1819.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



Experiments with Tou^ng, as per the accompanying Table. 



201 



In June 184.1, the African towed the Numa transport of 323 tons, 

 at the rate of 5i statute miles per hour. 



In July following she towed H.M. steam-frigate Dee, of 70+ tons, 



and 200-horse power, 5 statute miles per hour,— which was only 1-6 

 miles per hour less than her greatest speed when propelled by her 

 own engines, or 6-6 miles per hour. 



Woolwich Yard, 1 

 July 9, 184-1. J 



'African; Steam-Tug; Trials of her Towing Qualities with Mr. Rennie's Trapezium Wheels. 



(Tonnage, 323 tons new measurement. Power, 2 x 45 horse engines = 90 horses' power.) 



First Experiment— Towed the 'Numa' Transport from Deptford to Greenwich. 



Second Experiment- 7oi«e<« the 'Dee' Steam-Frigate from Woolwich to Sheerness. 



July 7 



July 8 



No. of 

 Ex- 

 periment. 



Draft of 



Water of 



Tug. 



JF.S 9J-I 

 tA.9 9 / 



Dip. 



ft. in. 

 2 10 



Draft of 

 Vessel 

 Towed. 



fF. 8 9\ 

 1 A. 8 J 



Where tried. 



Barking I 



to 



Sea Reach J 



' Sea Reach "1 



to the I 



Nore ; with I 



2nd motion. J 



^Lower part of] 



Sea Reach I 



to j 



^ Barking. J 



Duration 

 of Ex- 

 periment. 



h. m. 

 2 25 



2 



3 15 



Distance 

 Run. 



Knots. 

 HA 



22, 



Rate 



per Hwur. 



4-4 



4-42 



6-8 



Revolu- 

 tions. 



23 to 24 



34 to 38 



27} to 28 



Remarks. 



r Wind W.S.W.; Deeintovi; mo- 

 \ derate breeze. 



f Strong breeze right aft, which 

 I assisted the Tow materially ; steam 

 \ difficult to keep up at 38 revolu- 

 1 tions ; throttle valves half open ; 

 |^2nd motion in gear, 

 r Fresh breeze ahead and on the 

 J how throughout the run ; 2nd mo- 

 l^tion not in gear. 



The official report only differs by half-a-mile between the towing 

 powers of the African with her rectangular floats in 1837, and the 

 trapezium floats in 1841; so that considering that the area of the 

 trapezium floats was merely adapted to propelling the African 

 simply as regarded speed, these trials could hardly be taken as the 

 criterion of their powers as applied to towing, when the areas 

 should have been increased expressly for that purpose. But, com- 

 paring the whole of the experiments when tried in still water under 

 the most favourable circumstances, and when tried in the African 

 under the unfavourable circumstances of foul-bottom and differ- 

 ence of the powers of the engines, the conclusion is in favour of 



the trapezium floats. The truth of the principle is confirmed by 

 Mr. Ewbank, and by the laws which govern the forms of the tails 

 of fishes, the feet of aquatic birds, and the wings of birds and 

 insects, whereby the means are so admirably suited to the ends; 

 and the triangular form proposed by Mr. Ewbank for paddle-floats 

 entirely confirms the view 1 took of the subject in the years 1S.S9 

 and 1840. 



I remain, &c. 



George Rennib. 



London, August 15, 1849. 



DISCHARGE OF WATER FROM RESERVOIRS. 



The Theory of the Contraction of the Movement of Water flowing 

 from Apertures in thin Plates, in a Reservoir in which the Stirjace 

 of the Water is maintained at a constant altitude. By J. Bayer, 

 Lieutenant. (Translated for this Journal from Crelle s 'Journal 

 fiir die Baukunst.' Band 25.) 



{^Continued from page 246.) 



10. 

 Discharge from Vertical, Elliptical, and Circular Orifices. 

 The equation between the co-ordinates x and y in an ellipse is— 



4ft2 



y^ = a2 C^a^ - X-). 



Substitute this value of y in the equation (H § 9), and there 

 follows — 



26 /* 

 a. q = k V(*») ■ -^y '^-'^ 1/ { (2a.f - «^) (H 4- .r) } . 



; integration of this equation is practicable only in the case 

 H = 0, and the development by series has also difticulties, 



The 



where ^. , , . , ^ tt • re ■ .i 



as no series can be found which for every value of H is sufhcientJy 

 convergent. For this reason, it is necessary to transform the ex- 

 pression. Before proceeding to do this, we may however deter- 

 mine the integral corresponding^'o the value H = 0. In this 

 case the equation (a) becomes 



6. 



Q = k\/Hg) .^ /^rd.v^{2a- 



X). 



s-dz = 



Put V(2a — •'t) = X, then 



fjcdx V(2a — x) — 'ips'dz — iah-a ^ 



Substitute for s its value, and take the integral between the 

 limits — 



Firstly, .r = 0, and j; ^ 2a : then 



J^ xdx V(2a-^) = (2a)5.2 (-—j = «' • j-5 v2. 



