bird, but
not more in proportion to your size. You are absolutely stronger, but
not relatively."

"What do you mean by that?" said Nathan.

"Why, you have actually more strength than a bird,--a robin, for
instance; you could hold him so that he could not get away; and you
could lift more than he could too. But then you are a great deal
larger, and you are not as much stronger than he is, as you are larger.
If you are a hundred times as heavy as he, you are not a hundred times
as strong. That's what I mean by saying that you are absolutely
stronger, but not relatively. That is, you are not as many times
stronger, as you are larger and heavier. You are absolutely stronger,
but not relatively; that is, in proportion to your size and weight.

"Now I can prove to you," continued his father, "that you would not be
strong enough to fly with wings, even if you had them. Suppose there was
a pole fastened across the room, and another pole just above it; could
you pull yourself up, from one pole to the other, by your hands alone,
without touching your feet?--Or a ladder," continued his father,--"it
will be better to suppose a ladder. Now, if there was a ladder leaning
up against a building, could you climb up on the under side by your
hands, drawing yourself up, hand over hand, without touching your feet?"

Here Rollo, who was reading in a little chair at the back part of the
room, when his father first commenced the conversation with Nathan, but
who had been listening for a few minutes past to what his father had
been saying, jumped up, and came across the room to his father, and
said,--

"Yes, sir, yes, sir; I can. I have done it often in the barn."

"How high up could you go?" said his father.

"O, almost up to the loft," said Rollo. "Only, you see, father, the
rounds are too far up. I can't reach up very well. If they were nearer
together, I could climb up so, very well."

"Well," said his father, "a bird, when flying, has to climb up in much
the same way. He has to pull himself up by the _air_, with his wings,
just as you do with your hands and arms, by the rounds of the ladder;
only the air is not fixed, like the ladder, but constantly gives way
under his wing; and so, to make the case the same, you must suppose that
the ladder is not firm, but is floating in the air, and sinks down with
your weight, so that you have to climb up faster than you pull the
ladder down. Do you think you would have strength enough in yo