virtuoso. Fossils, in truth, are to the geologist, what medals are to the antiquary, preserving a record of events which must otherwise have perished in the stream of time."

Mr. and Mrs. Seymour and the vicar by this time arrived at the Wernerian Temple, where having discussed several points connected with its objects, Mr. Twaddleton gave an account of Major Snapwell, whose history created considerable interest, and determined Mr. Seymour to call at Ivy Cottage, and invite its inmate to the lodge.

THE SUBJECT OF ROTATORY MOTION CONTINUED.A BALL, BY HAVING A PECULIAR SPINNING MOTION IMPARTED TO IT, MAY BE MADE TO STOP SHORT, OR ΤΟ PROCEED IN A RETROGRADE DIRECTION, THOUGH IT MEETS WITH NO APPARENT OBSTACLE. THE RECTILINEAR PATH OF A SPHERICAL BODY INFLUENCED BY ITS RO

BALL.

THE JOINT FORCES WHICH ENABLE THE BALANCER TO THROW UP AND CATCH HIS BALLS ON THE FULL GALLOP. THE HOOP. THE CENTRE OF PERCUSSION. THE CENTRES OF MAGNITUDE AND GRAVITY. THE LINE OF DIRECTION. THE STABILITY OF BODIES, AND UPON WHAT IT DEPENDS. 1 METHOD OF FINDING THE CENTRE OF GRAVITY OF A BODY. THE ART OF THE BALANCER EXPLAINED AND EXEMPLIFIED.

"Toм, do you remember that I told you a few days ago," said Mr. Seymour, "that, by giving a revolving body a peculiar spinning motion, certain effects were produced, which I should, on some future occasion, take into consideration?"

"To be sure I do," replied Tom. "Well then, attend to me."

Mr. Seymour took a marble, and, placing it on the ground, gave it an impulse forward by pressing his forefinger upon it: the marble darted forward a few paces, after which it rolled back again.

"That is most extraordinary!" cried Tom ; "the marble came back to your hand, as it were, of its own accord, and without having met with any obstacle."

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"And you, no doubt," said Mr. Seymour, regard it as contrary to the well known law, that a body once put in motion, in any direction, will continue to move in that direction until some foreign cause oppose it."

"It really would appear so."

"It is, however, far otherwise; the force

which I imparted to the marble communicated to it two kinds of motion; the one projecting it forward, the other producing a rotatory motion round its axis, in a direction opposite to that of its rectilinear course; and the consequence was simply this, that when the former motion, on account of the friction of the marble on the ground, was destroyed, the rotatory motion continued, and by thus establishing an action in an opposite direction, caused the marble to retrograde. If, however, you will fetch your hoop, I will demonstrate the fact on a larger scale."

Tom accordingly produced the hoop; and Mr. Seymour projected it forward, giving to it, at the same instant, a spinning motion in an opposite direction. The hoop proceeded forward to a certain distance, when it stopped, and then ran back to the hand.

"Let me beg you," said Mr. Seymour, "to treasure this fact in your memory; you perceive by it how greatly the progressive direction of a body may be influenced by a rotatory motion around its axis; and, indeed, the theory of the rifle gun (14) is easily deduced from it. It will also explain the effect which a rotatory motion

produces in steadying or disturbing the direction of a projectile. It is for this reason that the balancer constantly whirls round his balls or oranges, as he throws them into the air, with the intention of catching them again.” "But I do not understand," said Tom, "how such a spinning motion can produce the desired effect."

"Have I not frequently warned you against idleness; and do you remember for what reason ?"

"You have always said, that an idle boy is sure to get into mischief."

"True; there is an activity in the mind which must be satisfied, and if worthy occupations are not presented to it, it will naturally employ itself by others less salutary. So is it with a ball or orange, it will have a tendency towards rotatory motion, and if left to itself, will assume an untoward axis; to prevent this you give it an axis upon which it may spin with the greatest advantage.”

"I do not exactly understand what is meant by an untoward axis," said Tom.

"Suppose a projectile should have a rotatory motion about an axis, which does not coincide