3917] EURAL ECONOMICS. 491 



liiMcadam road, and was practically constant, for all speeds considered, on any 

 i;iven road. The iiupacL resistance increases with the velocity, with the total 

 weight of vehicle, and with increasing road-surface roughness. In these tests 

 vlio impact resistance of good asphalt or bitulitliic or other smooth pavement 

 wiis practically negligible, and reached its highe.st values on granite-block roads 

 Willi sand-tilled joints, and on badly-worn macadam pavements. The rate of 

 incre;ise of impact resistance with speed was most marked ou the roughest 



" At the vehicle speed of 20 km. (12.4 miles) per hour, the air resistance 

 for the vehicle tested, assumed to be dependent only on the speed, was roughly 

 0.11 per cent equivalent grade ; that is, from 4 per cent of the highest to 12.5 

 per cent of the lowest total tractive resistance. 



"The following pavements are enumerated in the order of their desirability 

 for vehicle operation from the point of view of tractive resistance at 20 km. 

 i)er hour, as found in this investigation: Asphalt, wood block, hard, smooth 

 macadam, brick block, granite block with cement-filled joints, cindei*, gravel, 

 «nd granite block with sand-filled joints. 



" The equivalent grade at 20 km. per hour of a badly worn macadam road was 

 found to be nearly three times as great as that of the best asphalt road tested. 

 This means, at this speed, a consumption of energy at wiieel treads of nearly 

 three times as much on level, poor macadam roads as ou level, good asphalt 

 roads. Increasing the gross weight of the \ehicle V^y 12 per cent through load 

 was found to have no eft'ect on tractive resistance within the observed speed 

 lindts for smooth roads in good condition; but on rough roads, a distinct in- 

 crease in tractive resistance with this extra weight was observed. The pres- 

 ence of a layer of dust, say 1 cm. thick, on a fair macadam road, was found 

 to increase the equivalent grade of tractive resistance at all tested speeds by 

 :.bout 0.15 per cent. A freshly tarred, and therefore soft, tar-n)acadam road 

 was found to have an increased equivalent tractive resistance at substantially 

 all tested speeds of about 0.5 per cent. The tires in this case sank about 0.8 

 in. into the roadbed, the gross car weight being 4,710 lbs. The total range of 

 tractive resistance equivalent grade covered in the tests was from 0.93 per cent 

 i)n the best asphalt road at lowest speed to 2.7 per cent on the worst macadam 

 road at nearly the highest speed." 



First national farm tractor directory, compiled by C. E. Stoni? {New York: 

 The Ayricultural Press, 1916, pp. 8). — This is a complete list of farm tractors, 

 their manufacturers, horsepower, type, traction, and other particulars. 



Modern systems of independent lighting and heating (Nature [London], 

 ii6 {1916), Nos. 2410, pp. 522-524, figs. 5; 2J,11. pp. 652, 553, fign S; 21,12, pp. 

 577, 578, fig. 1). — Oil, oil gas, petrol air gas, acetylene, and electric lighting 

 sy.stems for country homes are described and illustrated. 



RURAL ECONOMICS. 



The farmer's labor income, P. L. Vogt {Amer. Eeon. Rev., 6 (1916), No. 4, 

 pp. SOS-822). — After discussing the data available from the various studies in 

 connection with the Office of Farm Management of the U. S. Department of 

 Agriculture as to the farmer's labor income and additional information as 

 furnished by the Census, the author concludes as follows : 



" The data presented indicate that, while at the present time labor incomes 

 of farmers compare favorably with those in urban industries, the institution of 

 private ownership of land does not offer much hope for further increase of 

 these incomes unless the system of owner operation can be pre.served. Laborers 

 are evidently not benefiting by the economic changes taking place. Tenants 



