenty-eight pounds, was of the size of the middle C-string of a piano. It was thirty feet long, and vibrated over a graduated table fixed to the floor. The rotation of the table, implying that of the earth on which it rested, was visible in about five minutes, and the wonderful spectacle was presented of the rotation of the room round the pendulum. The experiment excited the astonishment of every beholder, and many eminent scientific gentlemen who were present expressed their great delight in witnessing a phenomenon which they considered the most satisfactory they had witnessed in the whole course of their lives.