THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



257 



1842.] 



bo in danger of being broken down, or otherwise injured. Few timber 

 stei^ers. he adds, can be placed in the graving dock, without firs 

 s ackenVna the hoUling-down bolts of the eng.nes to allow the vessel 

 spreahut, lest the^framing should be broken. Were iron vessels 

 leiieral, the case would be di&rent ; the engineer might, with perfec 

 irty, firmly unite the vessel and the engine being the de-gn r o 

 both- and being responsible for the success of the whole he will not 

 allow one part to suffer for the benefit of the other, but labour to com- 

 bine both so that they shall mutually support each other. "Then, 

 indeed"" s.ys Mr. Grantham, "we may expect to see a perfect 



'Tconclusion, we feel it our dutv to say that the public ^^re greatlv 

 indebted to Mr. Grantham for having taken up. this subject, and 

 treated it with so much ability. 



The Theoni and Practice of ProijelUng through Water, >r>th observations 

 ontlccinparatn. Resistance offered by IVatcr to Bod,es movmg 

 through it at different Felocities, comprising aho a Description o/ an 

 Imp°oved Method of applying Mechanical Power to Steam Navi- 

 gation. By Hekrv Booth. London : John ^^ eale. 



Mr. Booth is so favourably known to practical men by his past 

 successful exertions in the cause of steam improvement, that any 

 speculations of his, relative to such subjects deserve an attentive con- 

 sideration, and are almost sure to obtain it. The ultimate object of 

 his present pamphlet appears to be the recommenda ion of a p an ot 

 propellino- vessels he has invented, and from which he anticipates far 

 greater efficacv than can be obtained by any modes at present in use ; 

 and lie seems 'to found this anticipation partly upon t be conviction 

 that the received theory of resistance is erroneous, and he calls upon 

 engineers " not quietly" to acciuiesce in the appalling theory which 

 ordains that 30 horse power being required to move a given vessel 

 and burthen 5 miles in the hour, '2-10 horse power will be Kqu-yed t" 

 move the same vessel and burthen 10 miles in the hour. Mr. bootli s 

 conviction of the inaccuracy of the received theory of resistance is 

 founded upon the results of certain experiments which he rela es, ancl 

 which, if correctly conducted, certainly present some anomalies not 

 very easily explicable. In experiments with models for ascertaining 

 their resistance when moving in water, he objects to the use ot a 

 weight moving at very different velocities as the true representative 

 of the amount of power expended. He says, and his assertion is 

 obviously true, that a weight which descends 10 feet in ., seconds 

 does not give out as much power as the same w;eight falling the same 

 distance in (1 seconds, and that at the velocity due to the descent of 

 a body falling freely, no power could possibly be given out; and lie 

 suppo'ses that the apparently great increase of resistance to models 

 moving in water at high velocities, is partly due to the dimimshed 

 efficacv of the weight as a moving power, the velocity of the weight s 

 descent having in many experiments at least been increased with the 

 increased velocity of the model. By making such arrangements m 

 liis apparatus that the time occupied by the weight in descending 

 through a given space was always the same, and the velocity ot the 

 model varied by the use of larger or smaller drums for coiling up tlie 

 string, Mr. Booth has obtained results very dillerent from those ob- 

 tained where the drums remained of the same diameter, and the in- 

 crease of the velocity of the model was attended by an increased 

 rapidity in the descent of the weight. u f ti 



There are several circumstances which prevent the results ot tlie 

 experiments from being conclusive in our eyes. The difierent degrees 

 of the immersion of the models do not appear to have been noted; 

 and the want of uniformity in this respect is an obvious source ot 

 fallacy. At high velocities it is well known models and light boats 

 will rise almost out of the water, and their resistance will then be 

 very little; and whether this source of diminution in the resistance 

 may not have existed in these experiments— or to what extent— we 

 are unable from the details before us to assert. Mr. Booth will pro- 

 bably tell us, that the velocities in the cases from which he has drawn 

 his results were equal, and that therefore the effect proper to the di- 

 minished immersion of the boat must be equal also. But he must 

 recollect that the boat in the one case travelled a greater distance than 

 in the other, and although it is true that 7 ft. G in. of progress in 3 

 seconds is equivalent to 15 ft. in (i seconds, yet the rates of progres- 

 sion are different, and the sum of the resistances may consequently be 

 unequal. In other words, if 15 feet be travelled over in >> seconds, 

 less than half of the 15 feet will be accomplished in the first 3 seconds, 

 and more than half in tlie last 3 seconds, the velocity being accele- 

 rated ; and in the cases where the 15 feet were passed over, there may 



be a diminished resistance in the first part of the motion from its 

 Greater slowness, and in the last part of the motion from the diminished 



''"T^^ZeZZit. of fallacy to which we cannot now advert, 

 and must content ourselves with saying that we do not think any 

 exper me'its upon the resistance of bodies moving in water where the 

 nrim; mover is a weight susceptible of acceleration in .Is descent 

 are nam- degree entiUed to confidence. Major Beauh.y employed 

 a chain he Ihiks of which were raised successively from the ground 

 by the le cending weight, to counteract the tendency to acceleration. 

