My first idea on this subject, is the following: If we had on ship-board, a simple pendulum of several thousand feet high, it appears certain that the oscillations of the ship would be begun and ended, before any single vibration could have been given to such a length of pendulum—which therefore, would scarcely vibrate at all: and if the natural time of this compound pendulum (for we are not confined to these small dimensions) were made to be much longer than those of the ship on it’s meta-centre, this pendulum would scarcely vibrate at all: because it’s several tendencies to take motion from the ship, would extinguish each other before they had had time to produce any common effect.
Further, this result would probably be assisted by another property belonging to this mechanism: see [fig. 4]. This diagonal suspension, as repeated at a b c d, [fig. 4], is of such a nature, that when it’s centres a b, are placed in any oblique position e f, (say by the rolling of a ship) the suspended bar c d, immediately takes a position of opposite obliquity g h, pointing upward towards i, just as much as the line e b points downward; while the middle line k l remains level—whether caused by the slides k l, or the single slide m.
I dare not assert any thing respecting the form this principle should assume, in order to produce the most useful effects; but it appears that the principal weight of the apparatus should be placed in the centre of gravity of the under bar c d. It would occur, of course, to every mechanician applying this System to real use, that in this [fig. 4], we have only provided for one motion of the ship, the rolling motion: and that, in consequence, this System should be suspended in another similar one, acting longitudinally, so as to provide for the pitching motions of the vessel. In a word, I confess, with regret, that I leave much to do, by way of bringing this idea to maturity—it being at this late hour, more than doubtful, whether I shall myself ever be able to resume the subject at sea, where alone it can be duly tried.
OF
A SECOND ESSAY,
To procure a Marine Level.
This would seem to be a simpler process than the former: but how far it may go beyond it in effect, I cannot say—having never had it in my power to try either of these ideas on ship-board. I therefore merely present them to my readers, as themes for future thought and experiment.