1841.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



389 



MR. BROOKS IN REPLY TO MR. BARRET ON BARS OF 

 RIVERS. 



Sir — In reference to the letter by Mr. Barrett in yonr July number, 

 I shnll merely notice the statements that gentleman makes in defence 

 of his own theory, and this for brevity's sake only, else I should seek 

 to refute the false positions and strained unfair inferences with which 

 the whole is filled. I purpose, therefore, to confine myself to the dis- 

 jiroval of his theory and not aUow him "to go ort' upon another tack," 

 as he seems inclined to do by a statement which contains no notice of 

 his much talked of theory, which is as follows: "The cause of the 

 existence of bars is the conflicting action of effluent currents or tides, 

 passing into tlie ocean al right angles to the shore ;" and he adds as 

 his reimnlv for the removal of the bar, " But if the current or tide be 

 hv artificial means conducted into the ocean so as to join the sea tide 

 n't ail acute angle, no conflicting action can arise, and then no bar will 

 accumulate." On the above I have stated, in page 5 of my Treatise 

 on Rivers, " That the casual direction of the lower reach, or position 

 of the mouth of a river, caimot be truly assigned as the cause of the 

 existence of bars, is easily proved by observations on rivers subject to 

 great variations at their entrances; the bar being always found to 

 exist quite independent of the direction of the discharge into the sea. 

 This fact at once refutes the third and fourth theories which have 

 been noticed above." In the preceding, the words " independent of the 

 direction of the discharge " mean evidently independent of " the great 

 variations" or "casual direction of the lower reach before alluded to; 

 but Mr. Barrett in reply states " In this extract there seems to be two 

 distinct facts, i.e. the casual direction of the lower reach, and the in- 

 dependence of a bar, in the direction of the discharged waters ; that 

 is, he means that the deposit or bar does not occur in the direction of 

 the egress waters. With respect to Mr. B.'s assertion of the inde- 

 pendence of the bar of the egress waters, I have much to say, if he be 

 correct, he has indeed " at once refuted my theory." 



I submit to the judgment of your readers whether the language 

 quoted from my work, which, be it remembered, is in direct reference 

 to the theory by Mr. Barrett, which bases the existence of bars upon 

 the casual direction of the discharge, can by any fairness be construed 

 into the meaning attempted to be put upon it by Mr. Barrett to cover 

 his own want of arguments, or facts in support of his tlieory ? I have 

 not made any "assertion of the independence of the bar of the egress 

 ■water," the plain meaning of my language to any common understand- 

 ing is, that whether the discharge into the sea be effected at either a 

 right, or at an acute angle with the shore, the former case, or a rect- 

 angular direction of the discharge, will not cause the formation of a 

 bar: and the latter, or where the direction of the discharge makes an 

 acute angle with the shore, will not prevent the formation of a bar, 

 or have any effect upon its removal ; and therefore I am correct in 

 stating that the existence or non-existence of a bar is independent of 

 ihe casual direction of the discharge. It is disingenuous in Mr. Barrett 

 to try to make me appear to have said "that the deposit or bar does 

 not occur in the direction of the egress waters," inasmuch as my reply 

 to his theory plainly states that whatever be the casual variation of 

 the direction of the discharge, the bar will still be found attached to 

 it ; whereas, according to Mr. Barrett's theory, tlie bar ought to dis- 

 appear by a certain change of direction of the discharge. The whole 

 of Mr. Barrett's long lectures on bars maybe included in the simple 

 statement that he beheves that a bar is caused by the discharge of a 

 river taking place in a direction at right angles to the line of shore, 

 and that there will be no bar when the discharge takes place in a di- 

 rection w'l}ich forms an acute angle with the shore. These are his 

 assertions, which, however, he does not support by a single practical 

 example. 



