212 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[July, 



the power spent (in tlieni is expended to no purpose. So it is 

 witli i);i(l(lle « lieels. A boat never jjrogresses in the ratio of their 

 revolutions, because of the yielding medium in which, and against 

 which, they act. They slip always — a result inevitable when mas- 

 sive solids wade through fluids. The distance between the Atlan- 

 tic steamers' docks, in Liverpool and New York, has been calcu- 

 Lited at 3,023 miles, but their paddles, in each trip, pass over a 

 space varying from a,000 to 8,000 miles. In steamers unaided by 

 sails, the disproportion is often greater. Now can this be modified, 

 by giving the paddles a better hold on the fluid they sweep through.'' 

 Ihe e.xperiments, tigs. 5, 6, 7, 8, 9, 11, 1'2, 14, l(j, and 17, furnish 

 replies to the interrogatory. 



The moral of the foregoing experiments is this: — As the pro- 

 pelling power of a jiaddle is greatest at its lower or outer extre- 

 mity, and diminishes to nothing at the surface, so its face should 

 enlarge with the dip, and be nothing, or next to nothing, above. — 

 Let rf, fig. 18, represent the end of an ordinary blade, or paddle. 

 Its upper part barely touches the water, and only for the moment 

 it is in the position shown But suppose it were immersed to the 

 line c, c, — say four or five inches — it would even then be no sooner 

 under, than above the surface again, so brief would be its immer- 

 sion. The lower edge, in the meanwhile, would sweep along the 

 extended curve there delineated. 



Fig. 18. 



Of what use, then, to make the upper part of a blade of equal 

 extent with the lower? Why accumulate surface where it is of 

 littie avail, and withhold it from where it is most wanted? — ex- 

 pending materials and power without any adequate return, if not 

 at an absolute loss. The quantity of water carried over a wheel, 

 is certainly greater by ordinary, than it would be by triangular, 

 paddles. The popular form and position of paddles are unphilo- 

 sophical, if viewed simply as propellers. Embrace the same area 

 in any other outline — in a circle, ellipse, square, pentagon, hexagon, 

 octagon, or other polygonous figure, and the propelling properties 

 would be increased, and the jar arising from their striking the 

 water also diminished. 



If the long paralellogram be preferred, because of the ready ap- 

 plication of wooden |)lanks, then is the principal sacrificed to an ac- 

 cessory — the greater to the less. If triangular, or other improved 

 blades, require the adoption of plates of metal, would it be wise to 

 reject them on that account? — But of this by-and-bye. We shall 

 see that thick wooden blades ought to be condemned on account 

 of defects inherent in them. 



But what is this expansion of the lower part of a paddle, and 

 contraction above, but Nature's own plan? In the tails and fins 

 of fishes, in wings of birds and insects, and especially in the 

 palmipeds, she has nowhere sanctioned a rectangular propeller. 

 All are inclined to equilateral, scalenous, or isosceletic triangles, 

 or are made up of them. Nor does she ever unite the levers that 

 work them to their sides. The junction is invariably at an angle, 

 and the reason is apparent — that the largest surface may have the 

 longest sweep. 



Witli this view, the bodies of fishes taper down to meet the 

 blades; retaining only sufficient muscle to work them. The other 

 day, I had an opportunity of sketching the following. I am 

 ashamed to acknowledge that, till then, I was ignorant of the 

 exact forms of these natural propellers, although most of them 

 had passed under my observation on a thousand occasions. Too 

 many of us spend no more thought on the infinitely curious and 

 instructive mechanisms submitted by the Creator to our inspection 

 daily, than does the ox on the vegetable glories he feeds on. The 

 sentiment applies not more to religious than to physical truths — 

 "Light shineth in darkness, and the darkness comprehendeth it 

 not." We grope, as if blind, for that which is patent before 

 us. 



The general outlines and proportions are given in the annexed 



figures; the dimensions, of course, vary with the age and growth 

 of in<lividuals. The figures denote the width and length of the 

 exjianded tails — the latter being taken from the termination of the 

 body, as shown by the curves, which reach more or less into the 

 tails — that is, to strengthen them where strength is most re- 

 quired. 



Fig. VJ. 



a— Cnd. 



i— Black Fish. 



c — Sea Bass, 

 rf— Porgy. 



g — Striped Bass. 

 A — Salmon. 



I confess I had no idea of meeting with figures so closely allied 

 to the artificial ones which I had found most eff'ectual as propellers. 

 With the exception of the first two, the whole approach to equi- 

 lateral triangles. 



In the absence of a more extended acquaintance with the minuter 

 aqueous and sub-aqueous organisms, the nearest of natural ana- 

 logues to steam-vessels seem to he the principal swimming-birds. 

 These glide through two elements at once. Their long and heavy 

 bodies, adapted to float gracefully on water, are provided with 

 organs of propulsion, placed far behind their common centres of 

 gravity — the cause tliat makes them such awkward travellers on 

 land. When a gale blows in the direction they wish to pursue, 

 like human navigators they take advantage of it; they spread 

 their wings to catch it, and are driven onward then, as steamers 

 are, by both wind and paddles. 



The reciprocating action, and the expanding and collapsing fea- 

 tures of their aqueous organs of progression, are supposed to be 

 unsuited to the magnitude, materials, and velocity of artificial 

 ones. Perhaps they are; but may not their contour be perfectly 

 applicable: since, when open, and in action, the circumstances of 

 the two bodies propelled — the bird and the boat — are not essen- 

 tially dissimilar? Now, tliere is a marked adhesion to the trian- 

 gular foi-m in the webbed feet of birds; showing that, in the judg- 

 ment of the Creator, such an outline is the best for the purposes 

 of their prop\ilsion. Nor does it a])pear that this outline has, in 

 any material way, been modified to meet other exigences. In the 

 feet of water-fowl it is almost identical with the tail of the sea 

 bass. The legs, or rods, that wield these ornithologic paddles, are 

 invariably united to them at their points, or angles, and clearly for 

 the reason already stated. 



Fig. 20 represents the foot of a petrel. It is a type of 

 all the swimming-birds' jiropellers. Few, except pro- 

 fessional naturalists, could distinguish between it and 

 the same organ in geese, ducks, gulls, swans, the alba- 

 tross, cormorant, diver, flamingo, &c., &c. Although 

 natural paddles are submerged when at work, and those 

 of our wheels emerge into air to repeat their strokes, I 

 doubt if a more efficient form could be given to the lat- 

 ter than the above. The cuspated extremity would ob- 



Fig. 20. 



