Length. Distance between foci. Width. Inches. Inches. Inches.
2 1 13/4 2 11/2 11/4
21/2 1 21/4 21/2 11/2 2 21/2 2 11/2
3 1 11/2 3 11/2 2-7/8 3 2 2-5/8 3 21/2 21/4
31/2 1 3-3/8 31/2 11/2 3-1/8 31/2 2 2-7/8 31/2 21/2 21/2 31/2 3 13/4
4 2 31/2 4 21/2 3-1/8 4 3 2-5/8 4 31/2 2
5 3 4 5 4 3
For larger ovals multiples of these numbers may be taken; thus for 7 and 4, take from the table twice the width corresponding to 31/2 and 2, which is twice 2-7/8, or 53/4. It will be noticed also that columns 2 and 3 are interchangeable.
To use the apparatus in connection with the table: Find the length of the desired oval in the first column of the table, and the width most nearly corresponding to that desired in the third column. The corresponding number in the middle column tells which hole the needle must be passed through. The tack D, around which the string must pass, is so placed that the total length of the string AD + DC, or its equal AE + EC, shall equal the greater diameter of the ellipse. In the figure it is placed 61/2 inches from A, and 11/2 inches from C, making the total length of string 8 inches. The oval described will then be 8 inches long and 61/4 inches wide.
The above table will be found equally useful in describing ovals by fastening the ends of the string to the drawing as is recommended in all the text books on the subject. On the other hand, the instrument may be set “by guess” when no particular accuracy is required.
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THE MANUFACTURE OF CHARCOAL IN KILNS.
The manufacture of charcoal in kilns was declared many years ago, after a series of experiments made in poorly constructed furnaces, to be unprofitable, and the subject is dismissed by most writers with the remark, that in order to use the method economically the products of distillation, both liquid and gaseous, must be collected. T. Egleston, Ph.D., of the School of Mines, New York, has read a paper on the subject before the American Institute of Mining Engineers, from which we extract as follows: As there are many SILVER DISTRICTS IN THE WEST where coke cannot be had at such a price as will allow of its being used, and where the ores are of such a nature that wood cannot be used in a reverberatory furnace, the most economical method of making charcoal is an important question.