112 REPORT— 1842. 



deepest part, and the head of water at the highest tides is nearly 36 feet, and only 

 12 at the lowest tides. 



The shield consists of 12 frames wholly independent of each other : each frame is 

 divided in three stories, thus 36 cells are provided for as many miners in front of the 

 excavation, and for a proportionate number of bricklayers who are to form the 

 structure at the back. The exterior part of the shield at the sides and top is covered 

 with cast-iron sliding plates ; and the front, viz. the whole face of the excavation, is 

 covered with small boards (42 in the face of each cell), consequently 540 upon the 

 whole : these are kept pressed against the ground by means of 1080 small screws, 

 which admit of being abutted against the front of each frame. 



The frames at the back are made to bear against the structure by the interposition 

 and agency of powerful abutment screws resting against capacious plates. 



The frames stand upon legs resting upon capacious shoes; and as an auxiliary 

 way, the frames have arms by which each frame may relieve itself upon its neighbour. 



The body of the tunnel consists of a substantial square brick structure with two 

 arches. This structure fills the excavated area, and in this way all the mass of the 

 surrounding ground remains undisturbed. 



The greatest attention, therefore, is to keep and to maintain the abutting screws in 

 their respective functions, not only to support the surrounding pressure, but to pre- 

 vent the ground becoming soft for want of resistance. 



Sir M. 1. Brunei having so far explained his plan of proceeding, concluded by de- 

 claring that the tunnel was accomplished in the manner represented in the drawing and 

 model exhibited. 



On the Use of Beton and Concrete in constructing Breakivaters. 

 By Prof. Vignoles. 



The use of beton had greatly increased in France of late, especially in marine 

 works ; it was similar to concrete, but not exactly identical with it. Beton, like 

 concrete, was composed of lime mixed with broken stones, gravel and sand ; but it 

 required hydraulic lime, while concrete in this country was frequently made of 

 common lime when not to be exposed to the action of water. Beton was first in- 

 troduced in France by Belidor, and lately much advocated by Vicat ; since then 

 it had been much used, and he considered that attention was due to the use that 

 had lately been made of it in the Port of Algiers by M. Poirel, the engineer of that 

 harbour. 



On tJie Construction of a Neio Rope employed as a Core in the formation of 



the Patent Stoppers, a Substitute for Corks and Bungs. i?y William 



Brockedon, F.R.S., Sfc. 



The patent substitute for corks and bungs is obtained by employing an elastic core 

 of fibrous materials of the form required, and covering it with a thin sheet of India 

 rubber. By this combination the tendency of India rubber to harden in these high 

 latitudes is overcome by the elasticity of the fibrous core, whilst the core is preserved 

 elastic by the impermeable quality of the India rubber with which it is covered. 

 But the matter which was more immediately offered to the attention of the Section, is 

 the important improvement which the invention has received by the adoption of cot- 

 ton cores, mechanicallv constructed, as a substitute for the felted wool which was 

 originally used ; by this improvement greater strength is obtained to resist the hold 

 taken by the entanglement of the cork-screw, and greater precision in roundness and 

 accuracy in size; with these come a train of consequent advantages and facilities in 

 the processes of manufacture, which will now be described. But a very short sketch 

 of the invention itself, prior to these improvements, is necessary. 



The idea of such a substitute for cork for stopping bottles and other vessels was 

 suggested to the patentee by Humboldt's researches in South America, wherein he 

 states that the Indians were accustomed to employ plugs made of India rubber for 

 stopping their vessels. The then recent importation of India rubber in large quan- 

 tities by Messrs. Enderby, and the price at which it could be obtained, suggested to 

 the patentee the idea, that if he could cut cores out of the solid blocks he should ob- 

 tain a valuable stopper for decanters ; he knew enough of India rubber to be certain 



