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Let AB and CD be two rods of any solid of the same species, and of a simple or uniform texture. Let these two rods be exactly of the same length; let them be connected at the top with a rod BC, which is perfectly inflexible, let the angles ABC, and DCB, be both right angles, so that AB and DC shall be parallel to each other, and in the same plane ; let the rod AB be fixed at the point A, and perpendicular to the horizon: then the rod CD shall likewise be perpendicular to it, excepting for the curvature of the earth between B and C, which in a foot or two may be considered as nothing: let the rod CD be loose at the end D, so as to be capable of rising up or falling down; in this case, if heat be applied equally to both rods, so as to expand them both, and lengthen them, the rod AB will raise up the rod BC, and lift up the rod DC; but the rod DC being equally lengthened by heat with the rod BA, the point D will be brought downwards by the lengthening of the rod DC, as much as the point C is raised by the lengthening of the rod AB by the heat. In consequence, the rod DC will have its end D in a line exactly parallel to the horizon, and cutting the end of the rod AB at A, as it did before the heat was applied ; and the same thing will be true if the rods AB, DC, be shortened by exposure to cold ; so that in all cases of heat or cold the end of the rod CD at D, and the end of the rod BA at A, shall be in a line parallel to the horizon. Take a point E near any part of the rod CD, and let that point E be connected with the point A, where the end A of the rod AB is fixed, and let the matter which unites them be perfectly inflexible, and incapable of being altered by heat; then, I say, that the part of the rod CD, intercepted at the point E, and forming ED, will always be of the same length whether the temperature of heat is greater or less. For supposing a point F be taken near the rod AB, and of the same perpendicular height with E, so that a line drawn from E to F shall be parallel to the horizon ; if the part of the rod AB, opposite to F, should rise up in consequence of being expanded by heat above F, it will carry up the point of the rod DC, which was opposite to E, to an equal height with itself, and therefore would cut off from the length of that part of the rod which was formerly opposite to E, a length equal to that which was added to what was formerly ED, by the heat. Therefore the point opposite to E, in the rod DC, will form ED, which will always continue of the same length, if the heat be increased ; and by similar reasoning, it will likewise continue of the same length if the part of the rod AB AF is shortened by cold; therefore the part of the rod DC cut off by the point E, so as to form ED, will always be of an equal length, and the point D will always be of an equal height.

II. Account of a new pendulum. By George Fordyce, M.D. F. R. S.; being the Bakerian Lecture