(3) The relations between one of the great arterial industries, such as coal-mining, railway transport, or machine-making, and a specific manufacture may be regarded as auxiliary. The extent to which the price of coal, railway rates, etc., enters into the price of the goods and affects the condition of profits in the trade measures the closeness of this auxiliary connection. In the case of the smelting industries or in the steam transport trades, even in the pottery trades, the part played by coal is so important that the relation is rather that of a primary than an auxiliary connection--_i.e._, coal-mining must be ranked as co-ordinate to smelting. But where heat is not the direct agent of manufacture, but is required to furnish steam-motor alone, as in the textile factories, the connection may be termed auxiliary. (4) The relationship between some industries is "sympathetic" in the sense that the commodities they produce appeal to closely related tastes, or are members of a group whose consumption is related harmoniously. In foods we have the relations between bread, butter, and cheese; the relation in which sugar and salt stand to a large number of consumables. Some of these are natural relations in the sense that one supplies a corrective to some defect of the other, or that the combination enhances the satisfaction or advantage which would accrue from the consumption of each severally. In other cases the connection is more conventional, as that between alcohol and tobacco. The sporting tastes of man supply a strong sympathetic bond between many trades. The same is true of literary, artistic, or other tastes, which by the simultaneous demand which they make upon several industries, in some proportion determined by the harmonious satisfaction of their desires, throw these industries into sympathetic groups.[114] These four bonds mark an identity of interest between different industries.