How wonderfully beneficial to mankind is this beautiful arrangement of the metallic fibrous system! Without it what could we do? our manufactures would be confined to simple castings, or crystallizations, possessed merely of strength in proportion to the cohesive nature of the metal. Where would be all the wonderful springs whose fineness vies with the silken fibre? Of what could they be constructed? All-powerful gold would not suffice, nor silver; though each, in its place, possesses wonderful properties. Gold and silver may both be spread in the thinnest conceivable coat over space incredible; on the gilded cup, or, still thinner by electric agency, on the plated epergne. But iron alone is to the arts, the “_summum bonum_” for which there is no substitute: it is the “_sine quâ non_” of practical mechanics. Improvements in the manufacture of a very superior iron may, we believe, be placed to the credit of the gunmaking profession exclusively; no other body or class of men having ever yet deemed it worth their trouble to endeavour to obtain anything of a better description _than bar iron, suitable to make steel from_. Mr. Mushet, from whose work I have already quoted, has evidently been more intimately acquainted with the routine of iron manufacturing than any other person I ever met with or read of: he understands the question perfectly; yet he seems to care for nothing further _than a suitable steel iron_. How many and how fearful have been the explosions by all-powerful steam since the period of its introduction. How many weeping widows, and how many fatherless children have had to mourn its effects! Yet what has human ingenuity done, what have the wonderful energies of the present race of scientific men accomplished to stay this annual slaughter? Comparatively little beyond discovery of mysterious causes where none exist. It reminds me of my first lesson in coursing--“If you want to find a hare, young man,” said the keeper, “look at your feet: you will not find her at a distance.” So it is with the state of knowledge on steam boiler explosions; if you want to find the cause, look “at your feet:” do not endeavour to envelope in mystery, what you may find in simple and natural causes.