140 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[April, 



diameter to enable them to excavate lateral galleries, but they had sunk 

 their well in the Hampstead Road, of a small diameter, as described in the 

 paper by Mr. R. W. Mylne, published in the third volume of the transactions 

 of the Insttuition ; ' and although fissures had fortunately been traversed, 

 which gave an ample supply of water, many of the difficulties encountered 

 would, he contended, have been avoided by adopting the larger diameter, 

 and sinking the cylinders into the chalk, before the pumping was com- 

 menced. 



The supply of water at Messrs. Reid's well had been sensibly affected by 

 the recent proceedings at the Hampstead Road well, which was now being 

 constantly pumped in order to sink it deeper. 



Mr. Davison explained that a bore of small diameter had been adopted, 

 because it was calculated that a supply of water, sufficient for the wants of 

 the brewery, would have been obtained by it. The excavation to within five 

 fec-t of the chalk was suggested by the sudden dropping of the cylinder. He 

 believed that when (contrary to his express instructions) the level of the water 

 was reduced by pumping to below a given point, the sand from beneath the 

 oyster-bed rushed in to restore the equilibrium within the cylinder, and thus 

 caused the difficulties which he had to contend with. 



During the last year the pumps had been at work 1616 hours, in which 

 time 300,000 barrels, or 50.000 tons, of water had been drawn from the 

 well. 



Mr. Farey believed that the casualties in well sinking, generally arose 

 from the sources which had been mentioned. Mr. Voolf encountered them 

 when sinking the well at Messrs. Meux' (now Messrs. Reid's) brewery. The 

 pumping up of sand with the water was there carried to such an extent as to 

 cause an accumulation of sediment two feet deep in the liquor back, in 11 

 days, and ultimately the new well broke into the old one adjoining it. 



Mr. Braithwaite explained, that, in the year 1814, the well at Messrs. 

 Meux was pumped " to clear the spring," which caused a cavity of nearly 40 

 feet deep from the sides of the well, and endangered the stability of the 

 buildings around. Piles were therefore driven to support the upper ground, 

 and upon them the brick steining was carried up. If the cylinders had in 

 the first instance been carried down to the chalk, before the pumping had 

 commenced, this accident would not have occurred. 



Mr. Vignoles remarked that the same question, as to the relative merits of 

 boring or sinking, bad been discussed at Liverpool, for wells in the red 

 sandstone, and in practice it had universally been found that, by the latter 

 system, the best supply of water had been procured, particularly when side 

 drifts had been made. 



Mr. Mylne said that the works at the well in the Hampstead Road, which 

 had been repeatedly stopped from accident, were now resumed as an experi- 

 ment ; the quantity of water obtained was more than could be drawn by a 

 pump 12 inches diameter, 6 feet stroke, making 10 strokes per minute 

 (=: 204 gallons per minute). The spring was struck at about 234 feet 

 below the surface of the ground, and when the engine was regularly at work, 

 the water generally stood at within 20 feet from the bottom of the well. 

 He coincided in the opinion of the advantage of a well of large diameter 

 over one of small bore, as it permitted side excavations to be made in search 

 of water. This plan had been pursued with success at Brighton. 



Mr. Taylor observed that another of the advantages of the large diameter 

 was, that the proceedings could be watched, and accidents could be more 

 readily remedied ; the opinion of all practical miners was, that the large 

 diameter was cheaper, as well as better, than the small bore. 



Mr. Clark promised an account and drawings of a well now sinking by 

 him at the Royal Mint. The advantages of a large diameter were manifest 

 to all practical men, particularly when the augur or " miser " was used, as it 

 enaliled the operation to be continued without pumping; the cylinder, in 

 lengths of not more than 30 feel each, followed the "miser" down regu- 

 brly, and as soon as they reached the chalk, the operation was considered 

 sale; and as the " miser" did not excavate more than was due to the area 

 of the cylinder, the equilibrium between the water within and the sand 

 without the cylinder was never disturbed. In a well sunk by him at Messrs. 

 Watney's distillery, the cylinders were 11 feet diameter; the "miser" used 

 was 5 feet diameter, and was turned by twelve men at a time. 



Mr. Braithwaite concurred in the advantages of using the "miser;" he 

 invariably employed it, and generally with success. 



Mr. Farey believed that the augur or "miser" was first used in this 

 country by the late Mr. Vulliamy,- of Pall Mall, for sinking an Artesian 

 well, into which there was an irruption or blow of sand, the effect of which 

 was onlv overcome by this instrument. 



" An Experimental Inquiry as to the Co-efficient of Labouring Force in 

 Overshot Water-wheels, whose diameter is equal to, or exceeds, the total 

 descent due to the fall ; and of Water-wheels moving in circular Channels." 

 By Robert Mallett, M. Inst. C. E. 



This paper is partly mathematical, and partly experimental. The investi- 

 gation which it details, the results of which are given in ten tables of experi- 



1 Trans. Inst. C. E., vol. hi. p. 229. 



2 Vide Nicholson's Journal of Philosophy, vol. li. p. 266,— •' An Account of 

 the means employed to obtain an Overflowing Well at Norland House in 

 1794," by Benjamin Vulliamy. 



ments, had in view principally to obtain the definite solution of the following 

 questions. 



