766 BEPORT — 1891. 



pressor -when the total horse-power is equally distributed among the cylinders. A 

 similar statement applies to multiple-expansion motors. 



For the purposes of an example designed to show the value of the compound 

 principle, the author has assumed the Paris pressure — namely, six atmospheres 

 absolute — and made allowances for all losses on the scale that Professor Kennedy 

 found them to exist in the present machinery at Paris over a distance of four 

 miles. ^ The efficiency of the system is taken to he the ratio of the indicated 

 horse-power in the motor-cylinders to the indicated horse-power in the steam- 

 cylinders of the compressor. The following are typical results : — 



Efficiency 

 per Cent. 

 Simple compressor and simple motor ...... 39' 1 



Compound compressor and simple motor 44-9 



Compound compressor and compound motor .... 50-7 



Triple compressor and triple motor ...... 55*3 



8. Sinking Wells and Shafts. By Henkt Davet, M.Inst. G.E. 



In 1881 the President of this Section, Mr. Forster Brown, read a paper before 

 the Institution of Civil Engineers on ' Deep Mining of Coal in South Wales.' 



In that paper the author pointed out the great diificulty and expense attend- 

 ing the sinking of shafts through water-bearing strata, and suggested that a 

 boring might be put down in advance of the sinking into which a pump might be 

 placed to facilitate the operation of sinking. The water being pumped down in 

 the boring below the bottom of the shaft the sinking would be done in dry ground, 

 and would go on without intermission. 



The suggestion appeared to be a valuable one. 



In sinking shafts and wells through water-bearing strata, on time-honoured 

 methods, there is not only the great cost, but, what is often more serious, the great 

 length of time taken in doing the work. A single well for town water supply often 

 takes two or three years or more to execute. 



The subject is of considerable local importance, because of its bearing on the 

 sinking of mining shafts, and it is on that account that the author ventured to 

 bring it briefly before the Section. 



The problem is simply that of keeping down the water in water-bearing strata 

 in advance of the sinking operations, so that the excavation of the shaft or well 

 shall be done in dry ground. 



The ordinary method of shaft or well sinking is to sling a pump or pumps in 

 the shaft and to lower the pumps from time to time as tlie sinking continues ; 

 obviously the excavation has to be performed in water, and if the quantity of water 

 to be dealt with is very great, a large portion of the work has to be done by the 

 men working in a depth of two or three feet of water. 



To facilitate the work, and to reduce the water in which the men have to work, 

 a sump is made under the suction pipe of the pump, and it is the keeping this 

 sump excavated in advance of the other work which is most difficult and tedious. 

 Then there is the delay occasioned by the lowering of the pumps, and providing 

 the appliances necessary to the operation. 



In the plan now proposed, the pump would be placed in a borehole made be- 

 fore the commencement of the sinking of the shaft. The only novelty in the pump 

 is that of adapting it to the purpose. 



It is necessary that debris shall not go down the borehole in quantity sufficient 

 to choke it up. That is provided against by means of a heavy taper shield of cast 

 steel surrounding the pump and resting on the edge of the borehole. This shield 

 is perforated with holes inclined upwards towards the pump to allow water to get 

 into the bf>rehoIe, but to exclude d<?bris. The shield is made very heavy, and by 

 its own weight follows the excavation around the pimip, and also protects it from 

 injury through the blasting of the rock. The pump is made without a foot-valve, 

 the rod of the bucket working through the seating of a valve which rests on the 



.• See British Association Rejjorts, Newcastle, 1889. 



