3. They should be closely connected with the points which they
illustrate.
4. When very short, or when so difficult as to demand the whole
attention of the teacher, they may be given and afterward discussed. If
long or easy, they may be discussed while the work is going on. Changes
which take place slowly, as those which are brought about by the gradual
action of heat, for instance, are best taken up in this latter way.
5. Exceptions may be necessary, as when experiments which demand special
preparation immediately before they are presented are given when the
recitation begins, or cases in which experiments are kept until near the
close of a recitation, when the teacher finds that attention flags and
the lesson seems to have lost its interest to the pupils as soon as the
experiments have been given.
When performed by the pupils themselves, experiments should come before
the recitation as a part of the preparation for the work of the class
room.
Even in those cases in which the teacher performs the work, opportunity
should be given, from time to time, for the performing of the experiment
by the pupils themselves. This can be done in several ways. During the
course in physics here I am in the habit of leaving apparatus on the
table in my room for at least one day, often for a longer time, and of
giving permission to my class to perform the experiments for themselves
when their time permits and the nature of the experiment makes it an
advantage to get a nearer view than was possible in the class work. I
leave it to them to decide when to perform the experiments, or whether
it is to their advantage to take the time to perform them at all. I make
no attempt to watch either pupils or apparatus, although I would
often assist or explain at intermissions or during the afternoon. The
apparatus was largely used, and the effect on recitations was a good
one. For advanced pupils, and those who can be fully trusted, the plan
is a good one. The only question is the safety of the apparatus; each
teacher can decide for himself regarding the advisability of the plan
for his own school.
With smaller pupils their own safety may render it best to keep
apparatus out of their hands, except under the immediate direction of
the teacher. With all pupils that is, doubtless, the best plan where
chemicals are concerned.
Another method is to allow pupils to assist the teacher in the
preparation of experiments, to call occasionally upon members of the
class to come forward and give the experiment in the place of the
teacher, and to encourage home work relating to experiments. This latter
is often spontaneous on the part of older pupils, and can be brought
about with the smaller ones by the use of a little tact; many of the
toys of the present day have some scientific principle at bottom; let
the teacher find out what toys his young pupils have, and encourage them
to use them in a scientific way.
In whatever ways experiments be used, the class should be made to
consider the following elements as important in every case:
1. The purpose of the experiment. The same experiment may be performed
at one time for one purpose, at another time for another. The purpose
intended should be made the prominent thing, all others being
subordinated to it. Many chemical reactions, for instance, can be made
to yield either one of two or more substances for study or examination,
or use, while it may be the purpose of the experiment to close only one
of them.
2 The apparatus. All elements should be considered. The necessary should
be separated from that which may vary. In cases where the various parts
must have some definite relation to the others as regards size or
position, all that should be considered with care. In complex apparatus
the exact office of each part should be understood.
3. A clear understanding of what happens. To this I have already
referred.