1843.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



si 



brine-pump. This is no supposition on our part ; it is a practical fact 

 well known to most marine engineers. 



The result given by us is also a minimum, inasmuch as we have only 

 considered the txact quantities of steam required, and have not made 

 allowance either for condensation, or for the waste at top and bottom 

 of the cylinders, preferring that our readers should estimate this 

 according to their own views, as far as our experience goes, we believe 

 the allowance ought to be about jfc of the whole quantity. 



But has Mr. Envs any reason to conclude that these engines are to 

 be worked expansively ("we of course assume that he is not in any way 

 connected with the undertaking) ? We think not; and that such is 

 not the intention of the engineers. We have noticed that she is 

 fitted with ordinary sliding valves, arranged (with a lap of 2J inches, 

 and stroke of 14 inches) to cut off the steam at | of the stroke, we 

 suspect that the separate expanding apparatus is to be used in 

 fine weather, as in most steamers of large class; and it will be 

 observed that Mr. R. Hill expressly states that the cranks are placed 

 in opposite directions, and not at right angles (p. 254) ; and, further, 

 the construction of the boiler is proof that the engines are occa- 

 sionally intended to exert their full power, say an average pressure on 

 the piston of 141b. per square inch. 



We are inclined to be thus particular with reference to this point, 

 because our professional knowledge has been questioned, in having 

 made the statement that the grate surface is "less than half the 

 proper quantity." We are, however, hardy enough to reiterate this 

 assertion ; and further to say (if any dependence is to be placed on 

 the drawings), that a more unscientific or badly arranged boiler could 

 not be devised. We have made a careful analysis of its properties, 

 and it bears out our views that it is constructed (by the amount of its 

 absorbent surface) to supply steam for the full power of the engines, 

 at which the consumption of coals will be fully equal to our original 

 computation, namely, 129 tons per day. It is as follows : 



Fire surface of the six boilers = 2220 square feet. 

 Flue surface do. =11870 do. 



Total surface 14,090 



(f the total surface be divided by the total horse power, we shall 

 have 14090 -7- 1176 = 12 square feet per horse, and the grate surface 

 2 feet X 6 x 24, = 288, -7- 1176 = -245 of a square foot per horse ! 



We have no disposition to cavil about words, but think we may 

 call the practice of our first engineers proper, but certainly not usual, 

 in as much that in this very case there is an exception to the rule, and 

 a straining after novelties at the expence of that which is useful. We 

 here find that we have more than the proper quantity of absorbent 

 surface, and less than one half the grate surface, and the result will be 

 a very indifferent ratio of evaporation, as will be discovered when it 

 is too late. 



The size of the air-pump must of course be large enough to suit the 

 extreme power of the cylinders, and cannot be adapted to various 

 grades of expansion. With respect to the large condensers, theory 

 taught us the doctrine as that propounded by Mr. Enys — the larger the 

 better; but, from actual observations and practice, we find it is 

 not correct, and that Mr. Watt was right in constructing his con- 

 densers of the same capacity as his air-pump. The proportion of 

 Mr. Watt for his air-pump is about a sixth of his cylinder contents; 

 and it is reasonable and just, the steam rushing from the cylinder, is 

 condensed in detail, and the air-pump, at owe stroke, clears the con- 

 denser of whatever vapour may remain. In the Great Britain this 

 vapour will accumulate in the condenser; being between 7 and 8 times 

 larger than the pump, which has no power to clear it; the condenser 

 becomes hot, and no extreme quantity of injection water will keep it 

 cool. We may or may not be correct in our view of this matter, but 

 practice supports it, as our readers will see by reference to our last 

 December number, page 399, vol. V., in which we have detailed the 

 proportions used by some of our most eminent engineers. 



We have little more to say regarding the probable speed of the 

 Great Britain. We believe the factor 1400 to be applicable, having 

 found it correct in very large vessels ; and we see nothing in the con- 



struction of the Great Britain to render it inapplicable; presuming 

 that the resistance (in all cases of similar form, as it regards the 

 sharpness of the water lines) is very nearly as the areas of the im- 

 mersed midship sections; lengthened experience and experiments 

 with a great number of vessels have proved this. In this case our data 

 is meagre, and we have no desire to carry the subject further, espe- 

 cially as it is probable that an actual trial of the Great Britain will 

 soon settle all the questions in dispute. 



We close with the remark, that however we dissent from the views 

 of her engineers in matters of detail, we most sincerely hope that we 

 may be found false prophets, and that the Great Britain will prove 

 to be superior, if possible, to her sister vessel the Great Western, and 

 that the proprietors will have every reason to be proud of their 

 speculation. 



THEORY OF ARTESIAN WELLS. 



A French pamphlet, from which the following translation is made, 

 has excited considerable interest in France, and is, up to this time, in 

 constant requisition by the numerous visitors to the scene of M. Mulot's 

 labours at Grenelle. Our readers, however, will have the goodness to 

 observe, that although we present it to their notice, partly on account 

 of the notoriety which the author's views have obtained in France 

 and partly because it is important to consider ingenious arguments on 

 both sides of a question like this, at the same time we feel bound to 

 dissent almost entirely from the author's explanation. 



If the ingenious and eloquent Parisian had been favoured by pre- 

 vious acquaintance with the phenomena of springs as exhibited in the 

 extensive mining operations of this country, it is probable that his 

 surprise would not have been so mightily excited by the Artesian 

 fountain at Grenelle, and he might possibly have entertained a diffe- 

 rent and more generally received opinion as to its origin. 



A grand Experiment; or the Well at the Abattoirs of Grenelle. 



C'HAFrER I. 



Exposition of the Subject ; false attempts at Explanation. 



This work which has discovered to the city of Paris the source of an abun- 

 dant supply of water, has been not more remarkable for the boldness of the 

 conception which gave rise to it. than for the perseverance with which the 

 design has been followed out. In the bosom of the capital M. Mulot has 

 opened a sort of aqueous mine, rich and magnificent ; and for this great 

 boon the Parisians are unanimous in their expressions of admiration and 

 gratitude. The sight of the ascending stream rushing upwards from so great 

 a depth beneath the surface has daily attracted crowds of visitors. After 

 the first gratification of their curiosity, the attention of this multitude is 

 naturally directed to the cause of so extraordinary a phenomenon, and the 

 desire for information on the subject corresponds with the admiration it 

 excites. Each successive visitor asks himself, or inquires ot those are ind 

 him, whence can proceed so impetuous a stream ? what force impels it ? w hat 

 immense reservoir feeds it? in what part of the earth is deposited this fruitful 

 supply, and by what passages and communications does it find access to the 

 extremity of the vertical tube which M. Mulot has forced into the bowels of 

 the earth? The scientific men of the present generation have endeavoure.1 

 to answer these questions. Referring to the very simple means which human 

 ingenuity has long since employed for embellishing our gardens and publio 

 places with jets of water, they have said,— At a certain distance from Paris, 

 and in the upper stratifications of a soil mure elevated than Paris itself, there 

 exist vast reservoirs fed by the infiltration of rain water and of melted snow. 

 This water there sinks to great depths below the surface, aid. Bowing in 

 subterranean sheets, the augur ol the engineer discovers it M a spot 

 far distant from where the earth fust received it, and after he has thus suc- 

 ceeded in boring down to it, the liquid element naturally ascends to the sur- 

 face through the vertical issue which he prepares for it. This is then a real 

 jet d'eau. Nature has placed the first, that is, the descending branch ; the 

 engineer places the second, the ascending branch; the machine is perfect. 



11* 



