ac^emv 0F sciences] POWELL'S SURVEY 115 



ington in May, 1877, 2 at which time he supposed it to be novel. He has since learned that he 

 was antedated in publication by no less than two hypsometers, while it is probable that a third 

 also anticipated him in the conception of the idea. Nevertheless the announcement of his 

 method was not devoid of novelty, for he differed radically from his predecessors in his manner 

 of developing and applying the idea" (548). Second, the expense attendant upon the mainte- 

 nance of two base stations and the rapid extension of lines of level and chains of triangles shortly 

 after Gilbert's essay was published worked against the adoption of his method. The labor that 

 he put into it has been hardly repaid by the few measurements of altitude in which it has been 

 employed. Twenty years later he wrote of this work: 



The discussion . . . has been complimented, but the "new method" never got itself used. 

 DIURNAL VARIATION OF THE BAROMETER 



Reference may be made at once to a return to one phase of these barometric studies in 

 Gilbert's second address as president of the Society of American Naturalists in 1886, when he 

 gave a closely argued discussion on "Special processes of research," with particular reference to 

 graphic devices. Among various other problems, that of the diurnal variation of the barometer 

 was taken up, and Espy, the early American meteorologist who gained after death the renown 

 that he should have had while living, is credited with the idea which, judging by the notes 

 quoted above, Gilbert himself appears to have reached independently while he was in the high 

 plateaus of Utah in 1875; namely, that the double diurnal curve of total atmospheric pressure 

 is a reaction from the single diurnal curve of lower atmospheric temperature. The idea is then 

 tested with negative results, for while it appears satisfactory for certain regions, it fails in other 

 regions. Thus Gilbert was led to revise the hypothesis and to conclude that "the relation of 

 the temperature oscillation to the pressure oscillation is less simple than the one suggested by 

 Espy." 3 In case other investigators take up this elusive problem, it should be noted that 

 Gilbert's assumption of a constant rate of terrestrial radiation to outer space may probably be 

 modified to advantage; for such radiation should vary between the wide limits of equality to 

 indirect and weak insolation at the time of the early morning temperature minimum and equality 

 to direct and strong insolation at the time of the early afternoon temperature maximum. It 

 may be added that Gilbert's "special processes of research" differed about as greatly from the 

 research processes usually employed by the body of naturalists whom he addressed, as his 

 hypsometric method differed from the methods of geological research usually employed by the 

 many readers who resorted for information and inspiration to the remarkable series of essays, 

 published along with his barometric essay, in the annual reports of the national survey; but if 

 the geologists and naturalists who naturally have their own methods of investigation wish 

 really to know the Gilbert whom they all delighted to honor, they must study his methods of 

 investigation in all their variety and in all their breadth and depth. 



GEOLOGY OF THE BLACK HILLS 



A report on the " Geology and resources of the Black Hills of Dakota," published by the 

 Powell survey in 1880 under the apparent authorship of Henry Newton and W. P. Jenney, 

 and including several supplements by experts on various subjects, deserves mention here because 

 it exhibits two of Gilbert's well-marked, one might say most strongly marked, characteristics — 

 generosity and acumen — for although a bibliographer, guided by the title-page only, would 

 not give him credit as even part author of the volume, a biographer guided by the preface and 

 the text must not fail to recognize his large share in the preparation of its first 220 pages, or 

 nearly half of the whole. The story of the report is one of tragic interest. During the decades 

 following the middle of the nineteenth century the Black Hills served for some 50,000 Sioux 

 Indians as a cherished resort; indeed, some of them thought of it as a "final refuge" after their 

 removal from farther east; but as gold was discovered in the hills in 1874 a fuller knowledge 

 of their geology and resources was called for than several hasty reconnaissances of earlier years 



1 Bull. Phi], Soc. Washington, ii, 1877, 131-132. 

 8 Amer. Journ. Sci., xixiii, 1887, 452-473; see 472. 



