ON COMBUSTION BY INVISIBLE RAYS. 
19 
miles at sea; how much further remains to be determined. Commissions under several 
Governments are investigating its capabilities, and there is reason to believe that it will 
very soon be adopted for ship signals and lighthouses. It has been suggested that rockets 
primed with magnesium in powder and thrown up at uncertain intervals would effec¬ 
tually prevent a night surprise, as they would light up the country for miles around. 
By the same means many of the secrets of an enemy’s works and position might be 
discovered. Had the United States’ Navy possessed the light sooner, the hazards of 
blockade-running would have been indefinitely increased. Its merits were only revealed 
when the opportunities for its employment were passing away. We read in the ‘ Times,’ 
of 20th February of the present year:— 
“It appears that, according to.Federal anticipations, blockade-running is likely to 
suffer a check by the introduction into the American Navy of the new magnesium light, 
of which metal the Washington Government has ordered a supply. Several of the 
European Governments, it is also said, are engaged in experiments with a view to its 
adaptation to lighthouses and coast and sea signals.” 
An American Magnesium Company has been formed to work Sonstadt’s patents in 
Boston; and it will be singular if that enterprise, ingenuity, and fertility of resource, 
which have placed the name of New England in the highest rank in the arts alike of 
peace and war, do not quickly surprise us with some bold applications of the metal. 
It is hardly necessary to describe magnesium. In wire or ribbon it has become a com¬ 
mon object in shop .windows. It is white—brilliant as silver when pure and clean. In 
dry air it preserves its lustre, but in moisture it oxidizes and gets dull as zinc. Its specific 
gravity is 1 */5, or about one-fifth that of copper, which is 8'96. Aluminium is a very 
light metal, but its specific gravity is 2 - 5G—much denser than magnesium. Silver 10*50 ; 
an ounce of magnesium is therefore six times the bulk of an ounce of silver. 
We have confined ourselves to the uses of magnesium as a light-giver. That use has 
been so obvious, and pregnant with so many advantages, that it has absorbed all at¬ 
tention ; but it is scarcely probable that magnesium will continue to be made for burn¬ 
ing only. It has surely other merits ; but much, very much, remains to be learnt about 
it. What is its value as a conductor of electricity ? Under what conditions is it ductile ? 
—under what fragile ? What is the degree of its tenacity—its strength under tension ? 
What is its specific heat ? What are the characters of its alloys ? These and scores of 
other questions have yet to be answered with scientific precision. 
People are constantly drawing conclusions from the present price of magnesium. 
Reasoners were last summer deciding that this and that could never be done, because it 
was selling in wire at 3d. per foot. Now that it is selling at Id., where are their conclu¬ 
sions ? Arguments from such premises are idle. No one can tell at what price magne¬ 
sium may be produced. Many improvements in the processes of production have been 
effected since the Magnesium Company commenced working, and their experience will 
beget others; their art is young—not yet two years old. Price, moreover, is largely depen¬ 
dent on the scale of production. If iron was worked on the present scale of magnesium, 
at what price would iron wire be retailed per foot ? Whenever magnesium is demanded 
in large quantities, its price will fall. The Magnesium Company look wistfully for great 
consumers, for various economies at their command are only practicable on extensive 
plans. They could, and they desire earnestly, to produce cheaply ; they only await op¬ 
portunity. Dr. Percy informs us, that no one need think of smelting copper with less 
capital than £50,000 ; the requisite economies are impossible on smaller means. Should 
magnesium ever be used as freely as copper, who can predict what may be its price ?— 
Technologist. 
ON COMBUSTION BY INVISIBLE RAYS. 
PROFESSOR TYNDALL, F.R.S., M.R.I. 
Delivered at the Royal Institution of, Great Britain , Friday , January 20, 18G5. 
We are so accustomed to associate the word ray with the idea of light, that the term 
dark, or invisible, or obscure rays, stimulates the imagination by its strangeness; and 
such is more particularly the case when we are told that the major portion of the radia¬ 
tion of the sun itself is of this invisible character. This great discovery was announced 
