ON THE ACTION OF WAVES AND CURRENTS. 519 
are continually cutting on their concave sides, it keeps cutting down the 
banks, preventing the occurrence of hard high banks and fixed channels. 
When the quantities of land water are small as compared with the tidal 
capacity of the tank, its direct action on the régime of the estuary is small. 
But that it may have an indirect action of great importance in connection 
with a tidal river is clearly shown. In the upper and contracted end of 
a tidal river the land water may well be sufficient to keep it open to the 
tide, whereas otherwise it would silt up. This was clearly the effect in 
the experiments H, 1 and 2, and by keeping the narrow river open the 
full tidal effect of this was secured on the sand at the top of the estuary, 
causing a great increase of depth. The effects of large quantities of land 
water, such as occur in floods, have not yet been investigated. 
13. Deposit of the Land Water in the Tidal River.—One incident con- 
nected with the land water in the tidal river is worth recording, although 
not directly connected with the purpose of the investigation. 
The land water, one quart a minute, was brought from the town’s 
mains in lead pipes. It is very soft, bright water, and was introduced 
at the top of the estuary. This went on for about three weeks. At the 
commencement the sand was all pure white, and remained so throughout 
the experiment except in the tidal river. At the top of the river a dark 
deposit, which washes backwards and forwards with the tide, began to 
show itself after commencing the experiment, gradually increasing in 
quantity and extending in distance. At the end of the experiment the 
sand was quite invisible from a black deposit at the head of the river and 
for 5 or 6 feet down; this, then, gradually shaded off to a distance of 
12 feet. Nor was it only a deposit, for the water was turbid at the top of 
the river and gradually purified downwards. 
On the other hand, in the precisely similar experiment, without land 
water the sand remained white and the water ciear right up to the top 
of the river. This seems to suggest that these experiments might be 
useful to those interested in river pollution. 
14, The International Congress on Inland Navigation—During the 
Fourth International Congress on Inland Navigation, held in Manchester 
at the end of July, the members were invited to see the experiments then 
in progress, the subject being one which was occupying the attention 
of the Congress. Advantage of the invitation was taken by many engi- 
neers, and especially by the French engineers. M. Mengin, engineer in 
chief for the Seine, stated in a paper! read at the Congress that in con- 
sequence of the paper (read by the author before Section G at Man- 
chester) the engineers interested had advised the Government to stop the 
improvement works on the Seine until a model having a horizontal 
scale of 1 in 3,000 was constructed, and the effect of the various improve- 
ments proposed investigated in the model, the model being then nearly 
ready, but the experiments had not commenced. M. Mengin paid 
several visits to the laboratory and carefully examined the apparatus and 
experiments, for which all facilities were placed at his disposal. 
15.. Recommendations for further Bxperiments.—Although theimmediate 
objects proposed for investigation this year have been fairly accomplished, 
there remain several general points on which further information is very 
important, besides the further verification of the criterion of similarity, 
and the determination of the final conditions of equilibrium with tidal 
rivers, already mentioned. It seems very desirable to determine the 
} International Congress on Inland Navigation, 1890. 
