Every manufacturer is also aware that the difficulties encountered in manufactures are not limited to the substances employed, but extend to all the different {74} processes and stages of processes through which these substances have to pass, and to all the forces, tools, machinery, and appliances employed in those processes; in the manufacture of glass, for example, the greatest care has to be exercised in the making and gradual heating of the pots in which the glass is melted, the proportions of the materials, the construction of the furnaces, the management of the heat, and a whole host of minor conditions too numerous to mention, all of which must be attended to with the greatest care. In the manufacture of iron and steel, the smelting of copper, the refining of nickel, the preparation and baking of porcelain, and in many other trades, innumerable difficulties, all having their origin in the properties of matter and forces, continually beset the manufacturers. In some cases difficulties occur which perplex both the workman and the scientific man called in to his aid, and so far from an unscientific workman being able to overcome them, even with the aid of the scientific man, he is unable to do so. The hidden difficulties which beset a manufacturer are not unfrequently so inscrutable that the present state of knowledge in science fails to explain them. Who can tell why it is that wire-work of brass or German silver becomes gradually brittle by lapse of time? Or why varnish made in the open country has different properties from that made in a town? Or why silk dyed in Lyons should possess a finer colour than the same silk dyed by the same process in Coventry? {75} With our present extremely imperfect knowledge of Physical and Chemical science, we can perhaps hardly form an idea of the amount of knowledge yet to be discovered respecting the phenomena which manufactures present. One of the inevitable results of these difficulties in manufacturing processes and of deficiency of knowledge, is the production of a large amount of goods of an inferior quality; and useless goods, technically called "wasters," the cost of which has to be laid upon the saleable ones, and thus the price of the latter is enhanced to the consumer. For instance, flint glass discoloured by iron has sometimes to be sold at a loss for making common enamel; waste window glass has to be sold as "rockery" for ornamenting gardens, and defective articles of glass or metal have to be re-melted. In consequence of this want of new knowledge, manufacturers continue to suffer losses which might be avoided; high prices of useful articles are maintained; defects in their quality are not improved; preventable accidents still continue to happen; the health of workmen continues to suffer; many means of curing diseases remain unknown; medical practice remains full of empiricism, &c., &c.