Popular Science Monthly 



by the ship and causes the main charge 

 to explode. 



In order to make a mine field as ef- 

 fective as possible loose ropes are some- 

 times connected between different mines 

 with the object of getting the ship's pro- 

 peller entangled in the rope and thereby 

 drawing the mine towards the ship and 

 exploding it. 



A 



Launching a submarine mine 



Mines of the type described 

 are easily laid. When stowed 

 away on the deck of a mine-lay- 

 ing ship the mine rests on the 

 anchor which at the same time 

 forms a little carriage to be run 

 along the deck and simply 

 dropped over the stern of the 

 ship at the right moment. 



Whether mines have actually 

 been laid by submarines is, of 

 course, known only to the naval 

 authorities. Patents have, how- 

 ever, been taken out within the 

 last few years for specially de- 



23 



signed mines to be laid by submarines 

 and also for providing submarine boats 

 with a series of chambers on each side 

 for holding and launching mines. These 

 chambers are disposed between double 

 walls of the submarine and are made to 

 form a smooth outline with the hull of 

 the boat. This provision makes it pos- 

 sible to carry a double cargo. 



Mines Which Become Ineffective 

 After a Certain Period 



Unanchored automatic or floating 

 mines must be dead in an hour. They 

 are used to some extent in naval battles 

 and are very cheap in construction. In 

 some mines of this type clockwork is 

 used which after an hour throws the fir- 

 ing gear out of action while in another 

 type delay-action devices for opening 

 valves to admit water are employed so 

 that the mine is sunk after a definite 

 time interval. 



To some extent chemical methods are 

 employed to fire the charge, in floating 

 mines, but a disadvantage is that the 

 explosion does not take place instantane- 

 ously as is the case with a mechanically 

 fired mine. A glass tube is attached to 

 the mine which is broken when struck 

 by a ship ; water enters and by coming 

 in contact with sodium or potassium fires 

 the charge. Other chemicals such as sul- 

 phuric acid have also been used to fire 

 the charges in floating mines. 



¥^- 



f^ 



Loading an American mine. Unanchored 

 automatic or floating mines must be dead 

 in an hour. Various devices are incorpo- 

 rated to obtain this result 



