第44章

Some instruments, without the intervention either of labor or of other instruments, produce events which directly supply our wants.Thus a peach tree yields its fruit to our hand.The operation of others only tends to the production of events supplying our wants.The growth of a crop of wheat is only a step towards the production of bread.Others require the help of either labor, or some other instrument.A row boat is useless without the labor of the man who plies the oar; a carriage, without the cooperation of the horses who draw it.All instruments, however, either produce, or contribute to the production, of events supplying some of our wants.Their power to produce such events, or the amount of them that they do produce, may be termed their capacity.

It is necessary to have some common measure for the purpose of comparing the capacity of instruments or the returns that are made by them, with the labor or its equivalents that went to form them.For this purpose, also, labor will be adopted, and the events brought to pass by any instrument will be estimated by the amount of labor to which they are esteemed equivalent by the owner of the instrument.As we proceed, it will appear, that this use of the term has no other effect than that of giving distinctness to our nomenclature.Besides, it often really happens, that the returns made by instruments, directly compare with labor, because they directly save labor.For instance, wooden or metal pipes are occasionally used to conduct water from a spring to some dwelling-house.Were they not there, the water would have to be carried within the dwelling by some of the domestics, and therefore the instrument formed by the pipes may be said indifferently, either to supply a certain amount of water, or save a certain portion of labor.

With one considerable exception, afterwards to be noted, all instruments at length bring to pass, or aid in bringing to pass, all the events which they can bring, or can help to bring to pass, I shall use the term exhaustion, to denote this passage of things from the class of instruments, into things which are not instruments.When an instrument is said to be exhausted, it is meant that the matters of which it was composed have passed out of the class of instruments into that of materials.

Sometimes they pass from the one class to the other suddenly.Thus, articles used for food and fuel, bring to pass all the events for which they were formed, very shortly.The appetite of hunger is gratified, and beat is communicated to the frame, in a few minutes, and the faggot and the bread, having yielded all the nourishment and heat stored up in them, then cease to be instruments.Gunpowder brings certain events to an issue instantaneously.The bullet is discharged, and the rock split, in an instant.

This sudden and complete exhaustion of the capacity of instruments is what is usually termed consumption.Sometimes the matters of which instruments are formed pass from the class of instruments to that of materials by degrees.

Thus tools and articles of wearing apparel are in use for a long time before they cease to be instruments.A saw may be in employment for years; a hat defends the head for months.When the capacity of instruments is thus gradually exhausted, it is usually said that they are worn out, and this sort 6f exhaustion is termed wear.

Sometimes the capacity of instruments is accidentally done away with, and they consequently pass out of the class of instruments, without being exhausted.Thus a house may be burned, cloth may be eaten by vermin.They are then said to be destroyed.A partial degree of this is damage.In calculating the capacity of instruments, it is necessary to reckon the risk they run of destruction or damage.In any estimation of the capacity, for instance, of a crop of wheat, we have to make as accurate an allowance as may be, for the risk of its destruction or damage, by the inclemency of the weather or other accidents, before the harvesting of it be accomplished.

3.Between the formation and exhaustion of instruments a space of time intervenes.This necessarily happens because all events take place in time.

Sometimes that space extends to years, sometimes to months, occasionally to shorter periods, but it always exists.

The circumstances we have hitherto assumed as common to all instruments, and the events they generate, will, I believe, on examination, be found actually to be so.There is one circumstance, however, which it is necessary to assume as common to them all, and which in reality is not altogether so.In comparing the capacity of two or more instruments, which supply, or tend to supply, wants of the same sort, we may very often measure them by the relative physical effects, resulting from the action of the events brought to pass by them.Thus, if the consumption of one cord of fire wood, of a particular sort, is capable of producing exactly double the heat which the consumption of another cord of another sort produces, a cord of the former, will have double the capacity of a cord of the latter, and, if the one be equivalent to four, the other will be equivalent to exactly two days labor.In the same way, a log of timber from ]Norway, about to be employed in the construction of a house, if of equal size, strength, and durability, with another from Prussia, may, with justice be considered as of equal capacity to it; and so of many other instruments.We shall see afterwards, however, that this mode of determining the capacity of similar instruments, is in many cases incorrect, and that the instances are very numerous, where the relative capacities of instruments of the same sort, depend on other causes than their mere physical properties.