ON PADDLE WHEELS. 157 



whose axis is fixed to the spring beam in a line with the main shaft, and passes through the 

 centre of the outer boss of the wheel ; the crank head is shown at E, abaft the axis of the 

 wheel, and slightly elevated above it ; on this revolves a collar, round the circumference of 

 which are pin-jointed the guide rods, h, h, h, &c., each of which is pin-jointed at its other end 

 to the extremity G, of one of the stem levers. One of the guide rods, g, is an exception, being 

 keyed, and not pin-jointed, as the others are, to the revolving collar, and is called the driving 

 rod, because by its means the collar is driven, or made to revolve at the same time as the 

 wheel. It acts upon one of the floats in the same manner as the other guide rods. 



The object of this combination is evidently to regulate the inclination of the floats by 

 alternately increasing and diminishing the distance between the spindles and the excentric 

 centre E, to obtain which centre is the sole intention of the crank ; but, as it was found im- 

 practicable to make all the guide rods as well as the driving rod radiate from that centre, the 

 revolving collar was added in order to obtain excentric centres for the rest of the guide rods, 

 and this collar ought to be as small as it can conveniently be made, for a large one would cause 

 a variation in the action of the different floats. 



There is a great advantage in the mode of hanging the floats in this wheel, which cannot 

 be applied to Buchanan's or Oldham's, viz., that the spindles, being fixed in the frames of 

 the wheel, contribute greatly to its solidity, and the stem levers, being situated in the centre 

 of the floats, to which they are firmly fixed, are much more efficient instruments to guide the 

 floats than the cranks in the two other wheels, which, besides being on one side and at a 

 considerable distance from the floats, have very weak bases in consequence of their axes 

 having to turn in bearings in the framing of the wheel, and are thus very liable to ring, which 

 must be very injurious to the action of the wheel, as all the floats are guided by one single 

 piece. 



It is astonishing that Morgan's wheel should ever have been for a moment confounded with 

 Buchanan's, the principle and construction of the two differing from each other so widely as 

 they do. The difference of principle has been already pointed out (see page 147), and in 

 construction they differ materially : in Buchanan's wheel the pin-jointed guide rods are entirely 

 wanting, and the revolving collar is enlarged to the size of the principal framing of the wheel ; 

 the levers by means of which the floats are feathered must be equal in length, in Buchanan's 

 wheel, to the distance between the centre of the wheel and that of the excentric, while in 

 Morgan's they never are ; in Buchanan's wheel the spindles revolve uniformly in their bearings, 

 for which reason the cranks must be outside the wheel, as otherwise they could not pass, 

 while in Morgan's the floats vibrate on their spindles, which motion allows of the stem levers 

 being situated in the interior of the wheel. 



Oldham's wheel is still more distinct from Morgan's in construction, by reason of the gear 

 for causing the excentric axis to revolve ; it resembles it, however, much more in effect, as 

 the floats are constantly changing their inclination, but the fixed law, that this must always be 

 exactly half that of the radius, allows of no deviation, while in Morgan's wheel there exists no 

 fixed relation between the inclination of the float and that of the radius. 



We shall presently have to describe another wheel, which has been declared to be the same 

 as Morgan's, which it resembles very much ; namely, that invented by M. Cave, engineer, at 

 Paris, to whose kindness we are indebted for a drawing of his wheel. In this all the guide- 



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