1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



265 



structeil, anJ some only proposed. The heights were from 70 to 130 ft., the 

 minimmn price heing 35/ , and the niaxiiimm SO/, per lineal yard. He further 

 pointed out that high embankments should he avoided, and timber viaducts 

 substituted, as a mere point of economy, even without taking into consider- 

 ation the risk .and danger of slipping in such great masses of earth. In an 

 embankment only 40 ft. high, an occupation bridge for a farm would often 

 cost nearly £1000; it was, therefore, only in crossing a very narrow valley 

 or ravine, M here no bridges under would be called for, and no ma.sonry— 

 except perhaps a culvert of the very smallest dimensions— that very high 

 embankments should be m.ide. Mr. Vigno'es alluded to several such, varymg 

 from 70 to 90 ft. higti. which he had made, and pointed out a terrible failure 

 in one case, althougli in other instances success had followed. In passing 

 through hilly countries and along mountain sides torn by ravines, the intro- 

 duction of the timber-top viaduct, with stone piers, to overcome points of 

 great but partial difilculty, was strongly rrcnmmended, especially as great 

 additional height of viaduct could be given at small expense, and thus 

 excavations on each side saved. 



FKOCSEDINGS OF SCIENTIFIC SOCIETIES. 



ACADEMY OF SCIE>"CES. 



3/ay 30. — The reading of papers connected with the accident on the Versailles 

 Raihcay occupied a great portion of this sitting. One of the most interesting 

 was by M. Francois, an engineer of mines, on the means of preventing the 

 crystallization of iron used in machinery. On the examination of the rup- 

 tured axle of the engine, which was the cause of the calamity on the 8th 

 ult., the conclusion come to was. that the rupture had been caused by this 

 crystallization, the iron being of the best quality, and of a volume more than 

 sufficient for the purpose to which it was appUed. Similar results on other 

 railways have been ascribed to the same cause ; but no person has been 

 successful in the means of preventing the recurrence of accident by an 

 improved mode of manufacturing the iron, and all that coidd be done in the 

 way of precaution was, not to permit iron axles to remain in use for so long 

 a period as to undergo the crystalline change which is so fatal, and of which 

 external appearances give no indication. M. Francois informs us, that, in a 

 long continued series of experiments, be has observed that a magnetic action 

 upon iron when in a state of fusion, will produce the change alluded to, 

 causing the small and closely adhering grains to crystallize into coarse and 

 larger grains, depriving it of its compact character ; and it is inferred that 

 the action of heat upon axles employed in machines, subjected to great 

 Telocity, will produce the same effect. This can only be prevented by di- 

 miaishing the volume of silicate in the iron, by carefully sweating the coal 

 employed in melting, and above all, by the use, in the manufacture of axles, 

 of iron which has already undergone a partial change in its vitreous cha- 

 racter, and which, on being reworked, is much less susceptible of crystalline 

 change than new iron. Another communication on the same subject, by 

 Colonel Aubcrt, was also read. He agrees with JI. Francois as to the cause 

 of the imperfection complained of, but appears to think that the only real 

 precaution is, to change the axles employed in railway locomotives so fre- 

 quently as not to give time for them to undergo the crjstalline change, which 

 is found to be so destructive. Another paper, by Mr. Manby, on the causes 

 of railway accidents, and the means of preventing them, excited much 

 attention. This engineer recommends the use of four-wheeled locomotives, 

 but with some important modifications in the construction of them, both as 

 regards the axles, so as to expose them to an inferior degree of stress than 

 upon the present system, and the frame-work of the wheels, which should, 

 he says, be within the wheels, and immediately under tlje boilers. He also 

 lays down some practical rules for counteracting the lialulity of locomotives 

 to run off the rails, and mentions several facts in support of the correctness 

 of the various portions of his system. 



A paper, by M. Pambour, on the means of checking, or rather equalizing 

 the velocity on railways, by the use of fans, deriving a force of resistance in 

 the precise proportion of the velocity communicated by the impetus of a 

 train, was next read. 



M. Fleurian de Bellevue made a commnnication on the deterioration of 

 stone in bnihlings, which he ascribes to an emanation of acid gas from the 

 earth. He recommends a series of minute, but apparently almost imprac- 

 ticable, chemical experiments in the way of analysis of this emanation. 



A communication was read from M. .Vgassiz, announcing that the King of 

 Prussia has placed at his disposal a sufficient sum of money for him to test, 

 in the glaciers of Aar, the truth of his theorv' respecting the progressive 

 motion of glaciers towarda the adjoining valleys. He is about to pierce an 

 opening downwards from the highest point of the glaciers, aud expresses a 

 conviction that the result will prove his theory to lie correct. 



M. Arago addressed the Academy at some length on the eclipse of the 

 sun, then about to take place. 



