In the field, this material is not less strikingly useful.  During this war, armies have marched through ten days of rain, and slept through as many rainy nights, and come out dry into the returning sunshine, with its artillery untarnished and its ammunition uninjured, because men and munitions were all under India-rubber.  When Goodyear’s ideas are carried out, it will be by pontoons of inflated India-rubber that rivers will be crossed.  A pontoon-train will then consist of one wagon drawn by two mules; and if the march is through a country that furnishes the wooden part of the bridge, a man may carry a pontoon on his back in addition to his knapsack and blanket.

In the naval service we meet this material in a form that attracts little attention, though it serves a purpose of perhaps unequalled utility.  Mechanics are aware, that, from the time of James Watt to the year 1850, the grand desideratum of the engine builder was a perfect joint,—­a joint that would not admit the escape of steam.  A steam-engine is all over joints and valves, from most of which some steam sooner or later would escape, since an engine in motion produces a continual jar that finally impaired the best joint that art could make.  The old joint-making process was exceedingly expensive.  The two surfaces of iron had to be most carefully ground and polished, then screwed together, and the edges closed with white lead.  By the use of a thin sheet of vulcanized India-rubber, placed between the iron surfaces, not only is all this expense saved, but a joint is produced that is absolutely and permanently perfect.  It is not even necessary to rub off the roughness of the casting, for the rougher the surface, the better the joint.  Goodyear’s invention supplies an article that Watt and Fulton sought in vain, and which would seem to put the finishing touch to the steam-engine,—­if, in these days of improvement, anything whatever could be considered finished.  At present, all engines are provided with these joints and valves, which save steam, diminish jar, and facilitate the separation of the parts.  It is difficult to compute the value of this improvement, in money.  We are informed, however, by competent authority, that a steamer of two thousand tons saves ten thousand dollars a year by its use.  Such is the demand for the engine-packing, as it is termed, that the owners of the factory where it is chiefly made, after constructing the largest water-wheel in the world, found it insufficient for their growing business, and were obliged to add to it a steam-engine of two hundred horse-power.  The New York agent of this company sells about a million dollars’ worth of packing per annum.