72 
NATURE 
[ May 26, 1870 
THE ABRADING AND TRANSPORTING 
POWER OF WATER 
III.—PRACTICAL CONCLUSIONS 
Reyne on two former occasions, when treating of 
the abrading and transporting power of water 
(which is supposed to increase as the velocity increases, 
but to decrease as the depth increases), dwelt on the 
mechanical property of water, and shown how it rolls 
rather than slides: the following conclusions may be 
arrived at :— 
1. That all particles of water have an affinity to each 
other as well as to other bodies, and that force is 
required to separate them ; 
It. That friction sets these particles rotating in all 
directions in larger or smaller circles, and that the 
friction or force increases in some proportion to 
the area of surface exposed ; 
111. That this rolling motion becomes rarer the 
larger the diameter of the circles may be, that is, 
the resistance decreases as the depth and breadth 
of a stream increase, or in other words, the velocity 
increases proportionally to the “hydraulic mean 
depth ;” 
Iv. Lastly, that any increase to the rapidity of this 
rotatory motion, must increase the abrading and 
transporting power of water, by enabling it to 
remove from the channel of a stream grains of 
solid matter, and hold them in suspension. 
The following deductions are arrived at :— 
1. That a smooth surface offers the smallest area for 
the water to attach itself to, and fewer irregularities ; 
consequently the rotatory motion given to the water is 
reduced to a minimum, that is, the power expended is 
least, or the friction among the particles of water flowing 
through a smooth uniform channel is less than when it 
flows through an irregular and rough one. 
2. That in the lines of a ship not only should there be 
no sudden changes in direction, but the surfaces should 
be as smooth as possible. 
3. That the area of this surface should be as small as 
possible ; hence convex lines are preferable to concave 
ones, as with the same area they afford greater buoyancy, 
while there would be less friction for the water to roll 
along a convex surface than a concave one. 
4. That additional length given to a ship, leaving out all 
other questions, must retard a ship passing through the 
water, by increasing the area exposed to friction ; conse- 
quently there is probably some limit owing to this increased 
resistance, where the length midships should not exceed 
certain proportions of the midship section. 
5. That a ship passing over shallow water must be 
retarded, as the diameter of the vertical circles revolving 
under her bottom must be less than the diameter of the 
circles where the water is deep; hence the smaller circles 
will be set in quicker rotation, and therefore loss of power 
ensues. 
6. That the same will be the effect from the same cause 
where the channel is narrow and contracted. 
These deductions apply to cases where the abrasion 
may be considered “nil,” such as the discharge of water 
through pipes, and the sailing of ships; and the practical 
conclusion is, that for pipes with glazed surfaces, and ships 
having coppered bottoms, the water passes with the least 
friction.* In the case of ships, sfeed is not the only 
* On reading over the above conclusions to an experienced ship-builder 
here in London, he said that one of the reasons why Aberdeen clipes sailed 
so fast, was owing to the smoothness of the ships’ bottoms, which were first 
planed before the copper was put on. He also remarked that where the 
copper is very smoothly put on, the first place where the sheet wears through 
is just behind where the sheets overlap, showing that even an irregularity of 
ys of an inch causes an extra action, not as might be supposed at the point 
of greatest obstruction, but just beyond it, proving that there must be this 
whirling motion which causes this abrasion. This gentleman also observed 
that experience showed that the speed of a ship chiefly depends on the fine- 
ness of the lines of the after rim of a ship, and that “‘ingoing” or concave 
lines should be avoided if possible. 
question to be considered, so the subject becomes very 
complicated,and though believing in the general soundness 
of the above deductions, the solution of these problems 
may be left to the naval architect to consider. 
Viewing the subject on the large scale, very im- 
portant conclusions are arrived at from these facts— 
namely, that the depth of a river depends on the 
nature of the materials it has got to transport; thus those 
which have to carry down coarse sand should be broad 
and shallow, while those which have to convey fine mud 
would naturally be narrow and deep. And as this depends 
on the geological nature of the catchment basin of the 
river, are we not naturally led to the conclusion that where 
we find rivers navigable, the rocks of the catchment 
basin which predominate are of an aqueous formation, 
while those rivers which are difficult of approach from the 
sea must drain a country where crystalline rocks pre- 
dominate? Judging, therefore, on this hypothesis, are we 
not right in conjecturing that the rocks of Central India, 
and also of that vast, but hitherto almost unexplored, 
country, Central Africa, must be generally of a crystalline 
nature? 
This interesting question, however, like that of the best 
form of ships, had better be left for the consideration of 
the professional inquirer, whose investigations lead him to 
study that branch of geology which treats of the denuda- 
tion of rocks now going on on the earth’s crust, and the 
deposits now being formed. I pass on to those questions 
which affect the hydraulic engineer, and they are so 
numerous that it would be difficult even to enumerate and 
classify them, while their importance is so great that it 
can hardly be over-estimated. On this occasion only one 
or two of the more prominent subjects will be glanced at, 
more for the purpose of leading to future investigation, 
than to lay down rules for guidance, which at this present 
stage it would be premature to attempt. 
From the foregoing remarks, suggestions, and deduc- 
tions, it may be supposed that there are certain laws of 
nature which adapt each case to its own particular circum- 
stances. Take, for example, the course of a river. It has 
been before said that streams which have to transport 
coarse, solid matter, such as sand, are usually broad 
and shallow, while those which convey chiefly fine mud 
are deep and narrow. The reason why those streams 
which convey a large proportion of sand should be broad 
and shallow, is that the water has thus sufficient power 
to hold the solid matter in suspension ; and to still further 
aid them in this, it will be often observed that Nature 
generally gives such rivers comparatively speaking straight 
channels, in comparison to those which convey fine 
mud. The object in this case would appear to be that 
Nature in the former instance takes the shortest route, so 
as to obtain as great a fall as possible in the bed of the 
stream ; while with the deep muddy stream, to prevent the 
water rushing off too fast, and so to keep up the sur- 
face of the stream to a level with the banks, or in floods 
often above them, Nature takes her tortuous courses, 
and is thus enabled year after year to deposit those fine 
grains of mud which add so much to the fertility of the 
soil. 
So evidently is this the case, that in Egypt the irrigation 
canals are all carried in a zigzag direction, so as to check 
the velocity, and prevent the coarser particles of solid 
matter from being transported, while at the same time the 
surface of the water is kept at a sufficient elevation, so as to 
admit of easy irrigation. Thus, probably, Joseph, or who- 
ever started irrigation in the land of the Pharaohs, took a 
leaf out of Nature’s book; and it is by the study of this 
volume that the engineer of the present day will be most 
certain to arrive at satisfactory results. 
That rivers have certain general principles by which 
they are governed, as to breadth, depth, slope, velocity, 
and load of solid matter held in suspension, it appears 
reasonable to suppose ; and any change introduced in any 
