420 THE POPULAR SCIENCE MONTHLY. 



maximum sound; while the best result with the unaided siren was 

 obtained when tlie impulses were 360 a second. Experiments were 

 also made on the influence of pressure ; from which it appeared that, 

 when the pressure varied from 100 lbs. to 20 lbs., the distance reached 

 by the sound (as determined by the vibrating membrane) varied only 

 in the ratio of 61 to 51. Prof. Henry also showed the sound of the 

 fog-trumpet to be independent of the material employed in its con- 

 struction ; and he furthermore observed the decay of the sound when 

 the anffular distance from the axis of the instrument was increased. 

 Further observations were made by Prof. Henry and his colleagues in 

 August, 1873, and in August and September, 1874. In the brief but 

 interesting account of these experiments an hypothetical element ap- 

 pears, which is absent from the record of the earlier observations. 



It is quite evident from the foregoing that, in regard to the ques- 

 tion of fofy-sienalins:, the Lighthouse Board of Washington have not 

 been idle. Add to this the fact that their eminent chairman gives his 

 services gratuitously, conducting without fee or reward experiments 

 and observations of the character here revealed, and I think it will be 

 conceded that he not only deserves well of his own country, but also 

 sets his younger scientific contemporaries, both in his country and 

 ours, an example of high-minded devotion. 



I was quite aware, in a general way, that labors like those now for 

 the first time made public bad been conducted in the United States, 

 and this knowledge was not without influence upon my conduct. The 

 first instruments mounted at the South Foreland were of English manu- 

 facture; and I, on various accounts, entertained a strong sympathy 

 for their able constructor, Mr. Holmes. From the outset, however, I 

 resolved to suppress such feelings, as well as all other extraneous con- 

 siderations, individual or national, and to aim at obtaining the best 

 instruments, irrespective of the country which produced them. In 

 reporting, accordingly, on the observations of May 19 and 20, 1873 

 (our first two days at the South Foreland), these were my words to 

 the Elder Brethren of the Trinity House : 



"In view of tlie reported performance of horus and whistles in other places, 

 the question arises whether those mounted at the South Foreland, and to wbicli 

 the foregoing remarks refer, are of the best possible description. ... I think 

 our first duty is to make ourselves acquainted with the best instruments hitherto 

 made, no matter where made; and then, if home genius can transcend them, to 

 give it all encouragement. Great and unnecessary expense may be incurred, 

 through our not availing ourselves of the results of existing experience. 



"I have always sympathized, and I shall always sympathize, with the desire 

 of the Elder Brethren to encourage the inventor who first made the magneto- 

 electric light available for lighthouse purposes. I regard his aid and counsel as, 

 in many respects, invaluable to the corporation. But however original he may 

 be, our duty is to demand that his genius shall be expended in making advances 

 on that which has been already achieved elsewhere. If the whistles and horns 

 that we heard on the 19th and 20th be the very best hitherto constructed, my 



