270 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
or to be exploded electrically from a distance. A torpedo differs 
from a submarine mine chiefly in that it is provided with a vehicle 
for its transportation to a distance. 
The first recorded experiments with submarine mines were made 
by David Bushnell, of Connecticut, in 1775. His mines contained 
charges of black powder and explosion was effected by means of 
clockwork which, after being set in motion, allowed sufficient time 
for the operator to get away before the explosion. Bushnell also 
constructed a submarine boat for the purpose of conveying his mines 
to hostile vessels. With such a boat an attempt was actually made 
in 1776 to sink the British man-of-war Hagle in New York harbor. 
An important step in the development of submarine mines was made 
Fic. 7.—Submarine mine. 
in 1842 by Samuel Colt in applying electricity to the firing of such 
mines. Mines and torpedoes were first successfully used during our 
Civil War. Although of rather crude construction, they succeeded 
in sinking or seriously damaging more than 30 ships. Their success 
turned the attention of the world to this method of naval attack and 
defense, with the result that there have followed great improvements 
in appliances and methods. 
The sketch (fig. 7) shows a submarine mine of the type planted 
in waterways with a view to closing the entrance to harbors. Such 
a mine is usually controlled electrically from shore, but may be set 
to operate upon being struck by a passing ship. The steel case is 
either spherical or cylindrical, depending upon the quantity of 
explosive carried. The amount usually carried is from 100 to 500 
pounds, although there is no special reason why even greater quan- 
tities may not be carried. 
