PHILOSOPHICAL SOCIETY OP WASHINGTON. 353 



trips of 10, 15 and even 20 miles in single stretches, in calm in 

 sunshine, in storm, with every variety of disregarded exposure 

 lorm altogether a labor and a research— quite unequalled and un- 

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

 great earnestness and thoroughness in the conduct of an enter- 

 prise of so great difBculty, Henry has advanced and enriclaed 

 our knowledge by contributions to the science of acoustics un- 

 questionably the most important and valuable of tlie century 

 By persistent cross-examination of the bewildering anomalies of 

 sound jjropagation 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 rei-n 

 ot recognized hiw,_and in raising the plausible but lono- ne'o-lected 

 hypothesis of Stokes into the domain of a verified and fully''e«tab- 

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

 tailed to reach a solution which entirely satisfied his judgment-- 

 and at tbe ripe age of four score years he bad mapped out'a 

 turther 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 

 had been dedicated to the service 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 efi"orts on all 

 convenient occasions to extend the boundaries of our knowledo-e 

 Nov IS It permitted us to indulge in vain regrets that thirty years 

 ot such a life were seemingly so much withdrawn from his own 

 chosen ministry at the altar of science, to be occupied so lar-elv 

 with the drudgery and the routine of merely administrative duties 

 Irue 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 

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

 pation of heterogeneous local agencies and objects— by what 

 heroic constancy, and through what ordeals of remonstrance and 



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

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

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

 present is, that the spread of the sound which fills the whole atmosphere 

 from the zemth 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 

 lu this case the echo would be heard from a perfectly flat surface of 

 water, and as different sound-rays woald reach the water at difi-erent 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 advance this hypothesis as a final solution of the question we 



?rrLCr°n ^ ^^"?^ '■ ^' ^ '""'""' '^ suggesting further Experiments 

 m rega^-d to this perplexing question at ?inother season." (/iepori of 

 Light House Board, 1877, p. 70.) K^^^lJori oj 



127 



