. The Civil engineer and architect's journal, scientific and railway gazette. Architecture; Civil engineering; Science. ^63 THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. rJuLY, OF TERRESTRIAL OR HORIZONTAL REFRACTION, By Oliver Byrne, MHlheinatician. Rays of light passing from objects whetlier terrestrial or eel tial, proceed in curves concave to the earth, thus:—rays of light (lassing from objects T, S, to the eye of an observer at O, take curvelinear directions T o O, S A O, instead of the straight lines T O, S O. Fig. Now as the eye always traces the places of objects to the direction in
. The Civil engineer and architect's journal, scientific and railway gazette. Architecture; Civil engineering; Science. ^63 THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. rJuLY, OF TERRESTRIAL OR HORIZONTAL REFRACTION, By Oliver Byrne, MHlheinatician. Rays of light passing from objects whetlier terrestrial or eel tial, proceed in curves concave to the earth, thus:—rays of light (lassing from objects T, S, to the eye of an observer at O, take curvelinear directions T o O, S A O, instead of the straight lines T O, S O. Fig. Now as the eye always traces the places of objects to the direction in which the rays enter tlie eye, hence the observed elevations of objects are always greater than the true one, for the direction in which rays enter the eye is the direction of a tangent to the curve at the eye of the observer. The objects T, S, will appear in the directions of the tangents O T', O S'. The reason that the rays of light are bent in passing through the atmosphere or part of it, is because the air is densest at the surface and continues to decrease in density to the top of the atmosphere : it is well known that a ray of light becomes bent towards the perpendicular in being transmitted from a rare to a dense medium, therefore the rays passing through the atmosphere are being continually bent as they pass through a medium continually increasing in density. The increase in the angular altitude of objects by being observed in our atmosphere is called refraction : there arc two sorts of refractions, horizontal or terrestrial, and astronomical. Horizontal refraction affects objects situated in the atmosphere, astronomical re- fraction is that which affects the altitudes of the heavenly bodies. Refraction changes with the atmosphere, with regard to heat, cold, humidity, dryness, &c.; when tables of refraction are given they are calculated for a mean state of the atmosphere, in such a manner that they can be made to answer any other state of the atmosphere with some
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