his progress may be so retarded by dummies or sham mines as almost literally to compel him to dig his way.
"The power to telegraph through these torpedoes is of little consequence, inasmuch as there need be but one station and one operator. Using the testing-fuse manufactured by Abel, and a weak voltaic current, the operator can at any time satisfy himself as to continuity. Thus bridges and gulfs or breaks are not required for the land as they are in sea-mining. Ebonite has the further advantage on land that it takes but a single wire.
"Forts may be protected against assault, and your own rifle-pits from occupation by an enemy, simply by a proper distribution of these new engines of war. They may be planted line within line, and one row above another, and so arranged that volcanoes may be sprung at will under the feet of assaulting columns.
"The only attempt that was made in the late American war to bring the electrical torpedo into play on the land, was made by the Confederates at Port Fisher, in 1865, just before its fall. The narrow land-spit over which the attacking party had to advance was mined. The officer in charge used the magneto exploder.
"But the mines would not go off, owing no doubt to defective arrangements, for the instrument was new to him, and he had not been posted up as to the virtues of the ladder-circuit. The instrument used on this occasion was just such a one as this before you. It was the first that had reached the Confederacy. Here is then a most striking illustration of the importance of previous study and drill in this new and important arm of defence."
Maury was also very fully occupied in the preparation of a series of geographical class-books for the use of schools. While he was in Paris he had received a letter from Mr.
