Place two concave mirrors at about twelve feet distance from each other, and let the axis of each be in the same line. In the focus of one of them place a live coal, and in the focus of the other some gunpowder. With a pair of strong bellows keep blowing the coal, and notwithstanding the distance between them, the powder will presently take fire.
The mirror may be either made of glass, metal, or pasteboard gilt.
To find the Number of Changes that may be rung on Twelve Bells.
Multiply the numbers from 1 to 12 continually into each other, as follow: and the last product will give the number required.
1
2
——
2
3
——
6
4
——
24
5
———
120
6
———
720
7
————
5,040
8
—————
40,320
9
——————
362,880
10
———————
3,628,800
11
——————————
39,916,800
12
——————————
479,001,600
To find how many square Yards it would require to write all the Changes of the Twenty-four Letters of the Alphabet, written so small, that each Letter should not occupy more than the hundredth part of a square Inch.
By adopting the plan of the preceding article, the changes of the twenty-four letters will be found to be
62,044,840,173,323,943,936,000.
Now, the inches in a square yard being 1,296, that number multiplied by 100 gives 129,600, which is the number of letters each square yard will contain; therefore, if we divide the above row of figures, (the number of changes,) by 129,600, the quotient, which is 478,741,050,720,092,160, will be the number of yards required to contain the above mentioned number of changes. But as all the 24 letters are contained in every permutation, it will require a space 24 times as large, viz.,