Volume 1

Fragments of science : a series of detached essays, addresses, and reviews / by John Tyndall.

Date:
1879
Catalogue details

Licence: Public Domain Mark

Credit: Fragments of science : a series of detached essays, addresses, and reviews / by John Tyndall. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    oppose at the same time their approach and their retreat, but which tolerate the vibration called heat. The molecular vibration once set up is instantly shared with the aether, and diffused by it throughout space. We on the earth’s surface live night and day in the midst of ethereal commotion. The medium is never still. The cloud canopy above us may be thick enough to shut out the light of the stars; but this canopy is itself a warm body, which radiates its thermal motion through the aether. The eartli also is warm, and sends its heat-pulses incessantly forth. It is the waste of its molecular motion in space that chills the earth upon a clear night; it is the return of thermal motion from the clouds which prevents the earth’s temperature, on a cloudy night, from falliag so low. To the con- ception of space being filled, we must therefore add the conception of its being in a state of incessant tremor. The sources of this vibration are the ponderable masses of the universe. Let us take a sample of these and examine it in detail. 'NWien we look to our planet, we find it to be an aggregate of solids, liquids, and gases. Subjected to a sufficiently low temperature, the two last would also assume the solid form. When we look at any one of these, we generally find it composed of still more elementary ]3arts. We learn, for example, that the water of our rivers is formed by the union, in definite proportions, of two gases, oxygen and hydrogen. We know how to bring these constituents together, so as to form water : we also know how to analyse the water, and recover from it its two constituents. So, likewise, as regards the solid portions of the earth. Our chalk hills, for example, are formed by a combination of car- bon, oxygen, and calcium. These are the so-called elements the union of which, in definite proportions, has