ON PADDLE WHEELS. 141 



figures, the peculiarity of action arising from this disposition of the paddle boards becomes 

 evident, but more particularly in Fig. 5, where the floats are immersed for a longer time. 

 One set of floats is there seen entering the water at a, b, c, d, the position of which is shown 

 at a', b', c", d', after an interval of one-sixteenth of a revolution ; and it is apparent that, while 

 the outer board, a, is moving to the position a', the next board, b, almost follows the track of 

 the former to arrive at b' ; in the same manner the third follows the second, and the fourth 

 the third, until they arrive at the middle of the stroke, when they diverge so as to perform 

 the last half of the stroke independent of each other's motions, and emerge from the water at 

 such a distance from each other, that the water which is not thrown off with violence can run 

 off more readily than from the broad float of the common wheel. It thus appears that very 

 little more effect is produced during the first half of the stroke of one set of boards than would 

 be produced by the outer board alone, and during the second half the effect is about equal to 

 that of a common float equal in size to the sum of those which form a set. We conclude, 

 therefore, that the shock received by the floats on entering the water must be reduced nearly 

 to that of the outer board, but that this advantage is gained at the expense of a considerable 

 portion of the effect, in consequence of which the wheels must require a greater surface of 

 paddle board than common wheels. There may also be a little advantage in the manner the 

 floats leave the water, but that, if any, must be very trifling. It is evident that no theoretical 

 calculation can be made of the effect of this wheel, its action being precisely similar to that of 

 the common wheel, except that all but the outer boards move during a considerable part of 

 their stroke in troubled water, whereby a loss of resistance is sustained, the amount of which 

 cannot be computed. It remains, therefore, to be decided by experience whether the dis- 

 advantages of this wheel are overbalanced by the advantages which it seems to possess. 



It is remarkable that since the adoption of this wheel, when Mr. Galloway made them with 

 six or seven bars in each set instead of the ordinary paddle boards, this number has been very 

 much reduced : those now used in Her Majesty's service have only two boards in a set, every 

 reduction having been found to be attended with advantage ; they cannot, however, carry their 

 improvements any farther without annihilating the principle of the wheel altogether, and 

 returning to the common wheel. 



It should here be observed, that in the summer of the year 1837, before these wheels were 

 adopted in Her Majesty's service, a numerous series of experiments were made at Woolwich 

 on Her Majesty's steamer 'African,' under the superintendence of Mr. Ewart, inspector of 

 steam machinery, some with the common wheel, and some with Field's, in order to ascertain 

 the comparative merits of the two wheels. The results of these experiments were not allowed 

 to be publicly known, because they were not complete ; but Mr. Ewart was so well satisfied 

 with the success of the trials, that Her Majesty's steam vessels ' Rhadamanthus,' ' Dee,' 

 'Tartarus,' and 'Meteor/ were immediately fitted with Field's wheels, each with two boards 

 in a set. From what we have been able to learn from persons who were present at the 

 experiments alluded to, some very anomalous results were obtained, such as less velocity of 

 the engines and greater speed of the vessel ivith less float, all other circumstances being the 

 same. 1 



1 This is a proof that the accuracy of the mile trials cannot be implicitly relied on, at least as they have been made till 

 now ; perhaps they might be made more practically useful, if greater attention were paid to the various circumstances which 

 affect the results. 



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