788 EXPERIMENT STATION RECORD. 



and lower power. Tests of the low-pressure engine having a cylinder diameter 

 of 36 in. and a 36 in. stroke showed a steam consumption per brake horsepower 

 hour which compared very favorably with the results obtained from tests of 

 several higher and lower power exhaust steam turbines under similar conditions. 



It is stated that the whole success of the small low-pressure engine depends 

 on the availability and maintenance of a high vacuum, for which purpose spe- 

 cially designed air and hot well pumps are employed. 



Windmill electric lighting and power, W. Manikowske (Nortfi Dakota Sta. 

 Bui. 105, pp. 39, figs. 21).— This bulletin, a thesis for the degree of bachelor of 

 science, calls attention to the convenience of electricity for lighting and power 

 on the farm and describes a windmill electric lighting and power plant which 

 it is claimed has given satisfactory operation for 2 years. The windmill, con- 

 sisting of a 16 ft. wheel on a 20 ft. tower, is of the power tyi^e and drives a 1.4 

 kilowatt 150 volt, 1,800 r. p. m. special wound generator. A speed regulator so 

 to control the varying speed of the mill as to produce a constant speed for gen- 

 eration is used, which consists essentially of a friction drum attached to the 

 main drive shaft and 2 weighted arms, with friction shoes at one end, con- 

 nected to the driving pulley, which transmit the power from the friction drum. 

 When the speed increases so that centrifugal force causes the weights to fly 

 outward the friction shoes are released from the friction drum, thus keeping 

 the driving pulley below a certain speed. 



The other necessary equipment is described and data are given from tests by 

 E. C. Murphy (E. S. R., 13, p. 195) showing that a power mill is more efficient 

 than a pump mill and that the load of the windmill must increase in direct 

 proportion to the wind velocity if maximum efficiency is to be obtained. In 

 addition to the automatic speed regulator the essential points to be considered 

 for success with a windmill electric light and power outfit are stated as fol- 

 lows : A good wind velocity (20 miles per hour) must be at hand at least on an 

 average of 6 hours during every week. An automatic cut-out and cut-in be- 

 tween the generator and storage battery is deemed necessary, as is also an 

 automatic self-regulating switchboard. 



Wind velocity data from North Dakota show the economic value of the 

 windmill as a source of farm power in that State. By a comparison of costs of 

 producing electricity by windmills and gasoline engines in North Dakota it is 

 estimated that the total cost of a kilowatt hour as produced by wind power is 

 about 5 cts. and by a gasoline engine 14.8 cts. The initial cost of the 2 outfits 

 is considered practically equal. 



Inaccuracies of indicators, J. G. Stewart {Power, SI (1913), No. 2^. pp. S51- 

 853, figs. ^). — Extracts from a paper presented before the Institution of 

 Mechanical Engineers at London give the results of experiments and descrip- 

 tions of special apparatus employed in the determination of errors in indicators. 

 It is shown that the indicator is subject to systematic errors of 2 distinct types : 

 (1) The indicated pressure may not be that corresponding to the pressure in 

 the cylinder, either because of friction or to inertia of the moving parts or to 

 both; (2) the position of the drum may not be that corresponding to the posi- 

 tion of the piston, because of stretch of the string or to straining in other parts 

 of the indicator gear. 



It is concluded that for important deductions from indicator diagrams the 

 instrument should be tested and adjusted for these errors. 



Mechanical safety devices in agricultural work, H. Puchner (Landw. 

 Eefte, 1913, No. 16-17, pp. 74, figs. 79).— A large number of safety appliances 

 are illustrated and described which may be applied to agricultural implements 

 and machinery. 



