OF THE MOTION, REFRACTION,

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ing the velocity of light. The minutest: parti-^ cles which are thrown off from the body of thefun, move through a space of ninety-five mil-lions of miles in eight minutes ; which is abouta million of times swifter than the motion of acannon-ball, when it is first projected from themouth of the piece; a rapidity too great for the;,. t i imagination to .'follow, or the mind to compre-hend. And yet, prodigious as such a motionappears, there may be stars, whose light has notreached us fince the creation of the world. Thitis the universe of the poet;

Without bound,

Without dimension, where length, breadth, and height,And time and place are lost.”

The quantity of light and heat which theplanets receive from the fun, decreases in pro-portion as the squares of their distances increase;and when a ray of light passes out of one me-dium into another, it is refracted or turned outof its first course, according as it falls more orless obliquely on the refracting surface whichdivides the two mediums. The first of thesepropositions will appear evident, from the con-sideration of a cone of rays, flowing from anyluminous point, the circular sections of whichwill be always proportional to the squares oftheir distances from the vertex ; and the lattermay be exemplified as follows: put a shilling

into