“My dear Sir,—I am quite ashamed of having delayed answering your letter, and thanking you for the communications you sent me for so long a time. In regard to the lamps, an account will be given of them in the Annales de Chimie for the next month. The lens is composed of pieces of glass forming a circle three feet in diameter, ground to three feet focal length. The lamp is similar to an Argand lamp, having hardly any other difference, except four concentric circular wicks instead of one. The external wick is about three inches in diameter. The light given by the lens is remarkably brilliant. When we were at Folkestone Hill, the lamp at Blancnez appeared to give about four times the light of the Dungeness Lighthouse, though the distance of the lamp was nearly double that of the lighthouse. The only difficulty which occurs to me in their employment in lighthouses is the small angle to which a single lens gives light. I think one lens is brilliant for seven degrees, and could not answer for more than eight or nine degrees.
“The Cordouan Lighthouse is to be fitted up with ten lenses round one lamp.
“With best wishes to Mrs. S. and your family, ever yours,
“Thos. Colby.”
The merits of the dioptric system of illumination were brought before the Commissioners of Northern Lighthouses in Mr. Stevenson’s Report of December 1821, and, as is well known, it has, with various extensions and important improvements, been very generally adopted in all cases where it is applicable to lighthouse illumination.
CHAPTER IV.
ROADS.
1798–1835.
Early roads and road-making—Edgeworth and M’Adam’s systems of roads—Stevenson’s system of roads—Cast-iron and stone tracks.
Writing at an early date, Mr. Stevenson has given the following sketch of Roads and Road-making:—
“In early periods, when every family formed a kind of community within itself for providing the necessaries of life, it is obvious that there could be little communication with distant parts of the country, and there was, therefore, no use for roads, which, long after the establishment of towns, must have continued in the state of footpaths and horse-tracks. The bulky articles of fuel and building materials are likely to have given rise to the first idea of a sledge, the precursor of the wheel-carriage, which ultimately led to the construction of anything like a regular path. The first roads of Britain appear to have been the Military Ways of the Romans. Some remains of these are still to be seen in various parts of the kingdom, and even in the immediate vicinity of the city of Edinburgh. It is, however, quite astonishing how slow the progress of improvement in road-making seems to have been, and especially its adaptation to economical purposes; although all classes must have felt an equal interest in the formation of roads, as both the landed proprietor and the citizen were to be mutually benefited by thus laying open the country. But it requires the accumulated wealth of ages to produce improvements so expensive. It is long before the mind can be brought to approve of any radical change of habit, however advantageous; and the scale adopted in the first instance is often so circumscribed, that the whole measure requires to be extended and even to be changed a second, and perhaps a third time, in keeping pace with the public demands for improvement.
“It is well known, that even so late as about the middle of the last century, almost the whole land carriage of Scotland, and a great part of England, was conducted upon horseback, the animals employed being termed pack-horses. To the horse-tracks thus produced, and which in the first instance were formed without regard to steep acclivities, are to be ascribed the evils which we now labour under, as attendant on the laying out of our roads for the modern improvement of wheel-carriages. Nor was it till after much practice and the application of scientific principles, long after the introduction of carriages, that we were induced to improve the line of draught and adopt level tracks of road, although perhaps more circuitous.
“In Great Britain the road department, after much experience, is now brought into a system by which the highways are made and upheld by dues directly levied on those who travel or use them,—excepting, indeed, such roads as are situated in very remote parts of the country, where the Government, with the most enlightened policy, has either executed the works directly by the troops upon the peace establishment, as in the case of General Wade’s army, or given aid towards the original formation of extensive lines of road, for opening the more remote districts of the country. There is, perhaps, no better criterion for judging of the prosperity of a country than by its public improvements; and were this subject considered in all its bearings, we should hardly be able to quote any stronger evidence of internal riches and true greatness, than we find connected with the subject of its public roads. It appears from a very general or cursory calculation, which the reporter has made, that the highways of Great Britain and Ireland, independently of the almost innumerable parish and private roads, extend to about 25,000 miles. The expense of these, including bridges, etc., on a very moderate calculation, may be stated throughout the kingdom at the rate of £800 per mile, which is equal to no less than the aggregate sum of twenty millions sterling. Now, to what branch of political economy can we look with more certainty and propriety than to such splendid examples of the substantial wealth and resources of a country? for until a kingdom is traversed and laid open by roads, its government must be weak, and its people remain in a state of comparative poverty.
“But in so extensive a concern as the system of roads, involving so great an expense, we may naturally look for small beginnings and very gradual advancement. Accordingly, we find in the first formation of highways, before their utility could be fully understood or experience had shown the benefits of science in the practice of the engineer, the early road-maker only increased the breadth of the horse-track, and strewed it over with gravel from the neighbouring brook. Indeed, we know that so late as the year 1542, even the streets of London were formed in this way; and it is said to be established by the records of Parliament, that when the new system of road-making was first proposed to be extended beyond the region of a few miles from that metropolis, such was the mistaken policy and narrow-minded views of the immediate proprietors, that the measure was strenuously opposed by those who wished to make a monopoly of the supplies for the metropolis, as detrimental to the established order of things.”