GRAVITY (in Physics.) The natural tendency or inclination of bodies towards a centre. Terrestrial gravity, is that force by which all bodies are continually urged towards the centre of the earth. It is in consequence of this force that bodies are accelerated in this fall, and when at rest that they press the body, or that part of the body by which they are supported. As to the cause of gravity, or its nature, nothing whatever is known, and it would be useless and unprofitable tp occupy any part of this article in detailing the several vague hypotheses that have been advanced to account for this most important law of nature. All that can be said is, that it appears to be an essential property of matter, or, at least, of all matter that has hitherto become the object of human investigation, though it is by no means certain that matter may not exist which is not subject to its influence. Specific gravity, is
the relative gravity of any body or substance, considered with regard to some other body which is assumed as a standard of comparison, and this standard by universal consent and practice, is rain water, on account of its being less subject to variation in different circum stances of time, place, ctc. than any other body, whether solid or fluid. And, by a very fortunate coincidence, at least to English phi losophers, it happens that a cubic foot of rain water weighs 1000 ounces avoirdupois ; and consequently, assuming this as the specific gravity of rain water, and comparing all other bodies with this, the same numbers that ex press the specific gravity of bodies, will at the same time denote the weight of a cubic foot of each in avoirdupois ounces, which is a great convenience in numerical computations.