1919] 



RURAL ENGINEERING. 



885 



Weight and strength of manilla rope. 



[Figures apply to three-strand rope, medium laid. Four-strand rope may rim up to 7 per cent heavier 

 and may show 95 per cent of the tabulated strength. ] 



Effect of artificial light on the growth and ripening of plants, J. L. R. 

 Haydex and C. P. Steinmetz {Gen. Elect. Rev., 21 (1918), No. 3, pp. 232-236, 

 figs. 5; ahs. in Set. Abs., Sect. B— Elect. Engin., 21 {1918), Xo. 2^5, pp. 189, 

 190). — An experiment in an orchid house with beans is reported, in which gas- 

 filled IMazda lamps were used as the .source of light. Five 500-watt lamps 

 were suspended in a row 36 in. above the ground and 17 in. apart and were 

 kept burning day and night for 44 days, consuming 2.5 kw. Two lamps were 

 kept burning 29 days longei'. The hothouse temperature was raised 2° C. 

 by the heat of the lamps. The power consumption over the bed was 55 watts 

 per square foot and the intensity of illumination about 700 lumens per square 

 foot of ground, thus approaching direct sunlight. 



The rate of plant growth and development was nearly doubled over the plat 

 receiving only daylight, but at high cost. It is thought that such artificial 

 illumination might pay for itself when used for raising products temporarily 

 of high value for special purposes. 



Agricultural tractors, A. E. L. Chorlton {Engineering [London], 105 {1918), 

 No. 2714, pp. 7-10. Jiga. 12; ahs. in Sci. Abs., Sect. B — Elect. Engin., 21 {1918), 

 No. 24.5. pp. 175-177). — The work of an agricultural tractor is classified as road 

 work, land work, and farmstead work. Considerable data bearing on these 

 classifications are summarized and discussed. 



The basic factors in road work are considered to be adhesion and resistance. 

 Tests with steel and rubber tires on ordinary roads showed a maximum ad- 

 hesion of 0.56 for steel and 0.6 for rubber tires. In designating a tractor for 

 road work, it is concluded that the propulsive effort can not exceed 0.45 times 

 the weight on the driving axle for steel tires and 0.5 for rubber tires. The 

 data indicate (1) the desirability of providing enough engine power to permit 

 the use of 4-share plows, (2) the value of a large flywheel effect to equalize 

 the load, and (3) the advantage of using more efficient gearing. Fundamental 

 values for the multipurpose tractor for English, conditions are taken to be as 

 follows: For road work, power requirement from 18 to 20 h. p., for land work 

 23 to 25 h. p.. and for farmstead work 20 to 25 h. p. Other general features of 

 design are discussed. 



