8 On Roads and Wheel-Carriages. 
than oil, When grease of any kind is in too liquid a state for 
preventing friction, it may be improved by adding the powder of 
any mineral that soils easily, such as black-lead, &c. 
On the preceding principles the durability of bodies exposed 
to friction might be easily ascertained. When the surfaces are 
of the same kind, the durability will be inversely as the indenta- 
tion, and consequently inversely as the extensibility. When the 
surfaces are of different kinds, the durability will be inversely as 
the extensibility of the harder surface. 
It is obvious that when bodies roll, different laws will obtain ; 
but the subject might be treated in a similar manner, which will 
be considered at some future period. 
Tuomas TREDGOLD. 
Il. On Roads and Wheel-Carriages. By Mr. BensAMiN 
WINGROVE. 
Tuar important branch of our political ceconomy, the manage- 
ment of the public roads, whether considered in reference to con- 
venience or burthen, forms an object of such consequence to the 
community at large, and to the agricultural interests in particu- 
lar, that I think no apology necessary for intruding on the public 
a communication on that subject. 
The vast increase of the commerce and wealth of this country 
has long demanded the convenience and luxury of good roads ; 
and the whole art necessary for their construction and preserva- 
tion has. been, for many years past, imparted to the publie by 
various treatises and essays, which are to be found in the libraries 
of every establishment for the advancement of science and know- 
ledge. Our enlightened legislature has too, by various general and 
local statutes, furnished all the requisite powers and authorities 
for effecting so important a design. Yet, notwithstanding a call 
so imperious, information so adequate, and power so efficient, a 
supineness truly unaccountable has, till within a few years past, 
prevailed throughout the country on this interesting subject. I 
might indeed aver that, in some parts, the system has been alto- 
gether retrograde. ‘The inconveniences which have resulted from 
this great popular neglect, have however, at last, proved insup- 
portable; and in consequence the reformation of the road system 
has commenced with a zeal and energy that cannot fail to pro- 
duce the most successful issue. 
In the northern counties, particularly in Yorkshire and Not- 
tinghamshire, and in some parts about London, (in all which 
Mr. Clay has successfully introduced his ingenious machinery, 
improvements have been effected. In this part of the kingdom, 
the 
