PHILOSOPHICAL SOCIETY OP WASHINGTON. 353 



trips of 10, 15 and even 20 miles in sin<rle stretches, in calm, in 

 sunshine, in storm, with every variety of disregarded exposure, 

 form altogether a labor and a research — quite unequalled and uii- 

 approached by any siuiilar ones on record. As a result of so 

 great earnestness and thoroughness in the conduct of an enter- 

 prise of so great difficulty, Henry has advanced and enriched 

 our knowledge by contributions to the science of acoustics un- 

 questionably the most important and valuable of the century. 

 By persistent cross-examination of tiie bewildering anomalies of 

 sound propagation under wide diversities of locality and con- 

 dition, he has succeeded in evolving order out of apparent chaos, 

 — in reclaiming a new district, now subjected to the orderly reign 

 of recognized law, — and iu raising the plausible but long neglected 

 hypothesis of Stokes into the domain of a verified and fully estab- 

 lished theory. Only on the subject of the ocean echo had he 

 failed to reach a solution which entirely satisfied his judgment;" 

 and at the ripe age of four score years he had mapped out a 

 further extension of his laborious search after truth, when his 

 beneficent and all unselfish purposes were cut short by death. 



With these great labors (a full demand upon the energies of 

 youthful vigor) fittingly closed the life of one whose long career 

 liad been dedicated to the servif'e of his race, — no less by the un- 

 recorded incitations and encouragements of others to the prose- 

 cution of original research, than by his own earnest efforts on all 

 convenient occasions to extend the boundaries of our knowledge. 

 Nor is it permitted us to indulge in vain regrets that thirty years 

 of such a life were seemingly so much withdrawn from his own 

 chosen ministry at the altar of science, to be occupied so largely 

 with the drudgery and the routine of merely administrative duties. 

 True though it be, that talents adapted to such functions are very 

 much more common and available than those which form the suc- 

 cessful interrogator of Nature, who that knows by what exertions 

 Smithson's wise endowment was rescued from the wasteful dissi- 

 jiation of heterogeneous local agencies nnd objects — by what 

 heroic constancy, and through what ordeals of remonstrance and 



* " The question, therefore, remains to be auswered : what is the cause 

 of the aerial echo ? As I have stated, it must in some way be connected 

 witlx the horizon. The only explanation which suggests itself to me at 

 present is, that the spread of tlie sound wliich fills the whole atmosphere 

 from the zenith to the horizon with sound-waves, may continue their 

 curvilinear direction until they strike the surface of the water at such 

 an angle and direction as to be reflected back to the ear of the observer. 

 In this case the echo would be lieard from a perfectly flat surface of 

 water, and as different sound-rays wo ild reach the water at different dis- 

 tances and from different azimuths, they would produce the prolonged 

 character of the echo and its angular extent along the horizon. While 

 we do not advanca this hypothesis as a final solution of the question, we 

 shall provisionally adopt it as a means of suggesting further experiments 

 in regard to this perplexing question at another season." (^Report of 

 Light House Board, 1&77, p. 70.) 



VOL. II.— 23 127 



