123 NATURE 
[APRIL 4, Ton 
his horse and carriage, and more expeditiously com- | 
pleting the new surtace, it was not possible to pro- 
vide a closely fitted road, which should have its inter- 
stices filled up by the chip and grit from the stones 
themselves, and which was an essential desideratum 
according to the Macadam theory. His principle was 
that no water should enter the surface of the road or 
penetrate beneath the crust. To keep water out of 
the road was one of the most essential points, if it 
was to be efficient. He strongly condemned any 
insertion of loose material into the interstices of the 
metal, or allowing water to enter between the stones 
of the crust. These maxims of Macadam came to be 
disregarded when steam rolling was _ introduced. 
When rolling was to be done in one operation, a 
device had to be resorted to, that the spaces between 
the stones might be closed by added packing, and 
this has been done by making what can only be 
described as a soup of dirt and water and pouring it 
upon the stones and brushing and rolling this liquid 
mud into the crust of the road. The road thus when 
opened for use is crusted with a coating of stones, 
the only binding of which is water thickened with dirt, 
or perhaps dirt diluted with water is the proper descrip- 
tion. The result is that it can never be a good road 
in wet weather, and can never be a good road in dry 
weather. As long as it is in a slightly damp state, 
and not subjected to severe wet weather or long- 
continued drought, it may be a fairly good road. In 
wet weather water can get in where it has come out, 
reproducing the mud soup, and the traffic squeezes 
it up and out of the road. In dry weather, the bind- 
ing being reduced in bulk and loosened by the 
evaporation of the moisture which gave the inserted 
dirt.some cohesion, the stones move and are picked 
out of the surface, and so holes are left for the water 
to lodge in the dirt below when again rain begins 
to fall. What would Macadam say, if he could visit 
the scene of his scientific labours, to hear the phrase 
*‘ water binding ’’ used to describe the means employed 
for consolidating the crust. To call a water-formed 
road a macadamised road is a contradiction in terms. 
His emphatic declaration was: ‘‘ Every road is to be 
made of broken stones, without mixture of earth, 
clay, chalk, or any other matter that will imbibe 
water.” 
But further, the road roller has not in another 
aspect proved to be an unmixed blessing. For it is 
not uncommon to see that its use has developed 
another evil. The heavy road roller coming on to a 
layer of stones, surrounded with liquid and therefore 
non-resisting mud, and pressing down the stones by 
its weight, necessarily must move the water and the 
dirt in suspension, otherwise the stones would not 
go close together. The liquid is therefore squeezed 
out of the way, and as the great width of the roller 
prevents its escape sideways, except at the edges, it 
must go forwards, and (water being practically incom- 
pressible) forces the water and the dirt and the stones 
in front upwards, forming a ridge in front. The roller 
advances, and when it cannot force the ridge farther 
forward, it then mounts it and descends in front, and 
so da capo, with the consequence that the road 
becomes a series of ridges and furrows, and when 
drying up resembles a mackerel’s side, a series of 
darlx-toned wet hollows and light-toned dry mounds. 
No worse state of matters for the traveller and his 
vehicle, or for durability of the road surface, can be 
conceived. 
Tue Future. 
What is the road of the future to be?. It is a 
question which all who are associated with the 
management of roads have come to see calls impera- 
tively for an answer. The problem is to find the 
NO. 2214, VOL. 89] 
best mode by which a road can be constructed, which’ 
| will not have its surface broken by traffic, and will 
make transit easier both for passengers and goods, 
and shall neither form puddle holes nor exude mud 
to clog the vehicles and to form thick dust when the 
weather is dry; in short, that there shall be no loose 
material from the road, except the small quantity 
caused by surface wear, which it is found is but 
trifling when a sound crust has been rolled in. That 
such a road can be laid anyone may see by paying a 
visit to the Thames Embankment, the traffic on 
which was small formerly, the road being shunned 
as one of the worst in the country, but which is now 
used by an enormous number of vehicles, often as 
many as 1600 in an hour. It will be seen there that 
water on the surface dries off very quickly, there 
being no mass of mud to hold it, and that in the 
driest weather there is practically no dust. No water- 
ing is done during the day, the surface receiving one 
washing during the night, because of the horse traffic. 
But there is no need for the use of water carts by 
day. Even during the long drought of 1911 there 
was no watering, yet there was no appreciable dust. 
The necessity for the development of road improve- 
ment as a matter of national concern is now recog- 
nised, and this has led to the establishment of the 
Road Board, as a Government department, to the 
charge of which the money raised by taxation of 
motor vehicles and motor fuel is handed over -to be 
administered in aid of road improvement. 
The Board encourages road improvement by giving 
grants in aid to those road authorities who undertake 
works of improvement in their districts.: The Board 
has also been conducting, and will continue to 
conduct through their engineer and technical advisers, 
experiments, both in the laboratory and on the road 
itself. 
I shall conclude by directing your attention to some 
of the results of recent experiments, by which I thinls 
you will see that it has been possible for the Board 
with the aid of its staff, and the experience of 
numerous surveyors who have been experimenting for 
many years, to obtain valuable and practical informa- 
tion, as regards the choice of material, its manipu- 
lation, its proportions, and the mode of laying it, 
which may ensure that good roads can be made, 
roads which will keep their surface sound for twice 
as long as the water-bound macadam road, and will 
not become uneven and break into holes, which was 
the fate of all the roads of the past. 
The question: ‘‘What shall be the weight-bearing 
crust?’ is one of vast importance, and this is engag- 
ing the attention of the advisers to the Road Board. 
I do not intend to dogmatise on the subject, but only 
to show you what steps of progress are being made, 
what has already been consummated in the production 
of roads which are to the old water-bound macadam 
what the genuine macadam was to the. old track of 
foot-deep mud and bulky stones. One thing is now 
universally recognised, that the road of the future 
shall be a truly bound road, in which, whatever kind 
of stone is used—a matter into which there is not 
time to enter—that stone shall be held together by 
some pitchy or bituminous material, so that it shall 
be indeed a crust and not something which has no 
real cohesion, and into which Macadam’s enemy, the 
water, can make its way whenever water falls. That 
this result has been attained in a practical wav is 
manifest from the pieces of road crust cut out after 
they have been under traffic for long periods. 
Roads formed as regards the crust in this way are 
now common. Many can be seen in Kent and other 
counties near London, and stretches are being laid 
throughout the kingdom. Great success was attained 
