“I have here,” said Mr. Seymour, as he opened a large wooden box, “a collection of figures, which will always raise themselves upright, and preserve the erect position; or regain it, whenever it may have been disturbed.”
He then arranged these figures in battalion on the table, and striking them flat by drawing a rod over them, they immediately started up again, as soon as it was removed. “These figures,” continued he, “were bought at Paris some years ago, under the title of Prussians.”
“I declare,” exclaimed the vicar, “they remind me of the rebellious spirits whom Milton represents as saying that ascent is their natural, and descent their unnatural, motion.”[[10]]
“I have seen skreens similarly constructed,” said Mrs. Seymour, “which always rose up, of themselves, upon the removal of the force that had pressed them down.”
“I will explain their principle,” said Mr. Seymour.
“Suppose we first examine the construction of the figure,” observed the vicar. “Bless me! why it is like Philotus the poet, who was so thin and light, that lead was fastened to his shoes to prevent his being blown away.”
“The figure,” said Mr. Seymour, “is made of the pith of the elder-tree, which is extremely light, and is affixed to the half of a leaden bullet; on account, therefore, of the disproportion between the weight of the figure and that of its base, we may exclude the consideration of the former, and confine our attention to the latter. The centre of gravity of the hemispherical base is, of course, in its axis; and therefore tends to approach the horizontal plane as much as possible, and this can never be accomplished, until the axis becomes perpendicular to the horizon. Whenever the curved surface is in any other position, the centre of gravity is not in the lowest place to which it can descend, as may be seen by the diagram which I have just sketched. If the axis a b be removed to c d, it is evident that the centre of gravity will be raised, and that, if left alone, it would immediately descend again into its original position.”
“I understand it perfectly,” said Tom. “When the axis a b is perpendicular, the centre of gravity will be in its lowest point, or as near the earth as it can place itself; when, therefore, the figure is pressed down, the centre of gravity is raised, and, consequently, on the removal of that pressure, it will descend to its original position, and thus raise the figure.”