Aug. 8, 1884.] 



♦ KNOWLEDGE ♦ 



105 



far off a ship may be, which is hull down, and he will give 

 you an opinion based entirely on his knowledge of the 

 ship's probable size, and on the distinctness with which he 

 sees her. This opinion is often pretty near the truth ; 

 but it may be preposterously wrong if his idea of the 

 ships real size is very incorrect, and is sometiuies quite 

 wrong even when he knows her size somewhat accurately. 

 Any notion that the distance may be very precisely 

 inferred from the relative position of the hull and the 

 horizon line seems not to enter the average sailor's 

 head. During my last journey across the Atlantic we 

 had several curious illustrations of this. For instance, on 

 one occasion a steamer was passing at such a distance 

 as to be nearly hull down. From her character it was 

 known that the portion of her hull concealed was about 

 12 feet in height, while it was equally well known that the 

 eye of an observer standing on the saloon-passengers' deck 

 ou the City of Rome was about 30 feet above the water- 

 level. A sailor, asked (by way of experiment) how far off 

 the steamer was, answered, " Six or seven miles." " But 

 she is nearly hull down," some one said to him. " I didn't 

 say she warn't, as I know.s on," was the quaint but stupid 

 reply. Now, it might be supposed to be a generally-known 

 fact that even as seen from the deck of one of the ordinary 

 Atlantic steamers, the horizon is fully six miles away, the 

 height of the eye being about IS or 20 feet, and that for 

 the concealed portion of the other ship's hull a distance of 

 four or five miles more must be allowed : so that the man's 

 mistake was a gross one. And several other cases of a 

 similar kind occurred during my seven days' journey from 

 Queenstown to New York. 



The rules for determining the distances of objects at sea, 

 when the height of the observer's eye and the height of the 

 concealed part of the remote object above the sea-level are 

 both known, are exceedingly simple, and should be well 

 known to all. Geometrically, the dip of the sea surface is 

 eight inches for a mile, four times this for two miles, nine 

 times for three miles, and so forth ; the amount being 

 obtained by squaring the number of miles and taking so 

 many times eight inches. But, in reality, we are concerned 

 only with the optical depression, which is somewhat less, 

 because the line of sight to the horizon is slightly curved 

 (the concavity of the curve being turned downwards). 

 Instead of eight inches for a mile, the optical depression is 

 about six inches at sea, where the real horizon can be 

 observed. But, substituting six inches for eight, the rule 

 is as above given. Six inches being half-a-foot, we 

 obtain the number of six-inch lengths in the height of 

 an observer's eye by doubling the number of feet in 

 that height ; the square root of this number of six-inch 

 lengths gives the number of miles in the distance of 

 the sea horizon. Thus, suppose the eye of the ob- 

 server to be eighteen feet above the sea level ; then 

 we double eighteen, getting thirty-six, the square root of 

 which is 6 ; hence the horizon lies at a distance of six 

 miles as seen from an elevation of 18 feet. For a height 

 of 30 feet, which is about that of the eye of an observer on 

 the best deck of the City of Rome, we double 30, getting 

 60, the square root of which is 7 7; hence, as seen from 

 that deck the horizon lies at a distance of 7 71" miles. 

 If the depth of the part of a distant ship's hull below the 

 horizon is known, the distance of that ship beyond the 

 horizon is obtained in the same way. Thus, suppose the 

 depth of the part concealed to be 12 feet, then we take the 

 square root of twice 12, or 24, giving -1-9, showing that 

 that ship's distance beyond the horizon is -1 9-10 miles. 

 Hence, if a ship is seen so far hull down, from the hull of 

 the City of Rome, we infer that its distance is 4 9-10 miles 

 beyond the distance of the horison, which we have seen to 



be 7 7-10 miles — giving for that ship's distance 12 3-.5 

 miles. And with like ease may all such cases be dealt 

 with. — Newcastle Weekly Chronicle. 



THE SENSE OF TASTE. 

 By Geaxt Allex. 



ANIMALS eat, and, broadly speaking, one may say that 

 a better popular definition of what is most essential 

 to the idea of an animal as opposed to a plant could hardly 

 be found than this habit of eating. In all the highei 

 animals, at least, to eat implies a mouth — a special organ 

 for the reception and often for the trituration of the 

 natural food. This mouth is usually supplied with a tongue 

 or discriminative service, the object of which is to enable 

 the animal at once to distinguish between food that is good 

 for it and food that is useless or positively injuriou.?. The 

 sense by which the animal thus discriminates between 

 possible and impossible foodstuffs is called the sense of 

 taste. 



The lowest animals hardly need a sense of taste at all^ 

 at least iu the developed form here contemplated ; all is fish 

 that comes to their net ; they swallow and, if possible, 

 digest every bit of organic matter they happen to come 

 across in the course of their aimless peregrinations. Or, 

 rather, they swallow whatever is smaller than themselve,s, 

 and get swallowed by whatever is larger. Still, even in 

 these lowest depths of animal evolution, we get in a very 

 simple and undeveloped form some first faint foreshadowing 

 of the faculty which becomes specialised later on into the 

 sense of taste. When floating jelly-bag meets floating 

 plantlet or floating jelly-speck under the microscope, it 

 makes an effort to envelope the edible morsel all round with 

 its own matter. But when it meets mineral bodies or un- 

 eatable things generally, it either does not try to envelope 

 them at all, or if it coats them for a moment it soon rejects 

 them as of no practical use for its own purposes. These 

 simplest rudimentary animals, besides being all mouth and 

 all stomach, are also all nerve and all sense-organ. Every 

 part of them seems to possess in some feeble manner the 

 power of discriminating between what is food and what i& 

 useless. 



In the higher animals, side by side with the evolution of 

 a definite mouth, jaws, teeth, stomach, and digestive and 

 assimilative mechanism generally, the power of discrimi- 

 nating food has been specialised and localised in the tongue, 

 at the very front of the alimentary canal. In each species 

 of animal, natural selection has ensured that the nerves of 

 the tongue should correctly in the main inform the animal 

 what food-stufls were desirable for it, and what were 

 undesirable. Clearly if it were conceivable that a race of 

 animals should be so constituted that it liked poisons and 

 disliked nutritious substances, that race must rapidly die 

 out and leave no survivors. On the other hand, just in 

 proportion as a race finds the indications of its sense of 

 taste in harmony with the physiological effects of things 

 swallowed in that proportion must it tend (other things 

 equal) to prosper in life, and to hand on its own discrimi- 

 native powers to later generations. 



In the human species the gustatory tract has been^ 

 divided by Prof. Bain into three regions, each of which has 

 its own special and proper functions to perform in the 

 economy of tasting. The tip of the tongue is mostly 

 supplied with nerves which are really rather nerves of 

 touch than nerves of taste, and which are cognisant for the 

 most part of pungent, acrid, or saline bodies. Obviously 

 this arrangement conduces to the greatest safety of the 



