The opinion of the court was delivered by

— It was said in Riddle v. Dixon, 2 Barr 364, that an error in hydrostatics is not a subject of legal adjudication; but it becomes an error in law, when the court gives it a direction that may lead the jury to error of fact. There was a conflict of testimony in this case, and witnesses, who swore that the surface of the pool at the dam was no higher than the permanent watermarks on the old forebay and the shores, were confronted with witnesses who swore that it was raised at the upper end of the pool, for that more of the plaintiff’s land had been submerged since the erection of the new dam than was submerged before it. Both sets could not be right; for it is an eternal principle, that water finds its level; yet the court pointed out a middle ground to reconcile them, by directing, that if by changes in the bed of the stream above the dam, the water was thrown further back by reason of the obstruction raised by the dam, than it had been for twenty-one years, the defendant would be liable for the additional injury, though the height of the dam may not have been increased. But such an effect, from such a cause, was impossible. No deposit in the pool or excavation in the *269channel above it, could alter the pitch of the surface; and, as was said in McCalmont v. Whitaker, 3 Rawle 84, it is the relative height of the surface which determines the quantity of the water power. No matter how much the bottom of the stream may have been washed away, the effect would be to deepen the water in it, not to overflow its banks; nor could any sand-bar be occasioned by the dam which would produce the supposed effect. The direction, consequently, tended to withdraw the attention of the jury from the conflict of testimony, which it was their business to dispose of.

Judgment reversed and a venire de novo awarded.