The Recent Development of Physical Science. By W. C. D.
Whetham. (John Murray. Is. 6d. net.)—" In the following pages,' says Mr. Whetham in his introductory chapter, "an attempt will be made first to consider the philosophic foundations of physics, and then to trace some of the more important developments of the experimental investigations for which the last few years have been remarkable." And he writes a little further on that "physics is already annexing the domain of astronomy, and it has already invaded the realms of chemistry and biology." And yet not many years ago it was objected to an eminent chemist that he gave himself too much to the physical side of his science. The special bearing of physics on astronomy is exemplified in what is, perhaps, at least to the average reader, the most interest- ing chapter in the book,—" Astro-Physics." From physics we learn, among other things, to measure the heat of the sun. This is put at 6,000 C., a figure that baffles the imagination. We reach, however, the region of the imaginable when we come to the temperatures of the planets. To take our nearest neighbours only, translating the C. into the more familiar Fahrenheit, WO have Venus with a temperature of 124 deg. and Mars with 16 deg. below zero. Here, again, is an interesting speculation which takes us to a remoter region. " In their youth, suns seem to be surrounded with atmospheres principally consisting of helium and hydrogen. In their magnificent and turbulent prime, they are swathed in glowing robes of metallic vapour, still covered with the gauzy veil of helium and hydrogen. As they decline in vigour their light grows redder, like that of a cooling iron bar. Of their ultimate condition, the same analogy, and the inferred existence of dark companions, give us some suggestion. Evidence, too, indicating the occasional possibility of a stellar resurrection is not withheld from us." The other chapters will be found not less instructive.
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