Every effort to elucidate what is obscure, or to provide a remedy for acknowledged evils, is a just title to that friendly acknowledgment which the writer of this little book bespeaks. It is a step in the direction of progress. But it is of the highest importance in the attempt to impart clear ideas upon any subject, that they should be so distinctly expressed as to leave no doubt concerning the identity of their subject. Thus, in treating of _sound_, it seems to us that the question first presented is this: _What is sound?_ Our author says that it “_receives_ its vitality or its life through the air, and without air sound loses it and becomes extinct.” We object to this statement of the origin of sound, as both unsatisfactory and indistinct. It implies that _sound_ is something born and floating in the air, and external to the mind perceiving. We fancy that, without _an ear to hear_, sound would not become extinct, but have no existence; and that the _vitality_ of which our writer treats is not _in_ or _on_ the air, but in the mind itself. This exception to the supposed origin of the _life of sound_ may not seem to affect the discussion of acoustics as far as the practical purpose of the architect is concerned; but we insist that neither the drumsticks nor the drum, nor the air within it or without, nor even all these at work, are _sound_, more than the telegraph wire and the electric current are the _message_ sent from one operator to another. That inaccuracy which we discover in our author’s use of terms, we find also in his quotations from others. For example: “The intensity of sound depends on the density of the air in which the sound is generated, and _not on that of the air in which it is heard_. A feeble sound becomes instantly louder as soon as the air becomes more dense. So you will always find, on great elevations in the atmosphere, the sound sensibly diminished in loudness. If two cannon are equally charged, and one fired at [from] the top of a high mountain, and the other in a valley, the one fired below, in the heavy air, may be heard above, while the one fired in the higher air will not be heard below; owing to its origin, the sound generated in the denser air is louder than that generated in the rarer. Peals of thunder are unable to penetrate the air to a distance commensurate with their intensity on account of the non-homogeneous character of the atmosphere which accompanies them; from the same cause, battles have raged and have been lost within a short distance of the reserves of the defeated army, while they were waiting for the sound of artillery to call them to the scene of action.”