Mr J. G. Stuart on the Turbine Water- Wheel 167 



agree very satisfactorily with the statements of the different Continental writers 

 who have handled the subject experimentally ; and, reasoning from a source 

 Independent of experimental results, the Committoe see additional grounds for 

 placing confidence in those statements, as well as in that of Mr Stuart. The 

 grounds here alluded to, rest on the circumstances attending the arrangement 

 of common bucket and breast-wheels. In all such casec, water acts by its gravity 

 alone; hence such wheels are usually restricted to velocities of 6 to 8 feet per 

 second, and hence also, the water must have acquired a corresponding volocity 

 before it enters the wheel. This preparatory step takes from the height of the 

 fall a quantity varying from one to two feet ; at the bottom of the fall, also, there 

 is a loss consequent ujion the prevention of back-water, amounting at least to 

 half the depth of the shrouding, or from 6 to 9 inches, making a total redaction 

 of fall of from 2 to 2i feet. 



With the Turbine, the engineer gets free of this loss of fall, because the ma- 

 chine takes up, if well constructed, every inch of the height ; or, according to the 

 views of the Continental writers, it may even yield effects beyond the natural 

 fall, by working the turbine under the surface of the tail-water. Upon this 

 last point, the Committee have some misgivings ; but from the grounds above 

 stated, that of rendering every inch of the fall available, they see good reason 

 to expect uniformly favourable results from Turbines properly constructed and 

 regulated. 



It will readily appear, that the advantage, here dwelt upon, bears with greatest 

 effect upon low falls ; and since the reduction of the fall (for common wheels) 

 will be nearly the same for all heights, it follows, that the loss bears a much 

 larger proportion to the entire height in low, than in high falls. Thus, in a fall 

 of 6 feet, one-third may be considered as lost ; but in one of 30 feet the loss 

 would be only ^-^ or t^. It follows, from these observations, that the Turbine 

 will be most economical, in respect to power, in falls of from 1 foot up to 10 or 

 12 feet. As the fall becomes higher, the advantages diminish, and it is more 

 than probable, that, from 20 to 30 feet, a bucket-wheel is to be preferred. Up- 

 wards of 30 feet, and especially for great heights, the Turbine again becomes 

 economical, but on other grounds ; here the advantages will lie in the cowyxtra- 

 tively small cost of erection, com-pv^red with the power attainable from great heights- 

 These considerations, independently of any advantage arising from the inter- 

 nal mechanism of the Turbine, seem to afford still surer grounds of confidence 

 in this machine, under the limits here specified. 



In conclusion, the Committee have great pleasure in expressing their appro- 

 bation of those exertions of Mr Stuart, which place him as the first in this country, 

 to have adopted " Fourneyron's " beautiful invention ; and, from the fortitude 

 and persevering skill exhibited in the pursuit of his object, crowned as it is with 

 a successful accomplishment, Mr Stuart is, in the opinion of the Committee, de- 

 serving of the best consideration of the Society. 



James Slight, Convener. 

 John An&seson. 

 Edinburgh, Jun4 9. 1846. 



