pastoral charge in Toledo, eighteen years ago. Though a Presbyterian, and loyal to the doctrines and polity of that church, he is remarkably free from sectarian exclusiveness, and all evangelical congregations seek and obtain his ministerial services.

Within the last year he has given more than twenty addresses at college commencements, and before literary and educational associations; while he has been obliged to decline numerous applications for like labors.

The weight of over fifty years and the work of a life of very great activity, rest lightly upon him. He is possessed of robust health, and is as marked for energy and vivacity as he was twenty years ago. But few men who have accomplished so much labor, seem still so able to repeat their life-work.

DOES THE EARTH REVOLVE?

BY T. C. MENDENHALL.

At what precise period in the history of the world, the motion of the carth on its axis was first suggested, is, perhaps, not positively known. From almost his own time to the present, lively disputes have been maintained as to whether Plato believed in its motion. We know from Archimedes that the doctrine was held by a contemporary of his, and there seems no question about its being advocated by some of the early Greek philosophers.

Its revival is evidently due to Copernicus. When this great astronomer gave us the heliocentric system which involves the diurnal rotation of the earth, it seems to have been so well done, and indeed so quietly done, that it received little or no opposition, and attracted but a small part of that attention which was justly its due. It appears rather to have slumbered for near a hundred years, when it was brought prominently before the people by a most enthusiastic champion in the person of that eminent philosopher, Galileo. Of this remarkable man we find most conflicting opinions entertained. The principal events in his life are familiar to all. Was or was not Galileo a martyr? On the one hand he is represented as an artless, impatient philosopher, too eager in urging his favorite theories, and guilty of duplicity both in his writings, as in the preface to his celebrated dialogue,

and in his actions, as when, after having renounced his faith upon his bended knees, he rises with his immortal" E pur si muove." It is claimed that he was punished for his intermeddling with the Holy Scriptures-not because he was a good astronomer, but because he was a bad theologian; that his imprisonment was only nominal; that he was always treated with great respect and indulgence, and never subjected to bodily torture.

Again we see him, armed with his newly invented telescope, an humble but an earnest and vigorous lover of truth. We are told that he expressly declares that he does not persist in attempting to reconcile the Bible with the theory of Copernicus; that he considers the Scriptures especially intended to teach men how to go to heaven-not how heaven goes; that he suffers greatly from the persecution of his enemies, and that, when he was summoned to appear before the inquisition, "neither the infirmity of his health nor the pain he suffered from a rheumatic complaint which afflicted him, could procure exemption from that sorrowful journey." Before this body he defended himself by claiming that if the Bible could be properly interpreted, it would in no manner whatever conflict with the truths of science; but the declaration was made that "the proposition that the sun is in the centre of the world and immovable from its place, is absurd, philosophically false, and formally heretical, because it is expressly contrary to the holy scripture," and he was condemned to "abjure, curse, and detest the error and heresy of the motion of the earth," to suffer imprisonment for an indefinite period, and to recite once a week for three years the seven penitential psalms. The whole sentence of the Inquisition on Galileo is a curiosity, and has been truly characterized as "one of the most remarkable records of intolerant ignorance and bigoted folly to be found in the history of science."

Be the case as it may, we certainly owe to him a debt of gratitude for reëstablishing the true theory of the earth's position in the universe, and so agitating men's minds upon the subject that it became fixed for all time to come. It is a curious fact that Francis Bacon, with whom Galileo divides the honors of the inductive philosophy, is supposed to have doubted the motion of the earth on its axis. Even after the time of Newton, some were of a like opinion. An edition of his Principia was published, in the preface to which the publishers were careful to say that the author has proceeded upon the supposition of the earth's diurnal motion.

Within the last hundred years the motion of the earth has been universally admitted as a necessary astronomical assumption. I believe Prof. Airy remarked that until the discovery of the aberration of light, there existed no positive proof of the motion of the earth in its orbit, and it has also been stated that there was no positive proof of its diurnal motion previous to the year 1851, at which time M. Foucault devised the very ingenious experiment which has since borne his name. Having a slender steel rod fixed in the arbor of a lathe it was accidentally put in vibration, and the arbor being slowly turned round he noticed that the rod continued to vibrate in the same plane. This would have been a little thing to most men, but such things become great in the hands and brains of genius. His first application of this principle to the proof of the rotation of the earth was made by hanging a pendulum only six feet in length in a cellar, and starting its vibrations over a line drawn on the floor, from which it was found in a short time to deviate on account, as he correctly inferred, of the motion of the earth. To make the deviation clearly visible to a number of persons, a pendulum of considerable length is required. After Foucault had communicated his discovery to the French Academy, a trial was made with great success in the Pantheon at Paris, with a pendulum 220 feet in length. It was soon repeated in various other places in Europe and in this country, especially at Bunker Hill Monument, in which was suspended a pendulum 210 feet long.

