April 6, 1917] 



SCIENCE 



343 



est, to 12.5 per cent, of the lowest, total trac- 

 tive resistance. 



7. The following urban pavements are enu- 

 merated in the order of their desirability for 

 vehicle operation from the point of view of 

 tractive resistance at 20 km. (12.4 miles) 

 per hr., as found in this investigation. (1) 

 asphalt, (2) wood block, (3) hard smooth 

 macadam, (4) brick block, (5) granite block 

 with cement-filled joints, (6) cinder, (7) 

 gravel, (8) granite block with sand-filled 

 joints. 



8. The equivalent grade at 20 km. (12.4 

 miles) per hr. of a badly worn city 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 wheel treads, of nearly three times 

 as much on level poor macadam roads as on 

 good level asphalt roads. 



9. Increasing the gross weight of the vehicle 

 by 12 per cent, through load, was found to 

 have no effect on tractive resistance within the 

 observed speed limits for smooth roads in good 

 condition; but on rough roads, a distinct in- 

 crease in tractive resistance with this extra 

 weight was observed. 



10. The presence of a layer of dust, say one 

 cm. thick, on a fair macadam road, was found 

 to increase the equivalent grade of tractive 

 resistance, at a speed of 20 miles (12.4 km.) 

 per hr., from 1.17 to 1.32 per cent. 



11. A freshly tarred and therefore very soft 

 tar-macadam road was found to have an in- 

 creased tractive resistance equivalent grade, 

 at substantially all tested speeds, of about 

 0.5 per cent. The tires in this case sank 

 about 0.8 inch (2 cm.) into the road-bed, the 

 gross car weight being 2,140 kg. (4,710 lb.). 



12. The total range of tractive resistance 

 equivalent grade covered in the tests, was 

 from 0.93 per cent, on the best asphalt road, 

 at lowest speed, to 2.7 per cent, on the worst 

 macadam road, at nearly the highest speed. 



13. The results indicate, as has already 

 been pointed out by other observers, the im- 

 portance of constructing and maintaining 

 smooth, hard and clean roads, from the point 

 of view of tractive resistance. Low tractive 



resistance means small gasoline consumption 

 for gasoline trucks, and a reduced electricity 

 expense or greater daily mileage with electric 

 trucks. 



14. Other problems which are of practical 

 importance to vehicle designers and operators, 

 and which require further investigation are 

 the following: 



(a) Tractive resistances on country roads. 

 (h) Tractive resistances to vehicles with differ- 

 ent wheel tires. 



(c) Tractive resistances of urban roads at low 



speeds from to 10 miles per hour (16 

 km. per hr.). 



(d) Tractive resistances at speeds higher than 



15 miles per hour (24 km. per hr.). 



(e) Tractive resistances for high-capacity 



trucks. 



15. The results of the tests here reported 

 have been found to be in substantial agree- 

 ment with those obtained by other observers 

 employing somewhat different methods; but 

 the analysis of tractive resistance into its 

 components here presented appears to be new, 

 and is recommended for use in similar inves- 

 tigations or tests. 



16. The writers are indebted to Mr. Thomas 

 A. Edison and also to the Gould Storage 

 Battery Co. for funds by which the research 

 was made possible. A. E. Kennelly, 



O. E. SCHURIG 



Massachusetts Institute op Technology, 

 Cambridge, Mass. 



SOCIETIES AND ACADEMIES 



THE BIOLOGICAL SOCIETY OF WASHINGTON 



The 563d meeting of the society was held in the 

 assembly hall of the Cosmos Club, Saturday, Jan- 

 uary 13, 1917, called to order by President Hay at 

 8 P.M., with 45 persons in attendance. 



On recommendation of the council Dr George W. 

 Field, Biological Survey, was elected to member- 

 ship. 



President Hay announced the membership of the 

 Publication Committee; C. W. Eichmond, J. H. 

 Eiley, Ned Dearborn, W. L. McAtee ; and the mem- 

 bership of the committee on communications : Wm. 

 Palmer, Alex. Wetmore, E. E. Coker, L. O. Howard, 

 A. S. Hitchcock. 



Under the heading of brief notes W. L. McAtee 

 and Alex. Wetmore called attention to the presence 



