Macxitn.—Protection of River Banks. 145 
river threatens to form a new channel, leading directly through the town, as 
the lowest portion of the plain. The construction called a “dam” was 
erected some two years ago, at the point Z, (plan No. 1) and has not only 
diverted the stream into the * new ” channel, but raised the bank of shingle 
behind and below it. The old bed is gradually silting up. Had solid 
planking been put in to divert the current, it would have got undermined 
almost immediately, and the shingle been carried on and deposited where 
it would do harm. 
The theorem is as follows :—If a current will carry shingle, when 
travelling at the rate of six or seven miles per hour, but will not, if the 
velocity is decreased to say four, then, anything so decreasing it, will force 
it to drop the shingle; and, what is of more importance, at the point where 
itis so decreased. The invention I have to describe was suggested to Mr. 
Druslin, by observing and experimenting on the action of one log floating 
and moored diagonally across a current, by which it was seen that the 
surface current was deflected. It then became clear that a series of logs 
moored at certain distances from the bottom above one another, and so fixed 
to upright posts that they would float or rise with the flood, would not 
only divert the current by producing a resultant between the downward 
velocity and the resistance, but by forming eddies below the logs, and 
decreasing the velocity, cause the deposit of all the shingle. The water 
here in flood time is about twelve feet deep, and there is a series of frame- 
works of five logs each, averaging twenty-eight inches in diameter, placed 
diagonally across the stream, sloping from the bank at an angle of 135 
degrees down stream. It will be seen that these logs, fixed in the following 
manner, check about half the volume of current and divert the remainder. 
Piles of very heavy timber are driven into the bed of the river; the first 
horizontal log lies on the bottom, the next about a foot above it, and so on 
to the surface; the whole series is so arranged that the top log always floats; 
in fact the structure is so buoyed that it rises on the piers with the flood. 
The accompanying plans will show the construction. Reference to plan No. 
8 will show how the stones and sand get piled up during a flood, so high as 
to reach within a short distance of the surface, while in front of the logs 
there is a raging torrent. There is one defect about this invention, which 
led many people to condemn it at first. During flood-time a bank of shingle 
is raised, averaging eight feet (see along the line m n on plan No. 1), but 
during its subsidence, and until the next flood occurs, the river is acting on 
it, and cutting it away. But plans are now devised for placing a wing-wall 
of planks, perpendicularly to the horizon, in a frame in such a manner 
that they will drop into any holes made beneath them by the water, 
thus keeping the bank of shingle intact. There is no doubt in m mind 
