134 THE MAGNESIUM LAMP. 



that in two ways. The light, while they themselves re- 

 main behind it in the shade, shows them the enemy and 

 the defenses, if there are any, which they are to attack, 

 very clearly, and at the same time dazzles the eyes of the 

 enemy, bewilders their vision, and confuses their aim. 



In order fully to understand what is to follow, the reader 

 must not lose sight of the principle on which the magne- 

 sium light is produced namely, by the intense avidity 

 with which the oxygen of the air seeks to enter into re- 

 combination with the magnesium, from which it was sep- 

 arated by the use of great force when the metal was pre- 

 pared, and the consequent heat, which raises the solid par- 

 ticles of magnesia to a dazzling incandescence as fast as 

 they are formed. Magnesium is never found in its metal- 

 lic form in nature. It is always found already in combina- 

 tion with oxygen, either in magnesia, which is the simple 

 oxyde, or in some other form or combination in which it is 

 already oxydated; and the oxygen with which it is com- 

 bined clings to it with such tenacity that it requires a very 

 great chemical force to separate it, so as to produce the 

 metal in a pure and isolated state. 



I mean by a great chemical force a force which, though 

 really very great, is exercised within such extremely small 

 limits in respect to distance as to be entirely unapprecia- 

 ble by the senses. We have an example of a force in some 

 respects analogous to this in the freezing of water, by 

 which the particles are forced apart only to an inconceiv- 

 ably minute distance from each other, but yet with so much 

 force as to lift and displace the heaviest walls if they rest 

 upon ground that the frost can reach, or to break asunder 

 the strongest vessels when the freezing water is confined 

 in them ; and so, also, with the force with which the juices 

 are drawn up in the vessels of plants and trees in the pro- 

 cess of vegetation. This force, though inappreciable to our 



