134 



SCIENCE. 



[Vol. V., No. 106. 



ing cards, he made, in all, 2,927 trials, and obtained 

 789 successes instead of 732, which is the number 

 that chance alone would lead him to expect. The 

 probability that the actual number of successes shall 

 differ from the probable number in either direction 

 by so much as 57 in 2,927 trials (by A in s trials, say) 

 is approximately, — 



VWo 



2pg. 



e-t 2 dt, 



which gives in the present case tV; that is to say, 

 there is in reality one chance in seventy of so great a 

 deviation arising by accident, while Richet would 

 make it fifty in fifty-one. 



We repeat that many of Mr. Richet's experiments 

 are interesting, and the results very striking. It is a 

 pity that they are not more effective than they are in 

 placing the question of mental suggestion upon a 

 scientific basis. Christine Ladd Franklin. 



THE DIMENSIONS OF SHIPS. 



I have often thought, that, in practising the art of 

 ship-building, men have too much neglected the study 

 of the forms of the fish 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 fish 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 chief 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 to 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 

 than as occupying the space of a wave of displace- 

 ment; and so we have ships nine, ten, or even eleven 

 times as long as broad, and twenty times the length 

 that they have draught. Now, knowing as we do the 

 magnitude of the skin-resistance in ships, and its 

 smallness in the oily coats of fishes, one would expect 

 that the length of the latter would be greater 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 fresh- water 

 fish delineated in Daniel 1, I find that the extreme 

 length, inclusive of the tail-fin, is four and twenty- 

 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 the proportion to length about 1 : 8. 



Abstract of a paper by Dr. J. P. Joule, published in the Pro- 

 ceedings of the Manchester literary and philosophical society. 



On an average of three species of whale, the nar- 

 whal, Greenland shark, dolphin, and the porpoise, I 

 find from Scoresby and other authorities the propor- 

 tion of either depth 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 is 5: 1, that 

 of the shark, the porpoise, or dolphin, is not more 

 than 1.5: 1. 



Dr. Scoresby, in his ' Arctic regions,' gives twelve 

 miles per hour as the utmost speed of the whale; 

 but Mr. Baxendell gives it a velocity approaching 

 twenty miles. I had an opportunity of witnessing 

 the wonderful swimming-powers of the porpoise dur- 

 ing a voyage to the Clyde in the Owl steamer on the 

 29th of June last. About eight a.m., the sea being 

 calm near the Mull of Galloway, we were beset by a 

 shoal of these animals, which raced with the ship, and 

 kept alongside for three or four minutes with the 

 greatest ease. They swam in twos and threes, at a 

 foot or two distant from one another, several ap- 

 proaching within ten feet of the vessel, which was 

 steaming at the rate of thirteen and four-tenths 

 statute miles per hour. If such a velocity can be 

 maintained by the porpoise, with its comparatively 

 bluff figure-head, we may surely expect a much higher 

 velocity in the case of fish more obviously designed 

 for speed. 



My son tells me that in a voyage of the Malvina 

 from Leith to London he had observed at night two 

 fishes of about a yard long which kepj for a consider- 

 able time in advance of the cutwater of the ship, be- 

 ing visible by their phosphorescent light. The ship 

 was at the time steaming at the rate of fifteen and 

 two-tenths statute miles per hour. 



The investigation of the resistance of solids mov- 

 ing in fluids has been taken up theoretically by 

 Thomson, Stokes, Rankine, and practically by Froude, 

 who has found that the surface friction in long iron 

 ships is more than fifty-eight per cent of the whole. 

 Froude recognized the study of the forms of animal 

 life in guiding us to practical conclusions. 



From the above considerations, I am inclined to 

 believe that a length of not more than five to one of 

 breadth would be better than the extreme proportions 

 of ships now in vogue, and that the greatest breadth 

 should be considerably in advance of the midship. 



RECENT TRAVELS IN ARABIA. 



From the recently printed account of Mr. Charles 

 Huber's mission in Arabia we cull some notes of gen- 

 eral interest. 



On an excursion to the great mountain Jebel Aga, 

 the party camped at the entrance of the Tuarin val- 

 ley, near the ruins of the little fortress El Asfar. 

 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 ruins 

 were traces of cultivation and abandoned wells. At 

 a short distance the traveller was fortunate enough 



