the figure. The length of the diameters may be varied at pleasure by the monitor.
There are various geometrical rules for drawing el- lipses, but it is not within the scope of our work to no- tice more than one of the simplest forms of ovals. Draw a circle and mark its centre and diameter. Then on one end of the diameter, draw another circle of the same size intersecting the former. Then opening the divi- ders the length of the diameter, place one foot on the lower point of intersection, and connect the two circles at top, and then do the same by the other point of inter- section and the bottom part of the oval.
A simple and amusing method is, to stick two pins into a piece of paper firmly, at any distance from each other ; tie the ends of a piece of string together, and put the string round both pins. Hold a pencil then at any part of the string, and move it round ; an ellipse will be formed, of which the two pins will be the two foci or centres. By lengthening or shortening the string, the figure may be made more or less elliptical.
15, Draw an oblique cone. (fig. 9.)
