TRANSACTIONS OF THE SECTIONS. 227 
deep, and therefore the upperside of each sluice when fully open is 4 feet sub- 
merged under water. When all the sluices are open to the fullest possible extent, 
the aggregate water-way is but one third of the sectional area of the river. Two 
thirds of the water-way is permanently shut: T'o meet this great contraction the 
Government engineer has designed very large excavations; and he provides for a 
head or difference of level between the water at the upper and lower sides of the 
river of about 2 feet. 
At Killaloe the existing fall in the surface of the flood-water is 63 feet in a 
distance of 4400 feet, being at the rate of 7} feet per mile. Out of this fall of 63 
feet, the head which the engineer provides for propelling the flood-water through 
his sluice-opes is 2 feet 2 inches. Thus a third of the whole available fall is 
appropriated to the weir, and two thirds merely to the river. 
y using a regulating-weir wholly movable, such as the “barrages mobiles,” of 
which forty have been in action in the rivers Seine and Yonne for several years, 
no head is required, none of the natural fall of the river is wasted, the whole is 
disposed along the surface of the river to actuate the current. Of course far less 
excavation is then required to carry off the flood-waters. 
At Killaloe on the Shannon the Government engineer has been obliged to 
estimate for the following excavation :— 
177,785 cube yards of rock at 2s... £17,778 
59,515 cube yards of clay at 9d... 2,231 
Amount .iiieesias isases £20,009 
With present prices that would cost £25,000. 
- The existing channel, with the surface of the river above at a level that will 
injure no crop, affords a fall at the rate of 64 feet per mile, and a cross sectional 
water-way 430 feet broad and 6 feet deep. This will carry 1,230,000 cube feet of 
water per minute, The greatest quantity of flood-water he proposes to provide for 
the discharge of there is 1,200,000 cube feet per minute. There, with a wholly 
movable weir, the existing channel is sufficient, and the proposed excavation is not 
necessary. Therefore works for the improvement of the Shannon at Killaloe, 
sufficient to improve the drainage of the division of the river above it without 
injuring the division below it, may be designed at a cost certainly £20,000 less 
than the estimate recently made by the Government engineer, by using a wholly 
movable regulating-weir. 
Proportionate savings may be effected on the same principle in the other divisions 
of the river. 
It has been stated that a wholly movable weir at Killaloe would injure the 
navigation there by causing a violent current. An inspection of the map of the 
river there will convince all unprejudiced minds that no such evil could result. 
The Canal protection embankment shown by the yellow shade, which the Com- 
missioners partly cut away, must be restored at a cost of £1000, both for the iron 
wall weir and for a movable weir, and then the navigation channel will not be at 
all affected by any current in the river. 
Ido not state that the French “ barrages mobiles,” with their mechanical details, 
are the most suitable pattern of regulating-weir for the Shannon. All I advocate 
is, a regulating-weir either wholly movable or so far movable that when fully open 
it will occupy a head of water in high floods of no more than 3 inches. Such a 
weir may easily be designed and constructed in lieu of the existing stone wetr- 
mounds in the Shannon without any injury to the navigation, and by their use so 
much more fall will be effective in propelling the stream along the different reaches 
of the river that very little excavation to increase the water-way will be required ; 
and the drainage and the navigation of the Shannon may be improved to the 
fullest extent necessary or desired at a cost of £100,000 less than the estimate on 
which the recent Act of Parliament is founded. 
Determination of the Form of the Dome of Uniform Stress. 
By C. W. Merrirrerp, PRS. 
The author had observed that there was a consideralle simplification in’ the 
