168 Notes on Small Motors. 



the passages so formed as to have as large a hydraulic radius 

 as possible. 



Fig. 2 represents a form of reaction wheel devised by the 

 writer of this paper, and which is thought to fulfil the above 

 conditions more perfectly than any hitherto adopted. There 

 are no abrupt bends. The velocity of now gradually increases 

 in the tapered pipe, attaining its maximum at the terminal 

 jet, and by adopting a circular section throughout, and hav- 

 ing but one jet instead of two or more, as in previous forms, 

 the hydraulic radius is kept as large as possible. 



In the case of every hydraulic motor supplied with water 

 through a pipe, there is a certain critical velocity of flow in 

 the pipe at which the maximum development of power 

 will take place. If the velocity be less than this, the power 

 will be reduced and the efficiency of the system somewhat 

 increased. In other words, the quantity of water expended 

 will be reduced in a higher ratio than the power. If the 

 critical velocity be exceeded, the expenditure of water will 

 be enhanced, but both power and efficiency reduced. 

 Adopting Darcy's views as to the friction of water on the 

 walls of the pipe, this critical velocity can be shown by the 

 aid of the differential calculus to be '575 of the full velocity 

 when the pipe is discharging freely, and at this speed one- 

 third of the total head of the water will be employed in 

 overcoming friction in the pipe, and the remaining two- 

 thirds be available for the production of motive power. 



The motor shown (Fig. 2) has been successfully applied to 

 driving a small lathe for turning either wood or metal. At 

 the outset, however, it was found that with such an irregular 

 resistance as that of turning, inconvenient variations of 

 speed took place, and water was wasted when the wheel 

 was racing. This defect was partly remedied by the use of 

 a fly-wheel, but was eventually more thoroughly obviated by 

 means of a jet, the dimensions of which were altered by the 

 centrifugal action of a weight, which, with its opposing 

 spring, was so adjusted as to form an approximately isochro- 

 nous system. The mechanical details of this contrivance are 

 shown in Fig. 3. 



The following tabulated statements show — 1. The .par- 

 ticulars and results of experiments to determine the power 

 and efficiency of the motor; 2. The comparative cost of 

 motive power per 1,000,000 ft. lbs., as derived from various 

 sources ; and 3. The approximate power required in order to 

 perform several of the functions of a small motor. 



