Page:Science vol. 5.djvu/150

 SCIENCE.

��Ing cards, lie made, fn all, 2,il2? tri»U, ftTid obtained 789 successes instead of Ti2, which is the number that chance alone would lead him lo expect. Tbe pn>babi1il7 that Iha actual number of successes shall differ from the probable number in either dlreclioa by so much as 67 in 2,9-i7 trials (by?. in k trials, say) is approximately, —

�� ��which ^Tes In the present case;',,; Miul is to say. [here ia In rcalityonc chance in seventy of Jo great a deflation arising by .accident, while KIchet would make it fifty In fifty-one.

Wb repeat that many of Mr. Ricliet's experimeiils are interesting, and Ibe results very sl.rihing. It Is a pity [hat Iliey are not more effective than they are In placing Ihe question of mental sngge^lion upon a seiBntiGc linais. Cubistink Ladd Franklin,

��THE DIMENSIONS OF SHIPS.

I BAVz often thought, that, inpractUing tbeart of shlp-bultding, men have loo much neglected the study of the forms of the flsh which make the waters their permanent habitation, and are designed for the most part to attain the highest degree of velocity In the pursuit of their prey. No doubt, the case of a ship partly, and that of a Ash wholly, immersed, are not strictly parallel; but they offer very many points for comparison of which we may avail ourselves.

A fish makes use of its tail-fin as the clilef and nearly sole instrument of propulsion; and, in the adoption of the screw-propeller In preference to the old side-wheels, the steamers of the present day have secured a great advantage over the old forms. In the proportion of length to those of breadth and depth, however, although there has of late been some im- provement, there would appear lo be a lingering ten- dency to hold by the old mistaken idea that a ship was rather to be regarded as a wedge to cut the water tlian as occupying the space of a wave of displace- ment; and so we bave ships nine, ten, or even eleven times as long as broad, and twenty times Ihe length that Uiey have draught. Now, fenowitig as we do the magnitude of the skin -resistance iu ships, and Its smallness In the oily coata o( fishes, one would expect that the length of the latter would be grearer propor- tionally than that of the former, if ships were built in the proper form to secure a high velocity. But what is the fact? On an average of sixteen frc^h-water fish delineated In Daniell. I find that the extreme length, inclusive of the lall-fln, is four and Iwenty- two hundredths times that of the extreme depth ex- clusive of the dorsal and ventral fins. The average breadth will be perhaps one-half of the depth, mak- ing Ihe proportion to length about 1: 8.

Abatrustof B pspi^r by Ilr. J, 1'. Juule. ]iitblJ>tauil in the I'm-

��On an average of three species of whale, the nar- whal, Greenland shark, dolphin, and the porpoise, I find from Scoreeby and other authorities the propor- tion of either deptli or breadth to length to be about 1;4.7| they having nearly circular sections. There- fore It appears, that, while in ships the proportion of length to width of midship immersion la 6: 1, that, of the shark, the gKirpoise, or dolphin, is not moi*' than 1.5: 1.

Dr. Scoreaby, in his ' Arctic regions,' gives twflw miles per hour as the utmost speed of the whale; but Mr. liaiendeli gives it a velocity approaching twenty miles. I had an opportunity of witnessing the wonderful swimming-powers of the porpoise dut^ Ing a voyage to the Clyde In the Owl stearai 29th of June last. About eight a.m., the sea beii calm near the Mull of Galloway, we were beset by >! shoal of these animals, which raced with the ship, kept alongside for three or four minutes with greatest ease. They swam in twos and threes, i foot or two distant from one another, several proacliing within ten feet of the vesfel, which steaming at the rate of thirteen and tour-tenths statute miles per hour. If such a velocity can be maintained by the porpoise, with its comparatively bind I1gure>bead, we may surely expect a much higher velocity in the case of fish more obviously designed for speed.

My son tells me tlial in a voyage of the Ualvina from Leilh to London he had observed at night two fishes of about a yard long which kept for aconsider- able time In advance of the cutwater of the ship, be- ing visible by their phosphorescent light. The »hlp wai at the time steaming at the rate of Gfleen two- tenths statute miles per hour.

The investigation of the resistance of solldB inov>f1 Ing In fluids has been taken up theoretically bf'^ Thomson, Stokes, Eanklne, and practically by Fmudc^. who has found that the surface friction in long InnhJ ships Is more than fifty-eight per cent of the whol«> Froude recognized the study of the forms of anImaLJ life In guiding us to practical conclusions.

From the above considerations, I am inclined believe that a length of not more than five to one breadth would be better than the extreme proportlt of ships now in vogue, and that the greatest breadth should be considerably In advance of the midship.

��RECENT TRAVELS IN ARABIA.

��cull B>

��On nn excursion lo the great mountain Jebel Ag^,* the party camped at the entrance of the Tuarin vnl> ley, near the ruins of the little fortress El AsHr. Three palms grow here; and there Is a little spring whose temperature, 75° F., indicates the heat of the soil and rock In this arid region. Around the: were traces of cultivation and abandoned wells. a short distance the traveller was fortunate en

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