THE RANGE OF VISION. (La Nature.)

Waikato Times, Volume XXVI, Issue 2119, 6 February 1886, Page 2 (Supplement)

THE RANGE OF VISION. (La Nature.)

In perfectly clear weather the distance from which itn object of small size (a m»n for example) is visible to the naked eye cannot exceed about three and a half miles, when the object is seen in relief against a white background. It may be said that an object is only visible when its movement is perceptible to the naked eye. From Cape Hode, situated near Havre, it is possible to perceive a fisherman or hunter walking 1 upon the sand banks of the Seine. From the valley of the Grindelwald, in Switzerland, it ia possible to Bee a tourist upon the Jungfrau or Wetterhoru. The distance can be innreased by means of a simple opera glass. Fiom the Havre jetty persons may thus be "-een in very clear weather, upon tlie beach of Trouville, at a distance of eight and a half miles. I say pee, and n>t recogni-e; and yet certain fisherwomen of Villerville, have found it possible to recognise their husband's boat starting from Havre six miles distance. \t the last shooting match at Havre, Messrs Bigot and Pelot each made a seiies of bull's eyes at nine hundred yards distance—a fact that, besides great skill, supposes a very strong sight. In tropical seas captains agree in sayinj; that from the deck of their .ships the distance that is visible around them is six leagues. In temperate zones the dis tance is less. In many cases the earth's curvature presents an obstacle to the range of vision, and yet this does not always appear to be so. Captain Duclos, of Havre, tells me that once, while becalmed off Madeira, he could not perceive the island during the day, but in the morning and evening observed it at a distance of twenty-two leagues. Pro fessor Morel, of Paris, informs me that while at Nice he perceived the profile of the mountains of Corsica and even made a sketch of it. I myself while near Dungeness, England, saw houses that weref-itu ited in the environs of Boulogne-sur-Mcr, France. In fine weather we cannot see Lion or Luc-sur-Mur from the Havre jetty, and yet there are days when both these localities become visible. I have found while on a steamer in ordinary weather that the s.iici lecalities become visibly at tho mi.ldle of the route. Oa returning, tho electric lights of the Havre jetty become visible at the same point. There are, then, days on which, in certain weather, und despite the curvature of tho earth, the distance of visibility is double 1 or more than doubled. The phenomenon is expl lined to us by a well known law of physics. If we throw a rom into an empty ve^el, it will be hidden by tho edge of the latter, at a certain distance : but if we fill the vessel with water, the coin will become visible. We have here a ca«o of refraction, such as is expldiued in elementary works on physics. Everyone also knows the theory of the mirage put forth by the celebrated Mon if c, who explains tlie phenomenon as duo to a diminution of the air's density in contact with the superheated earth. A contrary tlieory will explain the mirage at sea. While the sun is making the atmosphere intensely hot, the sea and the strata of air in contact therewith remain relatively cold, and these strata become superposed in the order of their density. A luminous ray emanating from the sea will pans from one stratum into another of less density, there will be a refraction and an object beneath the horizon will be seen above it. This theory supposes two conditions, to wit, a heating of the atmosphere, while the sea and earth remain relatively cold, and a calmness of it to permit its strata to become superposed in the order of their density. It is precisely when these two conditions are fulfilled that the phenomenon of the mirage occurs. On such days ships rise instead of descending in measure as they recede. As the horizon is perceived by direct visibility, a ship is finally seen above the horizon, as if ifc were suspended in the air. It is the famous " phantom ship," familiar to sailors —a visible ship in its natural, upright position. If atmospheric conditions were favourable, a second ship would be seen above the first, <fee. Certain mariners worthy of have assured me that they have seen as many as seven superposed ships.

EASILY UONK. . . " Maggie. I doa'fc like to see this dust on the furniture." "AH right, mum. I'll shut the blinds right away." The mate of a ship, at the critical moment of a storm, shouted out : " Let go the topsail halyards !" "I ain't a-touching 'em sir," was the reply of a newly shipped "sailor."

ADAM NOT A DRAMATIC IIERO. " I wonder why Adam has never been made the hero of some play or drama f" remarked Ralph Renton, a Galveston nabob, to John Irving, who is of a literary turn of mind. " The reason why Adam is not available as a hero of a play," replied Irving, " is simply because it is not possible to mix him up in a social icandaj with 5.0m.9 wwrie£ wauwn,,"