 Other experimentalists have made use of governors, and other con- 

 tri •ances'for the same purpose, and the resistance has been measured 

 by a dynamometer. All the experiments so conducted have been con- 

 firmatorv of the received theory; and we shall be willing o pu equal 

 fiTh in Mr. Booth's researches so soon as he shal have adopted s.mi- 

 a y efficacious means of obviating error and holds the ™™ersion of 

 his models at the different velocities to be a necessary element of the 



'" BuUt is not upon experiment alone that the received theory rests 

 it« pretensions; running 'water and wind, it is we known, impinge 

 upon stationary objects with a force increasing as the square of the 

 elocity, and the -atmospheric resistance to railway trains fo lows the 

 same la; If water be let into an inclined shoot, the velocity ot the 

 wMer two feet down will be twice what it is at one foot down ; and 

 1?U irthe lame nuantity of water which runs at twice the velocity, 

 ?he dept of water'in the shoot at the lower level will be only one 

 haVof' hat it is at the upper. Now every particle of water which 

 fs two feet will, by virtue of the fundamenta laws of mechanics 

 ha e ust wice the foVce as every one of those which have descended 

 onefio aida particle of water will therefore strike any object at 

 die lower "evel with just twice the force that .t would do at the 

 „»r .m all the Daricles of water in the shoot, if striking against 

 "r/y" w iu g y'e out twice the force at the lower level that they 

 would d^a he upper. But at the lower level they occupy only half 

 he depth in he shoot, and therefore impinge upon only half the area ; 

 a^d a do b d force upon half the area is just a quadrupled force upon 

 the whoTa ea, which is the received theory. Mr. Boo h says a con- 

 id eX part of the resistance of ships s made up of fr.ctioi, and 

 hat friction does not vary as the square of the velocity. To this it 

 on v necessary to say that we know so little about friction that we 

 hokl it unwise t'o draw any analogies from it. Friction, we know, is 

 ncUsed by increasing the rubbing surface, and increased also by 

 minishin^it : it is increased by allowing two pieces o some sub- 

 taices c°ontict to remain for a few minutes at rest, w iilst in other 

 cases no appent increase takes place, and it is certainly aftected by 

 many causes which we cannot hold to be mechanical. Besides, we do 

 ot b'el e"e that friction forms any considerable part of tl.e oppo-tion 

 exoerienced by a vessel in moving through the water. The speed ot 

 as?e"uve elisalways increased, at least in smooth wa er, by in- 

 creasing her length, and in some cases, as Mr. Booth, in another place 

 a seis by increasing the breadth ; but in both of these cases the fric- 

 tion 's increased. Thus much we have found it necessary to say in 

 suppor of the received theory of the resistance being as the square 

 of Ae veloc ty; but whether as the square o the velocity or as any 

 thinc^elsTwe donotthinkittobeat all relevant to the merits of 

 M Bootl I's propellers. Whatever the resistance may be, it is un- 

 changeabh' fixed in the nature of things, and has to be overcome by 

 Mr R^o 1 's uronellers, just as much as by any others. Propel ers niay 

 vmlnexpendin' he engine power more or less beneficially, but they 

 cannot aUei- the ?sistance of the ship, and we are at a oss to discover 

 the leas'm of these two questions having been mingled together in 



''Tli;:S:ur:7;Sulsion Mr. Booth recommends,maybe under- 

 stood by- supposing a double arm upon each side of the ship extending 



f m th'e oXary^position of the P-'f/''"'-, '",;'■;,:;''', ">„,'^td 

 the water level, moved backwards and forwar . b> he engme, am^^ 

 furnished with a plate moveable upon an axis at ib. lo«ei <^Yr''™»y- 

 This arm consists of an inner and outer portion, between which the 

 nhte is situated, and this plate is so hung that upon the advance of 



U from opening or shutting with an injurious force. Mr. bootti also 

 biteiTs Un't i? project sh-.dl be in active operation during only a small 

 port on he sfroke of the engine, the power given out by the engine 

 durnp. the remainirg portion being accumulated by means ot fly 

 M< to ci -e a speed to the propellers during this short interval of 

 •U' miles per hoer. The action proper to a row-boat is hus approx- 

 ma^edto,';nd horses are imitated, 'who, in pulling a boa,, always 



