Popular Lectures and Addresses. By Lord Kelvin (Sir William Thomson).
Vol. II. (Macmillan and Co.)—This second volume, appearing, as our readers will remember, after the third, com- pletes the collection of Sir William Thomson's lectures and addresses. The general subject is described as "Geology and General Physics." The range of topics treated is large. In the first we are told of the utility of dew. Dew in summer protects vegetation from frost, which would otherwise follow the radiation that takes place in a clear atmosphere. Another subject is " Geological Time." Believers in the old "six thousand years" chronology will not be much consoled by the conclusion that "all geological history showing continuity of life must be limited within some such period of past time as one hundred million years." On another great subject we find, limiting ourselves to conclusions, that "the earth is not a mere thin shell filled with fluid, but is, on the whole, or in great part, solid. Again, apropos of the "Dissipation of Energy," we read : "Within a finite period of time past the earth must have been, and within a finite period of time to come must again be, unfit for the habitation of man as at present constituted." By what reasoning the writer arrives at these and other conclusions, it will be well worth while to see. No one has a greater command of premises, and more skill in marshalling cogent arguments.
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