The pupil goes
on from step to step simply because he has but one short step to take at
a time.
"Can it be noon, then," continues the teacher, "here and at a place
fifteen degrees west of us at the same time?"
"Can it be noon here and at a place ten miles west of us at the same
time?"
It is unnecessary to continue the illustration, for it will be very
evident to every reader that, by going forward in this way, the whole
subject may be laid out before the pupils so that they shall perfectly
understand it. They can, by a series of questions like the above, be led
to see, by their own reasoning, that time, as denoted by the clock, must
differ in every two places not upon the same meridian, and that the
difference must be exactly proportional to the difference of longitude.
So that a watch which is right in one place can not, strictly speaking,
be right in any other place east or west of the first; and that, if the
time of day at two places can be compared, either by taking a
chronometer from one to another, or by observing some celestial
phenomenon, like the eclipses of Jupiter's satellites, and ascertaining
precisely the time of their occurrence, according to the reckoning at
both, the distance east or west by degrees may be determined. The reader
will observe, too, that the method by which this explanation is made is
strictly in accordance with the principle I am illustrating, which is by
simply _dividing the process into short steps.
Pages:
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136