ON THE MOTIONS OF SOUND. 417 



alone has the book met a i)ublic want, but also in tl)at learned land to 

 which I owe my scientific education. 



Before me, on the other hand, lie two volumes, of foolscaji size, 

 curiously stitched, and printed in characters the meanino- of which I 

 am incompetent to penetrate. Here and there, however, I notice the 

 familiar figures of the former editions of " Sound." For these vol- 

 umes I am indebted to Mr. John Fryer, of Shanghai, who, along with 

 them, favored me, a few weeks ago, with a letter, from which the fol- 

 lowing is an extract : " One day," writes Mr. Fryer, " soon after the 

 first copy of your work on ' Sound' reached Shanghai, I was readino- 

 it in my study, Avhen an intelligent official, named Hsii-chung-hu, no- 

 ticed some of the engravings, and asked me to explain them to him. 

 He became so deeply interested in the subject of Acoustics, that 

 nothing would satisfy him but to make a translation. Since, how- 

 ever, engineering and other works were then considered to be of 

 more practical importance by the higher authorities, we agreed to 

 translate your work during our leisure time every evening, and pub- 

 lish it separately ourselves. Our translation, however, when com- 

 pleted, and shown to the higher officials, so much interested them 

 and pleased them, that they at once ordered it to be published at the 

 expense of the Government, and sold at cost price. The price is four 

 hundred and eighty copper cash per copy, or about one shilling and 

 eightpence. This will give you an idea of the cheapness of native 

 printing." Mr. Fryer adds that his Chinese friend had no difficulty 

 in grasping every idea in the book. 



The new matter of greatest importance which has been introduced 

 into this edition is an account of an iuvestis^ation which, during the 

 two past years, I have had the honor of conducting in connection 

 w^ith the Elder Brethren of the Trinity House. Under the title " Re- 

 searches on the Acoustic Transparency of the Atmosphere, in relation 

 to the Question of Fog-signaling," the subject is treated in Chapter 

 VH. of this volume. It was only by governmental appliances that 

 such an investigation could have been made ; and it gives me pleasure 

 to believe that not only have the practical objects of the inquiry been 

 secured, but that a crowd of scientific errors, which for more than a 

 century and a half have surrounded this subject, have been removed, 

 their place being now taken by the sure and certain truth of Nature. 

 In drawing up the account of this laborious inquiry, I aimed at linking 

 the observations so together, that they alone should offer a substantial 

 demonstration of the principles involved. Further labors enabled me 

 to bring the whole inquiry within the firm grasp of experiment., and 

 thus to give it a certainty which, without this final guarantee, it could 

 scarcely have enjoyed. 



Immediately after the publication of the first brief abstract of the 

 investigation, it was subjected to criticism. To this I did not deem 



TOL. TII. 27 



