766 



Popular Science Monthly 



stream and found that in one minute the 

 chip moved 24 ft. down the stream. At 

 this point the stream had an average width 

 of 12 ft., and an average depth of 3 ft. I 

 then estimated that Q in cubic feet per 

 second would be the width of the stream 

 multipHed by the depth and by the speed 

 of the chip in feet per second, which is 

 12X3X24/60 or 14.4 cubic feet per second. 

 Because of rapids or other influences, 

 such as great irregularities in the shape of 

 the stream, it is not always possible to 

 determine Q by this method. A satisfactory 

 way is to consider the falls as a weir. To 

 make our proposition general we will say 



JAN FEB MAR APS MAY JUN JUL AUG SEP OCT NOV DEC 



Chart showinpf'the monthly variations in cu- 

 bic feet per second for a period of one year 



that the width of the stream as it goes over 

 the falls is W feet and that the depth of 

 the water as it flows over the edge or 

 crest of the falls is C inches. It may 

 then be shown that the quantity of water 

 flowing over the falls in one second is 

 WC 5\/^/i5 cubic feet. Attention is called 

 to the fact that the denominator 15 is the 

 same as in the expression for horsepower 

 developed. Care should be taken to get 

 the total height C, as the depth of the 

 water at the very edge of the falls is apt 

 to be a little under the true depth. 



The stream which we gaged by the chip 

 method has in it a fall 12 ft. wide and the 

 water has a depth of 7 in. as it flows over 

 the edge. From the formula just given Q 

 would be 12X7XV7/15 which is 14.8 

 cubic feet per- second, or approximately 

 the same result which was obtained by 

 the chip method. 



The total height of the fall is 14 ft. 

 so that the horsepower developed would be 

 QH/15 or 14X8X 14/15 which is 1.4, or just 

 slightly under one and one-half horsepower. 



Remembering that one horsepower is 

 746 watts and that the efficiency of a 



generator of this small size would not be 

 over 70 per cent, it will be seen that about 

 750 watts power would be available for use. 

 This amount of power would light eighteen 

 forty-watt tungsten lamps, which is all 

 that would be required in an average house. 



There is one other point to be considered 

 and that is the constancy of flow. The 

 flow of streams varies greatly over different 

 periods of the year, as well as from year 

 to year. An illustration of this is shown 

 in the accompanying diagram which is a 

 plot showing the average flow per month, 

 in cubic feet per second, taken over a period 

 of one year. Such a curve is called a hydro- 

 graph. The hydrograph for this stream 

 shows that the month having the greatest 

 flow was March and that the month of 

 minimum flow was January. 



In an actual installation the question of 

 pondage, or water-storage is an important 

 one. By building a large pond, or by using 

 natural basins it is possible to conserve 

 the water so that it will be used only as 

 required. This would mean a greater sup- 

 ply and consequently more power when it 

 was actually needed. Waterpower develop- 

 ments include many questions of this sort 

 but they are all outside of the scope of this 

 article. The principal point to be remem- 

 bered here is that horsepower is cubic feet 

 per second multiplied by the head in feet 

 divided by 15, P = QH/i5. 



The installation shown in the illustrations 

 is that of a power plant on a very small 

 stream where it was not convenient to use 

 a dam to store up the water for the power. 

 The use of storage-batteries gave the same 

 result. The water wheel is run all day 

 long, generating all the power the stream 

 affords and using that power to charge the 

 storage-batteries, which were only used at 

 night, except in the fruit storage bins where 

 light was needed at any time. 



The battery consists of 16 cells, 80 am- 

 peres. The switchboard carries an ampere- 

 hour meter that shows the condition of the 

 battery; also an ammeter, which shows if 

 more or less current is being used than is 

 being generated; and an automatic switch 

 which prevents the system from damage 

 due to disturbances such as short circuits,- 

 lightning, etc. The outside wiring is carried 

 on poles from the generator-house to the 

 switchboard and from there to the various 

 buildings that are lighted by the plant — 

 residence, fruit storage building, cooperage 

 shed, barn, carriage house and garage — six 

 in all. 



