572 



SCIENCE 



[N. S. Vol. XXXVII. No. 954 



4 in. brick on 6 in. concrete foundation, $1.71 to 

 $2.34. 



4 in. brick on 4 in. concrete foundation, $1.47 to 

 $1.73. 



During the last three years the following aver- 

 age price has been paid. 



5 in. brick laid on natural sand foundation, $1.27 

 per sq. yd. 



5 in. brick on 8 in. sand or gravel foundation, 



$1.58 per sq. yd. 

 4 in. brick laid on 4 in. concrete foundation, 



$1.60 per sq. yd. 



Average life of five inch brick on sand founda- 

 tion is taken from the city's experience to be 

 fifteen years. Four-inch brick on sand foundation 

 is assumed as twelve years. From this data it is 

 calculated that four-inch brick can be laid on four- 

 inch concrete as economically as the five-inch on 

 natural sand foundation if the life will be twenty- 

 two years. Four-inch brick can be laid on six-inch 

 concrete as economically as five-inch brick on 

 eight inches of sand or gravel foundation if its 

 life is eighteen years. 



It is concluded that when conditions are favor- 

 able a five-inch brick laid upon a good natural 

 sand foundation will form the cheapest form of 

 brick pavement, but in all other cases one with a 

 concrete foundation will prove the most economical. 



Some Considerations Affecting the Interaction of 

 Motor-vehicle Wheels and Boad Surfaces: De. 

 L. I. Hewes, chief, division of economics and 

 maintenance. Office of Public Roads, U. S. De- 

 partment of Agriculture, Washington, D. C. 

 In this paper, the author suggests the fundamen- 

 tal work equation 



(1) 



=/, 



where h is effective horsepower developed at the 

 tires of the motor wheels of an automobile, v is 

 the velocity, and / the total resistance. This equa- 

 tion obtains on a level at constant speed and with 

 the air resistance neutralized by a wind current 

 parallel to the velocity of the machine. It is im- 

 portant to determine the nature of the resistance 

 /, which is in a sense a road coefficient, as it must 

 vary for the same automobile on different roads. 

 The resistance to the motion above described can 

 not be solely due to the action of gravity on the 

 weight of the machine as much as assumption de- 

 mands a constant resistance for all speeds on the 

 same road. A table is presented showing the re- 

 lation between effective horsepower, velocity and 



resistance of traction. This table was published 

 in Le Genie Civil, Vol. LXI., No. 14, p. 276, and 

 exhibits the relation of equation (1). It is the 

 record of tests made in 1912 in Paris on a Berliet 

 truck. 



The author discusses two sources of resistance 

 which must be included in the symbol /. First the 

 resistance which is developed by the motion of the 

 points on the automobile tire not in contact with 

 the ground and which strike small particles with 

 a positive forward velocity. It is pointed out that 

 a point on the periphery of a tire moves in a cycloid 

 and at the instant of contact has zero velocity, 

 whereas points immediately adjacent to the periph- 

 ery and not in contact with the ground move in 

 rolling curves with velocities having considerable 

 horizontal components which may produce small 

 and continuous shocks, which, owing to the varying 

 magnitude of the velocities in the same vertical 

 cross-section, can produce twisting action upon 

 small particles comparable to the ' ' English " of a 

 billiard ball and thus throw small material to one 

 side of the path. Table of velocities of points at 

 . varying vertical distances from the road surface 

 follows. A second source of resistance is described. 

 This resistance is due to the fact that the pneu- 

 matic tire which is in the form of a torus is not 

 applicable to road surfaces without deformation. 

 The increment of tensions in the tire material due 

 to such deformation is described and it is pointed 

 out that such rubbing action on the road surface, 

 while simultaneous, is continuous and the sum of 

 such effects must cause a portion of the resistance 

 /. The author concludes that on account of both 

 sources of resistance it is desirable to preserve the 

 enamel of the road surface intact and free from 

 all loose particles, and further that the interaction 

 of road and tire must continue unfavorable both 

 to road and tire, unless the section of the tire is 

 made trapezoidal. 



Bituminous Surfaces on Brich Pavements: Ellis 



R. Button, assistant city engineer, Minneapolis, 



Minn. 



The use of a bituminous coating on the surface 

 of old and new brick paving is desirable and 

 beneficial. It gives a more pleasing appearance 

 to the street, reduces the noise, affords better 

 foothold for horses — and lessens the wear of the 

 brick. 



A bitumen which would be satisfactory for this 

 purpose should be of a very adhesive quality all 

 the time, under all conditions of moisture and 

 temperature, and should not become excessively 



