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Updated: July 28, 2025
Yet in North America there are woodpeckers which feed largely on fruit, and others with elongated wings which chase insects on the wing; and on the plains of La Plata, where not a tree grows, there is a woodpecker, which in every essential part of its organisation, even in its colouring, in the harsh tone of its voice, and undulatory flight, told me plainly of its close blood-relationship to our common species; yet it is a woodpecker which never climbs a tree!
We may therefore say that our entire solar system together with every sort of material substance which it contains is made up of nothing but this one primary substance in various degrees of condensation. Now the next step is to realize that this ether is everywhere. This is shown by the undulatory theory of light.
This province lies on the northern side of the Plata, and eastward of the Uruguay: it has a gentle undulatory surface, with a basis of primary rocks; and is in most parts covered up with an unstratified mass, of no great thickness, of reddish Pampean mud.
Indiana smiled in her quiet way; she was busy filling the canoe with green boughs, which she arranged so as completely to transform the little vessel into the semblance of a floating island of evergreen; within this bower she motioned Hector to crouch down, leaving a small space for the free use of his bow, while concealed at the prow she gently and noiselessly paddled the canoe from the shore among the rice-beds, letting it remain stationary or merely rocking to and fro with the undulatory motion of the waters.
But in all early sculptural examples, both imitation and decorative effect are subordinate to easily understood symbolical language; the undulatory lines are often valuable as an enrichment of surface, but are rarely of any studied gracefulness.
She trilled along, and trilled along, and presently a handsome young page, clothed like the rainbow, and as easy and undulatory of movement as a wave, came with something on a golden salver, and, kneeling to present it to her, overdid his graces and lost his balance, and so fell lightly against her knee.
He proved the undulatory theory of light by direct experiment, but as it depended upon the hypothesis of an ethereal medium, it was not received in England, the more so as it was contrary to Newton's theory. The French savants afterwards did Young ample justice.
It has recently been objected that this is an unsafe method of arguing; but it is a method used in judging the common events of life, and has often been used by the greatest natural philosophers. The undulatory theory of light has thus been arrived at; and the belief in the revolution of the earth on its own axis was until lately supported by hardly any direct evidence.
They all refer to the repeated alterations, often in undulatory planes, of glassy, pearly, stony, and crystalline layers: the crystalline layers, however, seem to be much more perfectly developed at Ascension, than in the above-named countries. Humboldt compares some of the stony beds, when viewed from a distance, to strata of a schistose sandstone.
On this ground, though I can not accept as positive truths any of those scientific hypotheses which are unsusceptible of being ultimately brought to the test of actual induction, such, for instance, as the two theories of light, the emission theory of the last century, and the undulatory theory which predominates in the present, I am yet unable to agree with those who consider such hypotheses to be worthy of entire disregard.
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