Page:Popular Science Monthly Volume 46.djvu/127

, "he studied medicine, and went through the whole course requisite for the attainment of a degree. He devoted his leisure for a period to the study of natural history, and was no mean proficient in geology and mineralogy, as well as in physics and chemistry. He was an active member of the Pennsylvania Geological Society, of the Committee of the Franklin Institute on Science and Art, and one of the most useful members of the American Philosophical Society. By frequent articles upon scientific topics in the various prints, by elaborate reports upon various subjects to the Franklin Institute, and by monthly announcements in its Journal of occultations and other celestial phenomena, he kept awake the interest and sympathy of the community for studies of this character. Among other labors, he prepared, in 1834, an ingenious set of parallactic tables, by which the time required for computing the phases of an occultation was reduced to less than half an hour. These were calculated for the latitude of Philadelphia, and it was his intention to publish them in a more general form adapted to different latitudes. But, as this would have been a work requiring considerable time, he subsequently abandoned the project, believing that he could employ his leisure hours more usefully. He continued the computation of the occultations without interruption for six years, and then induced our well-known colleague, Mr. Downes, to undertake the continuance of the work. It has been prosecuted to the present time, with what success we all know, and has of late years been published by the Smithsonian Institution and the Astronomical Ephemeris. Astronomy and geography in America are much indebted to Mr. Walker for these labors, since many already in possession of the necessary means were stimulated by the periodical announcements, and by his personal exertions in still other ways, direct and indirect, to observe these phenomena. An extensive series of such observations was collected by Mr. Walker and published in the Proceedings of the American Philosophical Society."

During most of Walker's residence in Philadelphia he must be regarded as an amateur rather than a scientist. For many years his interest in Nature was spread over several fields, but gradually it concentrated upon astronomy. He had procured an astronomical clock, a twenty-inch transit instrument, and a small Dollond telescope, and from about the time when he gave up his school to become actuary of the insurance company all his leisure was devoted to astronomical observation and study. "In 1837,"