Some time ago it appeared to me that the rotunda of our own State House offered a most excellent point of suspension for a pendulum for the repetition of this experiment. A pendulum 120 feet in length could be made to swing there, and as far as I can ascertain but two longer have ever been used. I accordingly obtained permission, and made preparation for the experiment which was exhibited a short time since, and with such satisfactory results that I beg to offer an account of it, in the hope that my example may be followed under, perhaps, less favorable circumstances. As some of my readers may desire to repeat the Foucault experiment, I hope I shall be pardoned for explaining with considerable minuteness my method of performing it. I have often, in endeavoring to reproduce anything of this kind, felt the need of a few directions or suggestions in regard to little things, which, as every experimenter well knows, contribute so much to success or failure.

I procured a sold iron ball, weighing about 23 pounds. After

it was carefully centered and turned off by a machinist, a hole one-quarter of an inch in diameter and one inch in depth wast drilled on one side, and diametrically opposite another half an inch in diameter and three-fourths of an inch deep. In the latter a thread was cut so a screw could be put in it, in the exact centre of which was drilled a fine hole just large enough for the wire which is to be put through, and secured by twisting or otherwise. After this the ball may be easily screwed on. In the small hole opposite, a wooden pointer five inches in length was fastened, to show more clearly the path of the pendulum. At the point of suspension, the wire may be simply passed through a small hole in a plate and soldered fast. After which the plate is to be securely fastened to the ceiling of the room in which the experiment is performed.

My arrangement consisted of a piece of iron shaped like a stirrup, about two inches long and one and a half inches wide. The wire was passed through a hole, in which it fitted nicely, in the convex part, so that the stirrup hung in an inverted position. From the centre of the upper or flat part, there protruded downward steel point half an inch long. This was the point of suspension proper, and was made to rest on a little hollow spot on a steel hook, which was firmly screwed into an iron bar crossing the small open space in the top of the rotunda. The pendulum can best be suspended by wire, and the lightest which will certainly and securely sustain the weight of the ball, is the best. It is well to put up the apparatus, and let the pendulum hang for 24 hours before performing the experiment.

The hourly deviation is obtained by multiplying 15° by the sine of the latitude. This amounted in Columbus to about 9° 40'; and after drawing upon the floor of the rotunda a north and south line, I had others drawn making this angle, and all having a common point immediately below the centre of the pendulum ball. Every thing being ready, the ball was drawn off towards the south, about 10 feet from its point of equilibrium, so as to give it an amplitude of about 20 feet. A loop of thread was thrown round it, and the end was fastened to a nail in the floor, so that the ball was held in that position when it was allowed to remain for a half an hour in order to come perfectly to rest that it might be free from all wabbling motions. At the end of this time the thread was burned off, and the ball started on its motion with a beautiful regularity and steadiness, moving almost exactly over the central point of the plane, and following with consider

able accuracy the north and south line. It made almost exactly ten vibrations in a second, which, as the reader can readily see, corresponds closely with the results of calculation.

As the ball made its slow and solemn beats from north to south and back again, across the marble floor of the capitol, it was eagerly watched by many bystanders who had assembled, curious to see the earth move. Scarcely a half dozen vibrations had been made before we began to perceive the deviation, and to see that the earth had turned underneath the pendulum, which was now going a little to the east at the north end and to the west at the south end. In one hour it was vibrating almost exactly over the first line of hourly deviation, distant 9° 40' from the starting line-thus agreeing with the result of calculation more nearly than was anticipated. It was allowed to swing for three or four hours, and the agreement between the theoretical and experimental results was most satisfactory.

In performing this experiment it will be noticed that the ball can in no case move directly over the central point. The ellipticity of its motion is a necessary result of the motion of the earth, but this, however, is quite small; the greater part of that generally observed is due to the imperfection of the experiment.

The theory of this experiment is generally understood. The simplest illustration which I have been able to devise, is to take a globe, and selecting any parallel of latitude-say the 40th— draw first a short meridian line crossing it, which shall represent the line over which the pendulum first swings. Then, with a short slip of paper or card-board, with its edges parallel, draw a line to the right and parallel to this; slide the slip along until the left edge shall coincide with the last line, and then draw another, and so on. These lines being parallel to each other will represent the positions of the plane of vibration at the different points, and will rapidly deviate from the meridian line. If carried entirely around the globe, the number of hours necessary to complete a revolution is very approximately ascertained.

It is hardly necessary to state that many modifications of this experiment can be contrived, and that M. Foucault has employed the gyroscope for the same purpose, which illustrates the same principle of persistence in the plane of vibration.

I have two or three elegant demonstrations of the law that the deviation of the plane of vibration varies as the sine of the latitude; but I would not deprive those whose tastes run in that direction, of the pleasure of inventing them.