alone has the book met a public want, but also in that learned land to which I owe my scientific education.
Before me, on the other hand, lie two volumes, of foolscap size, curiously stitched, and printed in characters the meaning of which I am incompetent to penetrate. Here and there, however, I notice the familiar figures of the former editions of "Sound." For these volumes 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 following is an extract: "One day," writes Mr. Fryer, "soon after the first copy of your work on 'Sound' reached Shanghai, I was reading it in my study, when an intelligent official, named Hsii-chung-hu, noticed 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, however, 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 publish it separately ourselves. Our translation, however, when completed, 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 eight-pence. 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 investigation which, during the two past years, I have had the honor of conducting in connection with the Elder Brethren of the Trinity House. Under the title "Researches on the Acoustic Transparency of the Atmosphere, in relation to the Question of Fog-signaling," the subject is treated in Chapter VII. 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
