986 
FOREST AND STREAM. 
[Dec. i7, 1910. 
In both instances the particles or globules of 
which water is composed are thrown into con¬ 
fusion by these right-angle currents; the fila¬ 
ments of cohesion being broken by the con¬ 
fusion of the globules and dispersion of attrac¬ 
tion, the water becomes obedient to the law 
of gravitation. It is obvious that if a solid 
body can be driven through water which has 
lost its properties of continuous cohesion, there 
would be an enormous saving of propelling 
power. 
Referring to instances where there is no 
cuirass armor, and where the species are large 
enough to enable us to judge by our visual 
organs, it may be seen that this method has 
been adopted and is accompanied by remark¬ 
able speed. The huge scales of the tarpon, the 
sea perch, etc., afford this opportunity. They 
are quite thin, and overlap. The surface, which 
is perfectly smooth, would be even were it 
not for the fact that the scales are convex, 
the vertex of each scale being elevated to such 
an extent from the base line that the surface be¬ 
comes one of unevenness. One noticeable feature 
is that the largest and most convex scales are 
placed at the thickest part of the body, where, 
during displacement, the hydraulic pressure 
would be greatest. Another feature is that, 
the scales being convex, the broken-jointed 
principle of imbrication prevents there being a 
series of longitudinal striae extending from the 
head to the caudal fin, for alternate convexities 
intervene on the lines where the channels would 
otherwise be. This device would enable each 
convexity to act independently on the water. 
The rhomboidal ganoids would have similar 
striation, though of course not so wide or so 
deep, where the water would press in and 
adhere, were it not that the scales are arranged 
in oblique rows. This method would also en¬ 
able each rhomboid to act on the water inde¬ 
pendently. 
Many species of fish have smooth skins 
without scales, while others have a similar 
smoothness of surface but are provided with 
thin small scales. In all such cases there is, 
during the death-struggle, a copious exudation 
of slimy matter which is supposed to act as a 
lubricant for the water to slide on in the same 
manner that two surfaces of metal slide on 
each other when oil is applied to prevent 
friction. There cannot, however, be any 
analogy between the modus operandi of the one 
and the other, for, if water is poured on a fresh¬ 
ly caught fish, such as those referred to, this 
matter washes away and mixes with the water. 
This would show that the water must adhere to 
the slime during the swimming movement, and 
that it must be left behind as it was forced 
through the skin. This process would, no 
doubt, prevent the particles of water from ad¬ 
hering to the body of the fish and holding it 
in check, but, the slime being left behind, the 
supply would soon become exhausted, and, 
therefore, could only be used during the ex¬ 
citement of danger, or in the pursuit of prey. 
This hypothesis would account for what may be 
observed when a grebe pursues one of these 
species under the water. The fish swims with 
great rapidity for a short distance, but the speed 
diminishes so rapidly that the grebe secures the 
fish with very little effort. In a similar manner 
a kingfisher will strike several times at a trout 
in shallow water, after which the helpless crea¬ 
ture is secured. When the sea is calm and the 
sun is shining, you can always tell at a distance 
if mackerel have been caught in a trap net 
which has been set for them, for, in their efforts 
to escape they exude large quantities of iri¬ 
descent slime which floats over them on the 
surface of the water and reflects prismatic 
colors. 
These observations are made for the purpose 
of showing that water will not slide on any 
substance that we know of. 
I shall also call attention to the movements 
of a ganoid which I had an excellent oppor¬ 
tunity of examining at the Aquarium in New 
York. The species was a sturgeon, sixteen feet 
in length; and being alive in a large tank of 
clear water, the operations of the tubercular 
scutes could be discerned. There were five 
longitudinal rows of these shields, the largest 
being at the thickest part of the body. Each 
shield in its row is separated by an open space 
and is beveled to the uneven skin, making 
them all independent of each other. I believe 
I am justified in stating that any one wifh a 
mechanical turn of mind would come to the 
same conclusion that I did, which was that this 
fish could not move an inch through the water 
without bringing these shields into operation in 
their action of throwing currents of water at 
right angles to the line of movement. 
Alluding to the ascertained fact that water 
will not slide on any moving solid substance 
that we know of, I would like to explain that 
this property which water possesses applies 
particularly to what in hydraulics is called still 
water. 5 The action, however, which takes place 
when still water is divided by two moving sur¬ 
faces of wedge form, and that which takes place 
when these surfaces separate water which is in 
a condition of confusion or vibration, is en¬ 
tirely different. In the one'case the still water 
possesses continuity of cohesion, and in the 
other case the confused water does not, as is 
shown by the effect of heavy rain on high 
waves which are composed of still water 6 (ex- 
°A wave is only an undulation of still water. 
cept where the caps are broken by the wind). 
As we know, the molecules of water form them¬ 
selves into globules which are practically in¬ 
compressible, and when the filaments of co¬ 
hesion which bind these globules together are 
disrupted by the confusion of the globules, then 
the globules do not slide on each other, or on 
the moving body; they roll, and by so doing 
they reduce the friction to a negligible quantity. 
They cannot roll as long 'as the connecting 
threads of cohesion remain intact, for, until dis¬ 
persion of attraction takes place in the globules, 
they are drawn after each other by any mov¬ 
ing body, which being smooth and even, creates 
no surface disturbance adjacent to the moving 
body. 
