4.See above ch.II, sec.1.In April 1894, for instance, six plovers' eggs, the first of the season, were sold in London at 10s.6d each.The following day there were more, and the price fell to 5s.; the next day to 3s.each; and a week later to 4d.
5.This estimate is commonly attributed to Gregory King.Its bearing on the law of demand is admirably discussed by Lord Lauderdale (Inquiry, pp.51-3).It is represented in fig.(8) by the curve DD', the point A corresponding to the ordinary price.
If we take account of the fact that where the price of wheat is very low, it may be used, as it was for instance in 1834, for feeding cattle and sheep and pigs and for brewing and distilling, the lower part of the curve would take a shape somewhat like that of the dotted line in the figure.And if we assume that when the price is very high, cheaper substitutes can be got for it, the upper part of the curve would take a shape similar to that of the upper dotted line.
6.Chronicon Preciosum (A.D.1745) says that the price of wheat in London was as low as 2s.a quarter in 1336: and that at Leicester it sold at 40s.on a Saturday, and at 14s.on the following Friday.
7.Thus the general demand of any one person for such a thing as water is the aggregate (or compound, see V, VI, 3) of his demand for it for each use; in the same way as the demand of a group of people of different orders of wealth for a commodity, which is serviceable in only one use, is the aggregate of the demands of each member of the group.Again, just as the demand of the rich for peas is considerable even at a very high price, but loses all elasticity at a price that is still high relatively to the consumption of the poor; so the demand of the individual for water to drink is considerable even at a very high price, but loses all elasticity at a price that is still high relatively to his demand for it for the purpose of cleaning up the house.And as the aggregate of a number of demands on the part of different classes of people for peas retains elasticity over a larger range of price than will that of any one individual, so the demand of an individual for water for many uses retains elasticity over a larger range of prices than his demand for it for any one use.
Compare an article by J.B.Clark on A Universal Law of Economic Variation in the Harvard Journal of Economics, Vol.VIII.
8.When a statistical table shows the gradual growth of the consumption of a commodity over a long series of years, we may want to compare the percentage by which it increases in different years.This can be done pretty easily with a little practice.But when the figures are expressed in the form of a statistical diagram, it cannot easily be done, without translating the diagram back into figures; and this is a cause of the disfavour in which many statisticians hold the graphic method.But by the knowledge of one simple rule the balance can be turned, so far as this point goes, in favour of the graphic method.The rule is as follows: - Let the quantity of a commodity consumed (or of trade carried, or of tax levied etc.) be measured by horizontal lines parallel to Ox, fig.(9), while the corresponding years are in the usual manner ticked off in descending order at equal distances along Oy.To measure the rate of growth at any point P, put a ruler to touch the curve at P.Let it meet Oy in t, and let N be the point on Oy at the same vertical height as P: then the number of years marked off along Oy by the distance Nt is the inverse of the fraction by which the amount is increasing annually.That is, if Nt is 20 years, the amount is increasing at the rate of 1/20, i.e.of 5 per cent, annually.if Nt is 25years, the increase is 1/25 or 4 per cent annually; and so on.
