riiiLOBorinoAii society of wasiiinqton. IMT) 



liifj; only 18 kcooikIs. Oh a li»,rf.'0 hlofk of soft Iiidia-riihlicr rcHt- 

 iiifi^ on tlio uiiuldt) hIuI), tlu! vihruliuii wan very nipidly cxUn- 

 {jjuisluid, hut without givinj^ any 8cii8iI)I« Konnd. 'I'liin luionuily 

 rcMjiiirr.d nn f.xpliiruUion. Uy niciuiH <ii' a c()ni|H)iin<l wiio of (-(iiiiicr 

 and iron inHcrttid into tlu! pioc-t; ul' iiiltbcr, and liavin}^- tlio lixtrcnii- 

 ties conncctcti witii a tiu!rnio-galvaiioincl(!r it was I'onnd tliat in 

 this caso tho acoustic vil)ratioii8 wcro convurtcd into heat. Hhoctw 

 of India-riiblxT thcircforo are ainonj; the Ix'st ahsorltcrs and de- 

 stroyers of sound. A series ol' experiments was also made on tlio 

 rtilieetioii of sound, to deterniiuo tho materials least and those best 

 atlapted to this purpose. A resume of these researches, haviti}^- 

 reference to tlie acoustic properties of put)lic iuills, was read beforo 

 the American Association in August, 1800. 



In 18(i5, as Chairman of the Connnitteo of Experiments of the 

 U. H. Iiight-hous(! Hoard, ileury eommeiu-ed an extended series 

 of observations on tlie ctondiiet and intensity of sound at a distance, 

 \inder varying ni<;t(!orologicid conditions. Weil awan; (hat for llio 

 practical purposes of giving increased security t(j navigation, llui 

 experiments of tho laboratory were of little value, he nnderlooli a 

 number of experimental trips on board sailing vessels, ami on 

 steamers, in order to make his observations under the actual con- 

 ditions of the recpiired service!. As many of his investigations 

 re(|uircd intellig(!nt co-operation, and som(;limes at the distances 

 of many miles, he associated with him at dilVerent times, among 

 m(!mbers of the Light-house hibitablitiliment. Commodore I'owell, 

 Commodore Case, Ailnural Trenchard, Commander Walker, Cap- 

 tain Upshur, (Jeneral I'oe, (leneral liarnard, (ieneral Woodrulf, 

 Mr. Ledei'le, and other engiru-ers of dilferent liighl-hoiise Dis- 

 tricts, and outside of the establishment. Dr. Welling and others. 



At thoouthct of his experiments, he found that sound rellectors, 

 which play so interesting a part in lecture room exhibitions, were 

 practically worthless (of whatever availalde dim<;uhions) for the 

 |)urpose of directing or concentrating powerful sounds to any con- 

 siderable distatice. At the distance of a mile or two a large 

 steam whistle phured in the focus of a concave reflector 10 feet in 

 diameter co.dd be heard very nearly as well directly behind tho 

 reflector, as directly In front of it. in like manner the direction 

 of bell-mouths and of trum|)et-mouths, was found to la; of com- 

 paratively littli! im|>ortauce at a <listanco ; showing the rcinnirlvablo 

 tendency to dilfusion, especially with very loud sounds. Most of 

 the observations made on shi|)- board were afterward repeateil on 

 land ; and several weeks were occupied with these important re- 

 searches. 



" During this series of investigations an interesting fact was dis- 

 coveriMl, na,mely, a soun<l moving against the wind, inaudible to 

 the ear on the deck of the si'hooticir, was heard by ascending to the 

 niastdicad. This remarkable fact at flrst suggested the idea that 



110 



