or RENNET, the acid juice found in the stomachs of calves that have fed on nothing but milk, and are killed before the digestion is perfect. It curdles milk.

RUPERT'S DROPS, a sort of glais-drops with long and slender tails, which burst to pieces on the breaking off those tails in any part, said to have been invented by prince Rupert, and therefore called after his name. This surprising phenomenon is supposed to rise from hence, that while the glass is in fusion, or in a melted state, the particles of it are in a state of repulsion; but being dropped into cold water, it so condenses the particles in the external parts of their superficies, that they are easily re- duced within the power of each other's attraction, and by that means they form a sort of hard case, which keeps confined the beforementioned particles in their repulsive state; but when this outer-case is broke, by breaking off the tail of the drop, the said confined particles have then a liberty to exert their force, which they do by bursting the body of the drop, and reducing it to a very peculiar form of powder.