SKETCH OF SEARS COOK WALKER. 117 



dress,* " he studied medicine, and went tlirougli 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 pro- 

 ficient in geology and mineralogy, as well as in physics and chem- 

 istry. 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 Philadel- 

 phia, 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 with- 

 out 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 Smithso- 

 nian 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 obser- 

 vations was collected by Mr. Walker and published in the Pro- 

 ceedings 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 gradu- 

 ally it concentrated upon astronomy. He had procured an astro- 

 nomical clock, a twenty-inch transit instrument, and a small Dol- 

 lond 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. " la 1837,' 



* An Address in Commemoration of Sears Cook Walker, delivered before the American 

 Association for the Advancement of Science, at its meeting in Washington, April 29, 1854. 

 From this address many facts concerning Walker's life and work in addition to the above 

 quotation have been drawn. 



