[43] The coin called a guinea is now no longer in use, but the name is still given, from custom, to 21 shillings. The pound, which was not a coin, but a note promising to pay 20 shillings to the bearer, is also disused for the present, and the sovereign supplies its place; but the name pound is still given to 20 shillings.
[44] Farthings are never written but as parts of a penny. Thus, three farthings being ¾ of a penny, is written ¾, or ¾. One halfpenny may be written either as 2/4 or ½; the latter is most common.
[45] When a decimal follows a whole number, the decimal is always of the same unit as the whole number. Thus, 5ᔆ·5 is five seconds and five-tenths of a second. Thus, 0ᔆ·5 means five-tenths of a second; 0ʰ·3, three-tenths of an hour.
[46] Before reading this article and the next, articles (29) and (42) should be read again carefully.
[47] Any fraction of a unit, whose numerator is unity, is generally called an aliquot part of that unit. Thus, 2s. and 10s. are both aliquot parts of a pound, being £⅒ and £½.
[48] A parallelepiped, or more properly, a rectangular parallelepiped, is a figure of the form of a brick; its sides, however, may be of any length; thus, the figure of a plank has the same name. A cube is a parallelepiped with equal sides, such as is a die.
[49] This generally comes in the same member of the sentence. In some cases the ingenuity of the student must be employed in detecting it. The reasoning of (238) is the best guide. The following may be very often applied. If it be evident that the answer must be less than the given quantity of its kind, multiply that given quantity by the less of the other two; if greater, by the greater. Thus, in the first question, 156 yards must cost more than 22; multiply, therefore, by 156.
[50] It is usual to place points, in the manner here shewn, between the quantities. Those who have read Section VIII. will see that the Rule of Three is no more than the process for finding the fourth term of a proportion from the other three.
[51] Commission is what is allowed by one merchant to another for buying or selling goods for him, and is usually a per-centage on the whole sum employed. Brokerage is an allowance similar to commission, under a different name, principally used in the buying and selling of stock in the funds.
Insurance is a per-centage paid to those who engage to make good to the payers any loss they may sustain by accidents from fire, or storms, according to the agreement, up to a certain amount which is named, and is a per-centage upon this amount. Tare, tret, and cloff, are allowances made in selling goods by wholesale, for the weight of the boxes or barrels which contain them, waste, &c.; and are usually either the price of a certain number of pounds of the goods for each box or barrel, or a certain allowance on each cwt.