CHAP. IV., 6.] MECHANICS (OF FLUIDS). MR RUSSELL M. FOURNEYRON. 



91 



Compared 



by 

 land and 

 Mr Airy. 



(422.) 

 Peculiar 

 effect of 

 wave trans- 

 mission on 

 canal navi- 

 gation. 



(423.) 

 Practical 



results. 



pear whether the disturbed or undisturbed depth is 

 to be taken. The analysis of Mr Airy seems to show 

 a depth somewhat greater than that due to the 

 utmost effect of disturbance is to be preferred. Mr 

 Russell also made experiments on the propagation of 

 waves in channels of different forms of section. Pro- 

 fessor Kelland has given a very simple expression 

 for the velocity of the wave in this case, 1 which on 

 the whole agrees with experiment. 



Sometime about the year 1830, attention was 

 drawn to a singular fact connected with the resist- 

 ance of water in the case of canal navigation. It 

 was first noticed I believe in Scotland, probably on 

 the Forth and Clyde Canal. It amounted to this, 

 that whereas at moderate or rather slow velocities, 

 the resistance to a boat increases with the square 

 of the velocity, after a certain point, not differing 

 very much from 7 miles an hour, the resistances not 

 only cease to increase according to the same rapid 

 law, but actually diminish to some extent when the 

 speed is greater. Different experiments were made 

 by the canal proprietors with a view to meet in some 

 degree the active competition by railways, then com- 

 mencing. Mr Russell was employed by the directors 

 of the Forth and Clyde Canal, and to his experiments 

 we now refer. It appears from his tables that the 

 resistances increased on the whole faster than the 

 squares of the velocities up to 7i miles an hour, 

 when they suddenly diminished between 7 and 8J 

 miles an hour by one-fifth part in one experiment, 

 and by no less than one-third in another. 2 It was 

 not until about 12 miles an hour, that the resistance 

 reached the same amount as at 7i miles. 



The occurrence of this singular transition was at- 

 tended with a phenomenon easily noticeable. In 

 every ordinary case a boat in a canal drives a wave 

 before it, which is in fact a heap of water resisting 

 the boat by increasing the pressure against its bows, 

 which wave may be called a forced wave, having this 

 peculiarity that it travels with the speed of the boat 

 and never quits it ; whilst a free wave, by whatever 

 cause excited, is propagated at a rate depending only 

 on the dimensions of the canal, particularly its depth. 

 Now the diminished resistance takes place when the 

 boat is by the force of traction partly drawn out of the 

 water, and lifted up upon the wave to which its own 

 motion gives rise. It is said to ride upon the wave, 

 and the head of water pressing against its bows is 

 visibly diminished. The most advantageous rate of 

 transport was found to be about one-third greater than 

 that required merely to mount the wave, which last 

 depends principally on the depth of the canal. Thus 

 on three different canals, 3, 5, and 9 feet deep, 

 the most advantageous velocities were 8, 11, and 

 15 miles an hour. The actual velocities of the 

 free wave were ascertained by Mr Russell in an in- 



genious and satisfactory manner. When the boat is 

 dragged to most advantage, the draught of water is 

 less at the stem and stem than in the centre. All 

 these circumstances have been very ingeniously and 

 satisfactorily explained by Mr Airy in his paper on 

 Tides and Waves, articles (404-411). 



Many persons (amongst whom are Colonel Henry (424.) 

 Beaufoy, Mr Scott Russell, and the American ship- Forms of 

 builders) have bestowed much attention on the forms shlp3< 

 of vessels for ensuring speed, especially by the avoid- 

 ance of waves of various kinds generated by steam- 

 vessels in motion. Every one who can compare the 

 performance of such vessels during the last twenty 

 year's, and the still surface which waters navigated 

 by steam vessels now present, as if they were merely 

 cut open and closed again before and after the passage 

 of the ship, instead of being tossed into dangerous bil- 

 lows consuming uselessly the propelling force, will 

 readily admit that, however imperfect the theory, prac- 

 tical art has made real progress in this direction. 



III. Improved Hydraulic Machines Turbine. (425.) 

 Before concluding this section, I will refer to the Improved 

 most considerable improvement made of late years 

 in the application of hydraulic pressure to motive 

 purposes, and I shall couple it with the names bine, 

 of two French engineers, MM. FOURNEYRON and 

 PONCELET, the former the inventor of the Turbine 

 (the machine referred to), at least in its improved 

 practical form ; the latter an important contributor 

 to the useful application of hydraulics, an accom- 

 plished mathematician, and the author of several 

 standard works connected with industrial mechanics. 



The defects of common vertical water-wheels, (426.) 

 whether overshot or undershot, are so great and Defects of 



so notorious, that only their simplicity, and the common 

 , . ' ' r J> water- 

 tact that in very many cases water-power costs wheels 



next to nothing, and may be squandered with im- Barker's 

 punity, could justify their use. The advantage of miUt 

 using the simple pressure of a fluid as a moving 

 power had been foreseen in that application of re-ac- 

 tion called Barker's Mill; which, though well known 

 in models, was seldom if ever applied in practice. 

 Mathematicians were, however, aware that it offered 

 important advantages. Of late years a patent has been 

 taken out in Scotland for a modification of it, which 

 is found, I believe, to work well. But the Turbine 

 or horizontal water-wheel imagined by Burdin and 

 Fourneyron, and brought to a high state of perfection 

 by the latter about the year 1833, appears to exhaust 

 ail that is valuable in this mode of applying water. 



Referring to other parts of the Encyclopaedia (427.) 

 for the details, I may here explain generally that Fourney- 

 the Turbine consists of two parts, one a fixed cy- ron ' 8 tur " 

 linder or drum of small height compared to its 

 diameter; the other a portion of a cylinder ex- 

 terior to the former, and moveable round it, so that 



bine. 



1 Velocity = V 9 ^ ', where A is the area of section of the canal, b the breadth of the water at the surface, and g the accele- 

 rating effect of gravity. Edinburgh Trans, vol. xiv. 



2 Edin. Trans., vol. xiv., p. 48. 



