APPENDIX. 



NOTICES OF BOOKS. 



Practical Acoustics. By C. L. Barnes. London : Macmillan & Co. 



1897. 



This volume forms the first instalment of the long-promised third 

 volume of Stewart and Gee's Lessons in Elementary Practical Physics. 

 To those who have been in the habit of using the previous volumes the 

 present addition will probably prove very disappointing, for the character 

 of the book is entirely different. This is no doubt partly due, as the 

 author explains in his preface, to the difficulty in the subject of acoustics 

 of devising quantitative experiments which can be carried out in a 

 laboratory having the ordinary equipment. One of the chief defects of 

 the book is that it is swamped with the description of experiments 

 which, although they are in many cases curious and interesting, are 

 perfectly unsuited for an educational work. In some cases experiments 

 are described which have not been explained, and which do not 

 illustrate any special portion of the subject. These experiments might 

 have been collected together in an appendix without much harm, but 

 scattered as they are throughout the book, they seem to give the idea 

 that the performance of pretty experiments is the aim and object of the 

 work. 



In many places the working or definitions are very obscure. Thus 

 to define the amplitude of a vibratory motion as "The displacement of 

 an antinode from its initial position " seems to restrict the definition to a 

 certain portion of a stationary wave, while the next sentence says, " the 

 mean velocity of each particle is proportional to its own amplitude". 

 The statement on page 27 that the frequency of the transverse 

 vibrations of a string varies directly as the square root of the tension, is 

 followed by the following paragraph : " It also varies directly as the 

 square root of the force of gravity, but this is commonly left out of 

 account ". These two statements are perhaps as thoroughly vicious and 

 calculated to confuse the student as any that could be compiled. Again, 

 Young's modulus is defined as the ratio of a small increment of pressure 

 to the resultant diminution of length. In using the word tension when 

 he means stretching force, the author follows a somewhat general 

 practice but one none the less to be regretted. 



The book as a whole suffers from undue expansion on the one 

 hand and from looseness of expression on the other, so that although it 

 will probably be found useful for teachers and others in quest of lecture 

 experiments, it is hardly a safe book for the use of the, at any rate the 

 elementary, student of physics. 



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