military
bridges with India-rubber pontoons, which was most fully described and
illustrated in the original memoir from which the volume now just
published has grown. He subsequently, as Professor of Practical
Engineering at the Military Academy, aided in developing and perfecting
the pontoon-drill,--a department in which G.W. Smith, McClellan, and
Duane ably and successfully labored.

We suppose that all profound and sincere students of military operations
are agreed in accepting bridge-trains and skilled pontoniers as among
the necessities of grand armies. In proportion as the campaigns which an
army is to make are to be conducted on theatres intersected by rivers
will be the importance of its bridge-service. Our own country, abounding
in rivers of the grandest proportions, will need to be always ready for
applying the highest skill and the best bridge-equipage in facilitating
such movements as may prove necessary. We accept this as an
indispensable part of our organized system of war-_materiel_. Were other
evidences lacking, the experiences of the Chickahominy, Rappahannock,
Potomac, and Tennessee will perpetually enforce the argument. The
generation which has fought the Battle of Fredericksburg, and which has
witnessed Lee's narrow escape near Williamsport, is sufficiently
instructed not to question the saving virtues and mobilizing influences
of bridge-trains.

The chief essentials in a military bridge-system are lightness, facility
of transportation, ease of manoeuvre in bridge-formation, stability,
security, and economy. It necessarily makes heavy demands for
transportation; and on this account bridge-trains have frequently been
left behind, when their retention would have proved of the utmost
importance. Their true use is to facilitate campaign-movements; and
while they should be taken only when there is a reasonable prospect of
their being real facilites, they should not be left behind when any such
prospect exists. It was in response to the demand for easy
transportation that the system for India-rubber pontoons was elaborated.
Single supporting cylinders of rubber-coated canvas were first
experimentally used in 1836 by Captain John F. Lane, United States army,
on the Tallapoosa and Chattahoochee Rivers in Alabama. The
service-pontoon, as arranged by General Cullum, is composed of three
connected cylinders of rubber-coated canvas, each having three
compartments. On these pontoons, when inflated, the bridge-