[70] see-saws,
weights and measures of various kinds, etc., etc. These are important
for both boys and girls; but, as they are uncommon, it may be well to
suggest the proper mode of using them, and the advantages they confer.

[70] Dumb-bells are usually made of cast iron, and sometimes of
bell-metal, of the shape indicated by the figure, and should weigh from
two to ten pounds each, according to the strength of the person using
them. [Illustration]

_Dumb-bells_ may be used, in connection with the sports enumerated in
the third chapter, for developing and strengthening the chest and
improving the health. I would refer any who question the fitness of such
exercises to what has been said on the subject at the 77th and following
pages, and especially to the testimony of Dr. Caldwell there introduced.

_See-saws_, in addition to the benefits that result from the exercise,
are attractive, and may be rendered highly instructive. For this
purpose, the plank or board used should be well hung and properly
balanced. The distance from the fulcrum or point of support should be
accurately graduated, and marked in feet and inches. Then, knowing the
weight of one scholar, the weights of all the others may be ascertained
by their relative distances from the fulcrum when they exactly balance.
These interesting experiments may be tried by any child as soon as he
understands the ground rules of arithmetic, and the simple fact that,
for two children to balance, the product of the weight of one multiplied
into his distance from the fulcrum will exactly equal the product of the
weight of the other into his distance from the fulcrum. Such simple
experiments, when thus mingled with sports, and made interesting to
young children, serve the double purpose of attaching them to the
school, and of fixing in their minds the habit of observation and
experiment, and of understanding the why and wherefore, which will be of
incalculable service to them all the way through life.

_Weights and measures_ serve the same general purpose, and may be
rendered well-nigh as useful as slates and black-boards. Thousands of
children recite every year the table, "four gills make a pint, two pints
make a quart, four quarts make a gallon," etc., month in and month out,
without any distinct idea of what constitutes a gill or a quart, or even
knowing which of the two is the greater. But let these measures be once
introduced into the experimental play-roo