1st. With a given height of fall and head of water, or in other words, a 

 given descent and depth of water in the pentrough, will any diameter of 

 wheel greater than that of the fall give an increase of labouring force (;'. e. a 

 better effect than the latter), or will a loss of labouring force result by so 

 increasing the diameter ? 



2nd. When the head of water is necessarily variable, under what con- 

 ditions will an advantage be obtained by the use of the larger wheel, and 

 what will be the maximum advantage ? 



3rd. Is any increase of labouring force obtained, by causing the loaded arc 

 of an overshot wheel to revolve in a closely fitting circular race, or conduit ? 

 and if so, what is the amount of advantage, and what the conditions for 

 maximum effect ? 



The author briefly touches upon the accepted theory of water wheels, the 

 experimental researches of Smeaton, and the recent improvements in theory, 

 due to the analytic investigations of German and French engineers. 



Smeaton, in his paper on water wheels, read to the Royal Society in May, 

 1759, and Dr. Robison, in his treatise on water wheels, iay down as a fixed 

 principle, that no advantage can be obtained by making tlie diameter of an 

 overshot wheel greater than that of the total descent, minus so much as is 

 requisite to give the water, on reaching the wheel, its proper velocity. 



The author, however, contends that while the reasoning of the latter is 

 inconclusive, there are some circumstances which are necessarily in favour of 

 the larger wheel, and that conditions may occur in practice, in which it is 

 desirable to use the larger wheel, even at some sacrifice of power ; and that 

 hence it is important to ascertain its co-efficient of labouring force, as com- 

 pared with that of the size assigned by Smeaton for maximum effect. 



The author states, first, the general proposition, " that the labouring force 

 (" travail " of French writers), or " mechanical power" of Smeaton, of any 

 machine for transferring the motive power of water " is equal to that of the 

 whole moving power employed — minus the half of the vis riva lost by the 

 water ou entering the machine, and minus the half of the vis viva due to the 

 velocity of the water on quitting it." He deduces from the theory, the 

 following results, coinciding with the conclusions obtained by experiment. 



1st. If the portion of the total descent passed through by the water before 

 it reaches the wheel be giveu, the velocity of the circumference should be 

 one-half that due to this height. 



2nd. If the velocity of the circumference be given, the water must descend 

 through such a fraction of the whole fall before reaching the wheel, as will 

 generate the above velocity. 



3rd. The maximum of labouring force is greater, as the velocity of the 

 wheel is less j and its limit theoreticallv approaches that due to the whole 

 fall. 



General equations are given, expressing the amount of labouring force in 

 all the conditions considered, and their maxima. 



One of the principal advantages of using an overshot wheel greater in 

 diameter than the height of the fall, is the power thus afforded, of rendering 

 available any additional head of water occurring at intervals, from freshes or 

 other causes, by admitting the water upon the wheel at higher levels. 



The first course of experiments is dedicated to the determination of the 

 comparative value of two water wheels, one of whose diameter is equal to 

 the whole fall, and the other to the head and fall, or to the total descent ; 

 by the head, being in every case understood, the efficient head, or that due 

 to the real velocity of efflux at the shuttle, as determined according to Smea- 

 ton's mode of experimenting. 



The apparatus employed in tlus research consisted of two accurately made 

 models of overshot wheels, with curved buckets. These were made of tin 

 plate, the arms being of brass, and the axles of cast iron. Special contri- 

 vances were adopted to measure the weight of water which passed through 

 either wheel during each experiment, to preserve the head of water strictly 

 constant, and to determine the number of revolutions, and the speed of the 

 wheels. 



One wheel was 25 - 5 inches diameter, the other, 33 inches diameter. The 

 value of the labouring force was determined directly, by the elevation of 

 knoun weights to a height, by a silken cord over a pulley; the altitude 

 being read off on a fixed rule placed vertically against a lofty chimney ; and 

 in other experiments, relatively by the speed of rotation given to a regulating 

 fly or vane. The depth of the efficient head was 6 inches in all cases. 



The weight of water passed through either wheel in one experiment, was 

 always 1000 pounds avoirdupoise. 



All the principal results given in the tables accompanying the paper, are 

 the average of five good experiments ; from the large scale upon which these 

 were conducted, the accurate construction of the apparatus, and the care 

 bestowed upon the research, which was undertaken with reference to an 

 actual case in the author's professional practice, be is disposed to give much 

 confidence to the results. 



The weight of water contained in the loaded arc of each wheel is accu- 

 rately ascertained, and in the tables which accompany the paper, the results 

 of the several experiments are given at length. 



The velocity of the wheels, under different circumstances, is carefully 

 noted and discussed with respect to the maximum force. 



The author next ascertains the value of the circular conduits, and states 

 that generally, in round numbers, there is an economy of labouring force, 

 amounting to from S to 1 1 per cent, of the power of the fall, obtained by 

 the use of a conduit to retain the water in the lower part of the buckets of 