June 6. — A paper On the nature of the air which «■« breathe, under varioux 

 circumstances, was read. The author, M. Leblanc, has directed his attention 

 principally to an analysis of the air in rooms, hospitals, &c., — in fact, in all 

 situations' wherever it is vitiated by the congregation of persons. He begins 

 by showing, tiiat the air of an empty room, the doors and windows of which 

 are not closed, is precisely the same as that out of doors. This is, of course, 

 natural; but he states also that he found the same to be the ease in the 

 closed green-houses of the Jardin des Plantes, a seeming contradiction, which 

 he explains by the absorption by the plants contained in them of the car- 

 bonic acid of the air, and the giving nut again of this air purified by the 

 plants which had absorbed it. But in one of the wards of the hospital of 

 I.a Pitie, the doors and windows having been closed, the quantity of carbotiic 

 gas — that destructive element to human life — was found to be tripled, as 

 compared with what it was before the room was closed, and, in one of the 

 sleeping-rooms of the SaltpetriDre, the quantity of carbonic acid in the morn- 

 ing, the doors and windows having been closed during the night, was eight 

 times greater than in the open air. In the great lecture-room of the Sor-- 

 bonne, after a lecture of an hour and a half, one per cent, of oxygen had dis- 

 appeared, and been replaced by one of carbonic acid. The quantity of car- 

 bonic acid in one of the ecoles d'asile, of Paris, after it had been closed for 

 three hours, whilst the pupils were taking their lessons, was found to be 

 precisely the same as in the experiment at the Saltpetriere. At the Chamber 

 of Deputies, he found the quantity of carbonic acid vary from two to four 

 parts in a thousand. The latter amount approaches the limit at which res- 

 piration becomes oppressive and injurious. In the latter portion of M. Le- 

 blanc's paper, he gives an account of some experiments with air deteriorated 

 bv the burning of charcoal. 



INSTITUTION' OF CIVIL ENGINEERS. 



March 22. — Joshua Field, V.P., in the Chair. 



On- Water Power. 



" Remarks on Machines recipient of Water Power ; more particularly the 

 Turbine of Fonmeyron." By Professor Gordon (Glasgow). 



Notwithstanding the diminished importance of water power since the 

 almost universal application of the steam engine, some situations may still 

 be found, in the mining districts of Cornwall, of Derbyshire, and of Cum- 

 berland, the Highlands of Scotland, and generally in the districts compara- 

 tively destitute of cheap fuel, where it is desirable to render falls of water 

 available. 



The theory of water power, as it now stands, may be announced in general 

 terms thus : " The mechanical effect obtained is equal to that of the moving 

 power employed, minus the half of the vis viva which the water loses on 

 entering the machine, and minus the half of the vis viva which the water 

 possesses when it quits the machine." 



Bernouilli recognized the second cause, and soon after Euler the first. 

 Borda, in his " Memoire sur les Roues Hydrauliques" in 1767, gave the pro- 

 position in precise and general terms ; whence he concluded that to produce 

 its tot.ll mechanical eftect, " the water serving as moving power must be 

 brought on to the wheel with impulse, and quit it without velocity." 



This principle being admitted, the circumstances ue.it to be considered 

 are : The height of fall — the supply of water — and the nature of the wort 

 to be done. 



These positions heing laid down, the author proceeds to examine the relative- 

 efficiency of water wheels of various constructions. 



The undershot wheel acted upon by the velocity of the water when con- 

 fined in a rectilinear course, or when hung freely in a stream : in the former 

 case the efficiency of the machine is equal to 32 per cent, or nearly one- 

 third ; in the latter the ratio is 42 per cent, or about ffhs. 



The breast wheel is gener.illy applied to falls of from 4 to 8 ft. ; in these 

 the efficiency reaches as high as 60 to 65 per cent, of the mechanical effect 

 of the fall of water. The buckets being filled to two-thirds of their capacity 

 their velocity is seldom less than from 7 to 9 ft. per second. 



The consideration of this wheel led Poncelet in 1824-25 to the invention 

 of the " undershot wheel with curved floats," the eiHciency of which has 

 been found equal to from 65 to 75 per cent. The velocity of this may be 

 55 to GO of that of the effluent water — a velocity equal to that due to nearly 

 the whole height of fall ; hence the efficiency becomes " about double that 

 of the ordinary undershot wheel." This wheel has not been much employed 

 in Great F)ritain, although frequently used in France and Germany. 



The overshot wheel is most generally employed in Great Britain for falls 

 IjCyond 10 ft. in height, and some excellent examples occur for work of every 

 description, from rolling iron to spinning silk. Its efficiency averages 66 per 

 cent, but has risen as high as 82 per cent. 



The economical use of water as a moving power varying in particular cases, 

 rendered desirable the discovery of a receiver cajiable of general ap|)licatioB, 

 in all circumstances of height of fall, quantity of water, and .amount of work 

 to be done; and after intense study Fourneyron produced the Twhine, tlie 

 peculiarities of which form the subject of the paper. 



Tlie imperfect horizontal water-wheels which have been used for centaries 

 in the mountain districts of central Europe and in the northern Highlands, 



