a
wooden frame, slides along a slit or opening in a board hinged to the
inner side of the board which is cleated to the window.

A plate-glass mirror, eight by fifteen inches in size, is secured to a
board hinged to a wooden rod, which can be turned from the inside, and
is raised and lowered by a cord winding on a key. The mirror is lowered
and inclined until the sunlight is reflected through the lenses, and
then a circle of intense light, from ten to fifteen feet in diameter
appears on the wall or screen. Both lenses will not cost more than two
dollars, and the apparatus will most impressively illustrate experiments
in light and sound.

An easily made electric lamp is shown by Figure 16. An Argand chimney is
fastened to a wooden base, with the cement known as "Stratena," and
partly filled with water. A cork coated with paraffine is placed inside
the chimney, and a rod of carbon twelve inches long and one-sixteenth of
an inch in thickness being inserted in the cork, the upward pressure of
the water on the cork causes the end of the carbon rod to come in slight
contact with a thick rod of carbon which is fastened obliquely to a
square piece of wood, cemented near the top of the chimney. A brass chip
fastened to the wood keeps the thin rod of carbon in position, and when
two copper wires connect the carbons with six to ten jars of a
bichromate battery, a light appears where the two carbons meet. As the
thin rod wastes away, the cork rises and keeps the end of the rod
almost in contact with the other carbon point.

An ambition to creditably make a mechanical contrivance or apparatus is
noticeably characteristic of many boys. The construction of an aquarium,
a sailboat, or a telescope, or some similar object, is of absorbing
interest to such lads; and the making of the electrical apparatus of
straws, sealing-wax, etcetera, once described by Professor Tyndall, has
merely tasked the ingenuity of thinking boys to improve upon the
apparatus.

Many educators maintain that manual training of a pleasant character,
adapted to the age of the pupils, should form an essential element in
the education of boys and girls, and should be placed on a par with the
regular studies. There is no doubt that such instruction stimulates
ambition and tends to develop taste, skill, and natural invention. At
the same time an insight into mechanical occupations, with some
practical experience in the handling of tools, may assist a boy in
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