in general, is the deviation of a moving body from its direct course, occasioned by the different density of the medium in which it moves; or it is a change of direction occasioned by a body's falling obliquely out of one medium into another. The word is chiefly made use of with regard to the rays of light. See Optics Index, at Refraction.

REFRACTION of Altitude, the arc or portion of a vertical circle, by which the altitude of a star is increased by the refraction of light.

REFRACTION of Ascension and Declination, an arc of the equator, by which the ascension and declination of a star, whether right or oblique, is increased or diminished by the refraction.

REFRACTION of Declination, is an arc of a circle of declination, by which the declination of a star is increased or diminished by refraction.

REFRACTION of Latitude, an arc of a circle of latitude, by which the latitude of a star is increased or diminished by means of the refraction.

REFRACTION of Longitude, an arc of the ecliptic, by which the longitude of a star is increased or diminished by means of the refraction.

Terrestrial, is that which makes terrestrial objects appear to be raised higher than they are in reality, in observing their altitudes. The quantity of this refraction is estimated at one-tenth by Dr Mafkeleyne; at one-fourteenth by Le Gendre; and by De Lambre at one eleventh. But there can be no fixed quantity of this refraction, since it depends upon the state of the atmosphere, which is extremely variable. Some singular effects of this refraction have been noticed, and in particular the following, which were observed by Mr Latham at Hastings, during a very hot day, on which it was high water about two o'clock P.M. The day was also perfectly calm.

"On Wednesday, July 26, about five o'clock in the afternoon, while I was sitting in my dining-room at this place, which is situated upon the Parade, close to the sea-shore, nearly fronting the south, my attention was excited by a number of people running down to the sea-side. Upon enquiring the reason, I was informed that the coast of France was plainly to be distinguished by the naked eye. I immediately went down to the shore, and was surprised to find that, even without the assistance of a telescope, I could very plainly see the cliffs on the opposite coast; which, at the nearest part, are between 40 and 50 miles distant, and are not to be discerned, from that low situation, by the aid of the best glasses. They appeared to be only a few miles off, and seemed to extend for some leagues along the coast. I pursued my walk along the shore eastward, close to the water's edge, conversing with the sailors and fishermen upon the subject. They at first could not be persuaded of the reality of the appearance; but they soon became so thoroughly convinced, by the cliffs gradually appearing more elevated, and approaching nearer, as it were, that they pointed out and named to me the different places they had been accustomed to visit; such as the Bay, the Old Head or Man, the Windmill, &c., at Boulogne; St Valery, and other places on the coast of Picardy; which they afterwards confirmed when they viewed them through their telescopes. Their observations were, that the places appeared as near as if they were sailing, at a small distance, into the harbours."