Mr. Barrett's theory on the cause of bars rests solely upon the di- 

 rection of the discharge, and I submit to your readers' judgment 

 whether I have, or have not, sufficiently refuted it by showing that 

 bars are as frequently found at the mouths of rivers which discharge 

 their waters at acute angles with the shore, as at the mouths of those 

 ■which are discharged in a rectangular direction. In illustration of this 

 statement, even the youngest of your readers will bring forward many 

 examples. It is, however, Jlr. Barrett's duty to support his state- 

 ment by bringing forward a mass of examples of rivers, which are ob- 

 structed by bars because of the rectangular direction of their discharge, 

 and of otbers which are from bars because of their discharge being 

 effected at an acute angle with the shore. In doing this, of course 

 Mr. Barrett will not omit to notice those rivers which are free from 

 bars, notwithstanding their rectangular direction of discharge, nor 

 will he omit those numerous rivers which have bars, notwithstanding 

 their discharge is at an acute angle ; if he do omit to notice them, I 

 promise to amply supply his deficiency. In Mr. Barrett's last letter 



I looked for practical examples to illustrate his theory on the bars of 

 rivers, the matter in dispute! and in lieu I find advanced as proofs of 

 his accuracy, " the Bay of Wangarver, New Zealand ; " and " the Bays 

 of Plenby and Port Nicholson" as "free from bars"; Mr. Barrett 

 might just as apnropriately have referred to the Bay of Fundy or the 

 Baltic Sea. This same letter contains specimens of the powers of 

 observation and of "the devotion" of which Mr. Barrett boasts go 

 much ; and I might also add, that it contains specimens of his taste 

 where, writing of the " Neva, Gulf of Finland, Narva, Dantzic, 

 Danube, Nile, he adds, "no salt water being in the ricinity of the dis- 

 emboguing site of the above rivers," and he also adds, " that there is an 

 absence of sloping to those rivers." By Narva and Danlzic, Mr- 

 Barrett doubtless meant to have alluded to the Rivers Narova and 

 Vistula ; but wliat does Mr. Barrett mean in another part of his letter 

 where he writes " Norway, Scotland, Ireland, Scilly Islands, MinorcSi 

 and Malta Harbours are of the first kind V 



I am your obedient servant, 

 Slocf:ton-on-Tees, W. A. Brooks. 



12M July. 



RULES FOR CALCULATING THE HORSE POWER OF 

 STEAM ENGINES. 



Sir — The rules for calculating the horse power of steam engines in 

 the Clyde have long been known to be different from those employed 

 by the English manufacturers, and it appears to me that the charge 

 against Mr. Scott Russell's assertions, made in page 312, in the Sep- 

 tember number of the C. E. and A. Journal, is based in some degree 

 on the unsound foundation of this difference. 



The English rule for a cylinder 48 inches in diameter would be 

 founded on two assumptions, the first, that the speed of the piston 

 would be 220 feet per minute, and the second, that the surplus pres- 

 sure on the piston would be 7; or "-l, or 7-3 ft, per square inch. The 

 practice, I believe, varies within these limits, hence 



48-X-7854X220X 7-1 „„ , 



„ .^ = 90 horse power. 



33,000 ^ 



The Scotch rule takes the actual speed of the piston per minute, 

 and the mean pressure per square inch, and then employs 44,000 tt>. as 

 the divisor on the gross, instead of 33,000 tb. on the nett or surplus 

 power of the steam. 



The effect of this rule is an allowance of 25 per cent, of the gross 

 power for engine resistances and friction. 



Under the given conditions — ..„_,' — = lOz 16. is the surplus 

 ° 44,000 *^ 



steam pressure taken, instead of 7-1 ft. the assumed pressure by the 

 English rule. 



If a question had arisen, which rule is preferable, that adopted in 

 the Clyde is, I conceive, superior in every point, especially in the 

 closer approximation given of the real engine resistances. 



W^e have however to deal with Mr. Scott Russell's assertions; that 

 the Flambeau, built on the wave principle, " with the smallest propor- 

 tion of power to tonnage, and smallest supply of steam, is never- 

 theless the swiftest vessel on the Clyde." 



The assertion of greatest speed obviously referred to last seasotj, 

 and is granted to be correct. The least steam assertion is in fact 

 granted by the account of the change of the boiler, but the effect of a 

 new and probably heavier boiler is curious, and an accurate state- 

 ment of the facts would be valuable. Ou the estimate of horse power 



260 

 here given, as the Flambeau is 280 tons, we have -— -:=3 tons per 



horse power. 



Is the assertion of less po'wer in proportion to tonnage correct or 

 not, on this estimate? (Clyde boats are notorious for power in pro- 

 portion to tonnage, an opinion due I conceive to the rule of horse 

 power used on that riverj — other boats of course being estimated in the 

 same mode — however I should prefer a comparative estimate of both 

 by the Clyde rules ; and it would be extremely interesting, if accom- 

 panied by the dimensions of the steam boats, and of their engines, 

 with other particulars ; for though the public may but slightly regard 

 questions relating to Mr. Scott Russell's figures, yet the success or 

 failure of the Wave principle applied to ship building will and ought 

 to command attention, provided satisfactory data can be supplied. 



However desirable an uniform method of calculating horse power 

 may be, yet its general adoption will be prevented, by the wish of 

 each party to impose their own rule on others ; but the fact of an ex- 



3 F 



