TRANSACTIONS OF SECTION G. 687 
of commerce flowing into and out of the Port of London, has claims on the attention 
of every individual concerned in the commercial prosperity of the kingdom. I 
propose to meet these difficulties by constructing across the river from Gravesend to 
Tilbury a dam or barrage similar to that across the Nile; the foundation of the 
dam, constructed of granite and mass concrete, will be in the chalk, and on the top 
will be a roadway for carriage and ordinary road traffic; the dam will be provided 
with locks, four in number, each provided with interral gates in addition to the 
outer ones, in order that these locks may be worked in long or short lengths to suit 
the traffic, The lengths provided in this way will be 300 feet, 500 feet, 700 feet, and 
1,000 feet, and the widths from 80 feet to 100 feet, which will suit both present and 
future steamships. It will be easy to lock the number of vessels passing up and 
down the river (which averages 220 per day), many of which are small craft; but 
the lock accommodation could lock three times the number if necessary; the great 
advantage to the shipping interest being that, instead of waiting tides at Graves- 
end, each vessel as she arrives can be locked in a few moments without delay. 
The lock will be worked by electricity generated and obtained from dynamos 
operated by the fall of water flowing over the dam; a pilot-tower will be fixed 
from which the traffic will be worked and regulated and locks, movable bridges, 
&c., controlled. 
A system of signalling from the barrage to the upper reaches of the river will 
be employed to notify any heavy freshet coming down the river, so that the 
sluices may be regulated to maintain the required level in the river to the proposed 
depth of 30 feet, as well as to secure the approaches to the locks, 
The dam will provide a fresh-water basin to the Trinity high-water mark, and 
the present docks will be accessible at all hours of the day or night irrespective 
of tides. The unsightly and foul-smelling mud-banks now laid bare twice in the 
twenty-four hours will no longer disfigure the river; a fresh-water lake forty 
miles long will be available for boating and pleasure traffic—thus opening up a 
new source of recreation and physical exercise to the teeming millions of the 
metropolis—and provide a supply of water for the new Water Board without going 
to Wales at a cost of not less than 24,000,000/. for an additional supply; the 
extension of works on both banks of the river will afford facilities for employment 
to our working population, and enable them to spread and so relieve the conges- 
tion of the ever-increasing East End population. 
In connection with the dam I propose to construct a tunnel, which will be 
formed in the solid monolith as the work proceeds, connected with the exist- 
ing railways in Essex and Kent, which will enable the military and naval authori- 
ties to utilise their base of warlike stores in Woolwich, Sheerness, and Chatham on 
our north-east coast, should the necessity arise, thus saving both time and expense. 
The dam from a strategic point of view affords a valuable solution of the 
question of the Thames defence by effectually blocking the river, and prevents the 
approach of submarine or other ‘raiders’ ; incidentally it provides a grand harbour 
for the fleet and a protection against invaders; and, lastly, the cost is only 
4,000,000/., as against 37,000,000/. proposed, besides which must be set off pro- 
spective enormous outlay for water-supply, reservoirs, and other matters, which will 
become unnecessary if this scheme is adopted. 
5. Testing Alternate-current Motors by Continuous Current. 
By Wituiam Cramp, A.M1.2.E. 
Since an alternating magnetic field may be resolved into two equal rotating 
fields, each of 0°7 times the value of the original field, it follows that there is a 
close connection between the behaviour of an alternate-current motor on its 
normal supply and that of the same motor having the stator supplied with a con- 
tinuous current of the proper value, while the rotor is driven round at the proper 
speed by some independent means. 
As an example of this consider a repulsion motor. It may be shown that such 
a motor is a special case of the single-phase alternator, whence the laws govern- 
