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in the Organic World . 
tain boundaries to the size of organisms which they are 
unable to exceed, yet these boundaries vary with the density 
of the medium in which such organisms are immersed. 
A denser atmosphere, just like a reduced gravitative force, 
would tend to obliterate the sharp boundary line now exist- 
ing between terrestrial and aerial animals, and would doubt- 
less re-people the world with winged saurians, gigantic 
birds, and with flying mammals. 
The effects of a highly rarefied atmosphere may easily be 
realised from what is witnessed upon lofty mountains. 
Great limitation among aerial species, and an equally great 
debilitation in terrestrial forms, could not fail to result. 
There has been no little speculation as to how the world 
must appear to beings whose whole life-time might be 
counted by minutes rather than by years. But no one 
seems to have entertained the idea that our perceptions of 
external nature and our modes of interpreting phenomena 
are to a very great extent the result of our size, and would 
change if it were modified. Such a contemplation may 
teach us some useful lessons. 
Let us in the first place suppose ourselves reduced to 
the size of the minutest living being, though preserving the 
same mental faculties, and, in proportion to our bulk, the 
same physical powers which we now enjoy. In what light 
would the most ordinary phenomena of outward nature pre- 
sent themselves? We should find an alteration, not merely 
in magnitude, but in kind. As an example, I set out for a 
journey of exploration upon a cabbage leaf, which appears 
as a plain of many square miles in extent. I find it studded 
with huge, glittering, transparent globes, each in height 
vastly exceeding my own stature, and resting motionless 
upon the surface of the leaf. Each of these appears to pour 
out, from one of its sides, a dazzling light, accompanied by 
a strong heat. Urged by curiosity, I approach and touch 
one of these orbs, when suddenly I feel myself seized upon 
and whirled round and round till I come somewhere to an 
equilibrium and remain suspended on its surface, utterly 
unable to extricate myself. In the course of an hour or two 
I find the globe diminishing, and ultimately it disappears, 
leaving me at liberty to pursue my travels. Leaving the 
cabbage leaf, I stray along over the surface of the soil, 
which has an exceedingly rocky and rugged character, until 
I see before me a broad surface of the same kind of matter 
which formed the globes on the cabbage leaf. Instead, 
however, of rising upwards from its support, I see it now 
sloping downwards in a vast curve from the brink, and 
