September 14, 1905] 



NA TURE 



487 



will be carried out on these lines, for the results seem 

 rather contradictory, and there are probably a good 

 many factors to be observed. 



In the methods so far referred to, attempts are 

 made to improve the roads with their present mode 

 of construction. But it would be more rational to 

 use materials in road-making that would not give 

 rise to dust ; for example, with materials of a viscous 

 nature. Tar very naturally suggests itself, and a 

 good many experiments have been made either by 

 mixing it with road materials or by applying it hot 

 as a coating. Mr. Scott Montagu, in a paper recently 

 read before the Automobile Club, gives several 

 instances in which the tarring of roads has proved 

 effective. It is perhaps a little early to say whether 

 this treatment remains satisfactory under all con- 

 ditions, or whether it may after a time give rise to 

 unpleasant mud in wet weather under certain con- 

 ditions. 



In order to obtain a permanent result it seems 

 necessary that the crust of the roadway should be 

 really waterproof to a fair depth, so that dust-forming 

 materials cannot work up. This result can only be 

 obtained bv combining the tar with the materials 



yet such measures can be taken only over a small 

 proportion of our roads owing to the cost. In towns 

 and large villages the roads might be suitably treated ; 

 but the average motorist seeks the country', and the 

 greater part of the routes which he wishes to traverse 

 will not pay for any special treatment. It therefore 

 becomes very important to modify the design of cars 

 so that the dust raised may be reduced to a minimum, 

 and also, if possible, to find some simple means of 

 checking the dust in the case of cars already in use. 



One of the simplest defects to remedy is the direc- 

 tion of the exhaust, which is sometimes pointed down- 

 wards. In such a case the dust raised by the exhaust 

 alone may be considerable, and an improvement may 

 be made very simply. It has even been proposed to 

 use the exhaust, suitably directed, for laying the dust 

 which is otherwise raised by the car; and M. Baudry 

 de Saunier, editor of ha Vie Automobile, vouches 

 for the efficiency of the Feugere system, as it is called. 

 The exhaust is discharged from a horizontal pipe 

 taken across the back of the car, having a line of 

 holes along its length. Thus a number of jets in 

 the same plane is formed, and the pipe is so mounted 

 that the angle at which these jets im])inge on the 



F:G. 2. — Test of a dusty ( 



■ flour at the Crystal Pala 



I the Aittoiitobile Club J o^ 



used in construction. It is useless, however, to tar 

 such materials as granite or syenite, because the tar 

 remains only on the outside, and as the material is 

 worn the tar becomes ineffective. For that reason 

 Mr. E. P. Hooley uses furnace slag, which is very 

 porous, and produces a material which he has named 

 " Tarmac." The slag is taken hot from the furnaces, 

 broken, and thrown into tanks of tar. Upon cooling, 

 the tar becomes absorbed, and the slag is thoroughly 

 impregnated, so that if the pieces are broken further 

 a tarred surface is still found. In other words, the 

 material is such that it cannot give rise to dust. It 

 is used in construction, like other materials, to a 

 depth of several inches. The initial cost is rather 

 heavier than for a macadam road, but this appears 

 to be more than counterbalanced by the greater 

 durability and the fact that a waterproof road is 

 obtained free from dust and requiring much less 

 cleaning than the usual macadam. 



(2) Design of the Car. 



Although a permanently good road may be made 

 by the use of such materials as Tarmac, and dusty 

 roads may be cured temporarily by various means, 



NO 1S72, VOL. 72] 



roadway may be varied so as to be as effective as 

 possible. Naturally, the less fluctuating the stream 

 of exhaust gases the better for such a purpose, and 

 the result is said to have been much more satisfactory 

 on a four-cylinder than on a single-cylinder car. I 

 have not had an opportunity of seeing this device 

 in action. 



Speaking generally, and leaving such special points 

 as direction of exhaust out of account, it may be said 

 that the dust is raised by the tyres, and is then 

 scattered by the air currents produced by the body. 

 In other words, if the body were moved along the 

 road at its normal height, supported by other means 

 than the wheels, very little dust would result. But 

 it is equally true that if the wheels could be run 

 without the body there would not be much cause for 

 complaint as to dust. By body is here meant the 

 whole structure, apart from the wheels, so that the 

 term is more comprehensive than usual. The 

 passage of a car body through the air necessarily 

 creates a great deal of disturbance, and the extent 

 to w;hich the air near the ground is disturbed must 

 depend to a great extent upon the shape of the body. 

 The less the disturbance, the less will the dust be 

 formed into a cloud. 



