PHYSICAL AND MATHEMATICAL SCIENCES. 203

what he calls the “ prerogativa instantiarum,” or thecomparative value of facts, as means of discovery ofcauses. He enumerates not less than twenty-sevensuch points of distinction, entering at length into thepeculiarities of each. We will exemplify their natureby noticing a few of the most remarkable.

The “ instantiae solitaries” are examples either ofthe same quality existing in two bodies which havenothing else in common, or of a quality in which twobodies differ, when in all others they are alike. Ineither case the hypotheses as to the form or cause arelimited : in the first case they can involve none of thosethings in which the bodies differ ; in the second, noneof those in which they agree.

Bacon gives an exemplification of the first of thesecases, which is somewhat remarkable. Of the cause,or form of colour, he says, instantice solitaries occur incrystals, prisms of glass, and drops of dew, whichoccasionally exhibit colour, and yet have nothing incommon with the stones, flowers, and metals, whichpossess colour permanently, except the colour itself.Hence he concludes that colour is nothing else thana modification of the rays of light, produced, in thefirst case, by the different degrees of incidence; and inthe second, by the texture or constitution of the sur-faces of bodies: a remarkable anticipation of whatNewton was soon to establish experimentally.

The instantice radii are cases measured by lines andangles; the instantice curriculi by time.

Under the former head Bacon makes some remarks,which are singular for the extent of view they discover,even in the infancy of hysical science. He mentionsthe forces by which bodies act on one another at a dis-tance, and throws out some hints on the attractionwhich the heavenly bodies exert on one another. “ Itis to be enquired,” says he, “ whether there be anymagnetic force which acts mutually between the globeand heavy bodies, or between the moon and the sea, orbetween the starry heaven and the planets, by which