In a case where an imbricated surface—similar 
to the slated roof pattern of some ganoids—is 
propelled through water, the confused stratum 
of water adjacent to the moving body would be 
equal in thickness to the unevenness which the 
pattern of imbrication shows, 1 the w^ter-shed 
being from the head to the caudal fin. In like 
manner where in nature we find convex scales, 
as in the tarpon and the sea perch, the vibrat¬ 
ing stratum would be equal in thickness to the 
convexity of the scales. It appears self-evi¬ 
dent that such would be the case, and, if so, 
then the propelling power required to produce 
the disturbed stratum would be a mere frac¬ 
tion of that which is lost by allowing the law 
which governs the continuity of cohesion in 
water to come into operation. 
That this subject deserves more considera¬ 
tion than it has hitherto received is beyond dis¬ 
pute, for its commercial importance is incalcul¬ 
able. If the problem is perplexing and difficult 
to understand, we render it more so by bind¬ 
ing ourselves mentally to preconceived ideas 
which are at variance with the object-lessons 
which we find in nature. In support of this 
assertion we have only to examine the subject 
conversely and we find that the action of “still 
water,” when moving over inorganic matter, 
produces for itself a surface pattern of least re¬ 
sistance which is unlike what our imagination 
would lead us to suppose. It may be noticed 
that when undisturbed water moves over a bot¬ 
tom of fine sand it does not make the sand 
smooth or even as might be expected. The 
law of adhesion in water comes into operation, 
and the surface of least resistance for the water 
to move on is produced on the sand by the 
moving water adhering into formation a series 
of undulations which are always at right angles 
to the direction in which water was or is mov¬ 
ing. It will not do this when the particles are 
in confusion, for then scouring takes place and 
the sand is carried away with the water. A 
steady wind which blows for some time from 
5 Still water means undisturbed water, and may be 
moving- in any direction. 
T Thick overlapping slates give more unevenness than 
thin ones. 
the same direction over the fine dry sand where 
the surface is flat does the same thing. It 
forms a pattern of least resistance in the shape 
of undulations. I dare say many people have 
observed that when you go to bathe in the sea 
in fine weather, where the tide comes in and 
goes out over a bottom of fine sand, the sand is 
not even, no matter how great the pressure 
may be which the depth of water gives, nor how 
rapidly the tide moves. Your bare feet walk 
over a series of undulating ridges which are 
all identically the same in formation, and which 
are always at right angles to the movement of 
the water. This, however, is not the case in 
stormy weather, for the incoming waves break 
form when they touch bottom, and the sand 
ridges are scoured in the direction of the shore. 
These facts go to prove that the natural surface 
of least resistance for still water to move on is 
not one which is smooth and even as it is in 
a metal cylinder where a piston slides. 
In the case alluded to, where the unconfined 
"water moves over the fine sand after the sur¬ 
face of least resistance has been formed, there 
cannot be adhesion or appreciable friction, for 
the slightest touch which a finger can give de¬ 
forms the undulations of the sand, whereas the 
moving water does not. 
If these facts are admitted, it would then ap¬ 
pear to be a physical impossibility for a smooth 
and even surface to be the one of least re¬ 
sistance when it is propelled through still water, 
for conversely it will not bold good. 
The fossil ganoids which existed during the 
formation of the coal-measures are described in 
the American Cyclopedia. I quote the passage 
referring to them and also to their present rep¬ 
resentative: 
In the American Cyclopedia, Vol. VII., under 
the head of “Ganoid,” this passage occurs— 
quoting extracts from the writings of Agassiz 
and Hugh Miller: 
“Ganoid fossil scales, whether angular, 
rhomboidal, or many-sided, are imbricated like 
the slates of a roof. * * * 
“These reptilian fishes attain their greatest 
number and largest size during the carbonifer¬ 
ous period, and were remarkable both for their 
formidable offensive weapons and their strong 
defensive armor. * * * Indeed no animal 
ever had more powerful teeth than the Ganoid 
Rhizodus of the coal fields. * * * These 
reptilian fish must have been forty feet in 
length.” 
“Gar pike Lepidosteus.” 
“It is the only genus of its family, and there 
are more than twenty species, all American. 
“As in other ganoids, the body is covered 
with smooth enameled scales of rhombic form, 
arranged in oblique rows, and so hard that it 
is impossible to pierce them with a spear. 
* * * It leaps often out of the water in 
pursuit of its prey and is so swift and strong 
a swimmer as to stem the most furious rapids. 
It attains a length of five feet. The alligator 
garfish has a shorter head, the jaws forming 
not quite half the length, broad and flat above. 
The skin is rough, the scales imbricated and 
sculptured. It inhabits the Mississippi and 
Ohio rivers and their tributaries, and is usually 
from four to six feet long.” 
Many interesting fossil specimens of the 
Lepidosteus ganoids may be seen in the Crom¬ 
well Road Museum, London. Their present 
representatives are numerous in Lake Erie, and 
differ only in size; their speed is phenomenal. 
I shall conclude by stating that it appears 
self-evident that the “horny protuberances” 
which may be seen on the covering of the al- 
bacore would impede locomotion if they were 
not intended to serve the purpose of vibrating 
the surrounding water, which they inevitably 
would do when forward movement took place. 
And yet this is one of the fastest of ocean 
travelers. The same principle may be seen car¬ 
ried out on the carapace of a soft-shelled crab 
or on a hand-bag made of alligator’s skin. 
A. Canoeist. 
The Forest and Stream may be obtained from any 
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regularly. 
