This passage will be rapid, or slow, as the amount of knowledge possessed is small, or great.When art is in its infancy, and men know but a few of the properties fitting them for becoming instruments, that are inherent in the materials in their possession, they cannot much vary their mode of proceeding on them, by combining, and giving new turns to their actions on each other.In more advanced stages of society, on the contrary, where the powers of a great number of materials are known, arm where consequently their operations on each other, may be combined, and multiplied to a great extent, the means by which the same end may be attained are very numerous.
Some of them are more easy or expeditious than others, but they differ by very slight degrees, and the instruments formed by successively adopting them, would occupy positions in one series not widely distant from one another.
If we then consider the capacity that may be given any amount of materials, by a society among whom the progress of art is stationary, as separated into the durability, and efficiency, of the instruments its members form, it would appear, that they are both subject to similar laws, and that neither can be indefinitely increased, without carrying the instruments constructed continually on, to orders of slower return.The same general conclusions must obviously hold good.concerning the capacity considered as combined of both.There is, however, a circumstance flowing from the consideration of this union, which is deserving of notice, as it has considerable effect in the relations between the cost and capacity of instruments, and, consequently, on the position to be assigned them.It often happens, that additional labor bestowed on an instrument, to give it greater efficiency, gives it also greater durability.Thus the same choice of materials, and the same careful and laborious formation of them, that render the walls of a dwelling-house effective in excluding the inclemency of the weather, give it also solidity and strength, and consequently prolong its duration.A tool, in the fabrication of which good steel has been employed, not only cuts better, but lasts longer, than one formed of inferior stuff.In such cases, and they are very numerous, the capacity being increased, both as concerns durability and efficiency, by the same outlay, its proportion to the cost is greater and a larger expenditure may be made on the formation of the instrument without moving it at all or moving it but a short distance towards the orders of slower return.Sometimes the same expenditure that gives efficiency to instruments, partly also increases their durability and partly, quickens their exhaustion.Thus, the majority of roads in North America, and in many other countries, are constructed altogether of the soil of which the surface happens to consist, arranged in a form adapted to the purpose.
Such roads, unless in the best of weather, are very inefficient instruments in facilitating transport, and their durability is so small, that they are probably reconstructed, by repair, every four or five years.A road formed of small fragments of stone, in the manner that is termed macadtxraization, costs perhaps twenty times as much, but is both a far more efficient, and a far more durable instrument.Besides however being more durable, and efficient, the facility it gives to transport occasions an increase of transport, and its exhaustion is thus quickened.For example, the capacity of a road of this sort, may be adequate to the transport of two hundred thousand carriages; if this be spread over twenty years, it will be an instrument of much slower return, than if, in consequence of the annual transport being doubled, that number pass over it in ten years.
As efficiency and durability are frequently produced by the same means, so, it sometimes happens, that the means which would add to the one, cannot be employed, without diminishing the other.Thus there are many tools and utensils, that cannot be made very strong, and therefore durable, without being at the same time clumsy, and inefficient; and they cannot be made very light, and easy to work with, without being also of little durability.
The difficulty in the combination of the qualities of durability and efficiency, in the same materials, can only, however be considered as absolutely limiting the capacity of those instruments, to support the weight of which, a corporeal exertion is required; and is consequently confined to wearing apparel, and to those tools, and utensils, which are altogether moved by the hand.
When the weight rests on some firm basis, it can be poised, and by the application of sufficient expenditure friction, can be removed.The circumstance of the qualities of durability, and efficiency, depending on the same materials, has therefore, probably, on the whole, the effect of retarding somewhat, though not very greatly, the progress of instruments as greater capacity is given to them, towards the more slowly returning orders.
