and as he sees the work and its conditions they need not be, within his control in anything like the fashion in which he controls his tools and the materials employed in his manual operations; they work well or ill, and what comes of it is in some degree a matter of his fortune of success or failure, such as comes to the man who has done his best under Providence. In case of a striking outcome for good or ill from the operation of such natural processes the devout craftsman is inclined to rate it as the act of God; very much as does the devout husbandman who depends on rain rather than on irrigation. It is the part of the wise workman in such a case to take what comes, without elation or repining, in so far as these factors of success and failure are not comprised in his presumed workmanlike proficiency. The matter lies differently in the machine industry. The mechanical processes here engaged are calculable, measurable, and contain no mysterious element of providential ambiguity. In proportion as they work to the best effect, they are capable of theoretical statement, not merely approachable by rule of thumb. The designing engineer takes his measures on the basis of ascertained quantitative fact. He knows the forces employed, and, indeed, he can employ only such as he knows and only so far as he knows them; and he arranges for the processes that are to do the work, with only such calculable margin of error as is due to the ascertained average infirmity of the available materials. He deals with forces and effects standardised in the same opaque terms. He will be proficient in his craft in much the same degree in which he is master of the matter-of-fact logic involved in mechanical processes of pressure, velocity, displacement and the like; not in proportion as he can adroitly impart to the available materials the workmanlike turn of his own manual force and dexterity, nor in the degree in which he may be able shrewdly to guess the run of the season or the variations of temperature and moisture that condition the effectual serviceability of natural processes in handicraft.