TRANSACTIONS OF THE SECTIONS. 245 



are 7 ft. by 4 ft. 6 in. culverts, havings brick arches and inverts and aslibir sides. 

 About 60,000 cubic yards of masonry lia^e been put into the lock, a quantity that 

 represents about 100,000 tons of stone. The stone used in the works is of various 

 kinds, according to the situations and uses in and for which it is applied. The dock 

 walls are 20 ft. thick at the bottom, and gradually reduced to 7 ft. thick at the top. 

 They have a curved batter on the inner face on a radius of 157 ft. The lower 

 foundation is of blue lias concrete, and over it Portland concrete to 2 feet below 

 the iloor of the dock, where the masonry commences. The dock-gates, originally 

 intended to be of iron, consist of oak keel and mitre-posts and cross pieces of pitch 

 pine. The lower gates are designed to retain a 41i-ft. head of water. On the rib 

 next the sill the pressure of the water is about I5 ton per square foot, and tlie total 

 stress resulting on the sectional area of the rib is 77'3 tons. The leaf is 3 ft. thick 

 at the centre, and 2 ft. 8 in. at keel and mitre-posts, so that the effective sectional 

 area of the rib is 384 square inches, and the stress on the square inch about one 

 fifth of a ton. The total weight of one leaf of the lower gate is eighty nine tons. 

 There has been a double line of railway constructed, at the joint expense of tho 

 (Jreat Western and Midland Railway Companies, to connect the dock with the 

 respective .systems of those Companies, and that will bring the dock into commu- 

 nication with all parts of England. 



On Chrome Steel. By Col. Careington, U.S.A., LL.D. 



On Sharpness Doclcs. By W. B. Clegkam, CE. 



On Toughened Glass. By J. D, Cogak. 



On a Si/stem of Audible Signals for Bailivays. By Messrs. Ceicdton & Ceaig. 



The object of this invention is to prevent a class of accidents of very frequent 

 occurrence, viz. those that arise from non-observance of signals. The desired end is 

 attained by self-acting apparatus, causing the engine whistle to soimd when a driver 

 inadvertently passes a danger-signal. 



The inventors have foimd that the following qualities are essential to apparatus 

 for this purpose, and they trust it may be found that they have been successful in 

 embodying the same in the system described : — 



1. The impact of apparatus fixed on the line against that upon the engine must 

 not cause injm-y to either. 



2. Special provision must be made to counteract the tendency to carelessness that 

 usually results from the employment of automatic machinery- 



3. The apparatus should be constructed so that it cannot be kept out of action 

 either through negligence or improper motive. 



4. It should be solely auxiliary, and in no way a substitute for the appliances at 

 present used in securing safety. 



5. It should be capable of being adapted to the vai'ious types of engine. 



6. The apparatus on the line should be easily actuated and not liable to derange- 

 ment from contingencies of weather. 



7. The whole should be of simple construction and thoroughly reliable in action. 

 Description. — At each distant signal a simple piece of mechanism is placed beside 



the line of rails. It may be described as a bell-crank connected by a wire to said 

 signal, so that both work in unison, i. e. an arm of the bell-crank moves towards the 

 rails at the same time that the semaphore arm rises to danger, and recedes when 

 the semaphore arm falls. 



The engine carries a vertical rod, which is free to slide in a protecting tube attached 

 to the side of the " cab." This rod is connected at its tipper end to a lever, which 

 acts upon an arrangement for sounding the whistle, precisely the same as that now 

 extensively used for the passenger's communication. (The same mechanism may 



