We have recently seen the Freeborn, the Pawnee, and the Harriet Lane, when assailing the rebel batteries on the James and the Potomac, compelled to take positions at the distance of two miles, and to keep constantly moving, and compelled consequently to throw away most of their costly ammunition in uncertain shots, at the same time that they were constantly exposed to shots which might destroy their engines and explode their boilers.  There was no lack of courage on the part of their gallant officers; but, from the insufficiency of the vessels, they were obliged to use a wise discretion, and to take all reasonable precautions for the safety of their ships, so important and yet so inadequate to the service of the country.  And when Fort Sumter was about to fall, and when a single shot-proof gun-boat could have defied the rebel batteries, and without the loss of a man have conveyed to the fortress stores for six months and a whole battalion of troops, that single gun-boat,—­a mere gun-boat, which need not have passed within one thousand yards of any batteries on her way,—­could not be commanded by the Government, and the gallant Anderson was compelled to lower to treason that flag whose fall has aroused the nation to arms.

The earliest experiments upon the power of iron plate to resist the force of cannon-balls appear to have been made in France by M. de Montgery, an officer in the French navy, as far back as 1810.  He proposed to cover the sides of ships with several plates of iron, of the aggregate thickness of four inches, which he alleged would resist the force of any projectile.  But Napoleon had not confidence in his navy; he had lost the battles of the Nile and Trafalgar; ever successful on the land, his ships had been swept by Nelson from the deep; and he had neither time nor disposition to investigate new plans for the restoration of the navy, or even to take up Fulton’s new discovery.  It was reserved for the third Napoleon to develop the original idea of a Frenchman, and thus to place France on the sea nearly or quite upon a footing with England.

Some twelve years later, General Paixhans, who gave his name to the large guns of modern times, (although their prior invention was claimed by the late Colonel Bomford,) again commended plate-armor for ships to his Government; but his advice was not then adopted.

With the improvement of cannon the importance of plate-armor became more and more apparent; and at length Mr. Stevens, under the sanction of our Government, instituted a series of experiments upon iron plates, and soon after commenced building an immense floating battery for the defence of New York, at Hoboken, which is still unfinished, but which, it is rumored, will, if Congress appropriates the means, be completed the present season.

Stevens was the first to carry out the idea of a mail-clad steamer; and it is alone due to the apathy of the late Administration, which has neglected our navy while indulging in its Southern proclivities, that our nation has not the honor of launching the first steamer in a coat-of-mail.  The frame, however, of such a vessel has been long in place, the hull is nearly complete, the engines are far advanced, and the finishing stroke may soon be given.