Notices respecting New Books. 75 



The principal subjects discussed in the second lecture are the 

 physical difference between noises and musical sounds, the nature 

 of musical pitch, the connexion between the pitch and wave-length 

 of musical sounds, and the limits of pitch within which sounds are 

 audible and available for musical purposes. 



The whole of the third lecture is devoted to the explanation of the 

 laws of vibrating strings. Some beautiful experiments in illustration 

 of this subject, which were made known a few years ago by Professor 

 Melde of Marburg, have been extended by Professor Tyndall with 

 wonderful ingenuity, so that he is able in this lecture to render stri- 

 kingly visible the separate effect of each of the conditions upon 

 which the rate of vibration of a stretched string depends. For their 

 combination of intrinsic beauty with demonstrative value, the expe- 

 riments described in this lecture are perhaps on the whole the most 

 remarkable in the book; and the verbal explanations of the phenomena 

 they are intended to illustrate are not less excellent. The production 

 of stationary vibrations, by the combined action of direct and reflected 

 progressive waves, however, is a subject which, considering its im- 

 portance, might with advantage have been discussed rather more fully. 



The fourth lecture treats of the transverse vibrations of rods and 

 plates ; but, though full of excellent matter, it presents less of 

 novelty, either in the way of experiment or of exposition, than most 

 of the others. An accidental transposition on page 151 produces a 

 misstatement : the number of vibrations of a bell in a given time 

 is said to vary " directly as the square of the thickness, and in- 

 versely as the bell's diameter," instead of directly as the thickness, 

 and inversely as the square of the bell's diameter. 



The fifth lecture is taken up with the laws of the longitudinal vi- 

 brations, first of solid bodies, and then of air and gases, naturally in- 

 cluding the theory of organ-pipes and indirect methods of measuring 

 the velocity of sound. A little misconception may, we think, pos- 

 sibly arise with regard to the nature of longitudinal vibrations 

 if they are spoken of, as is the case several times in this lecture, as 

 "running to and fro." Although they take place lengthwise, they 

 are of course as stationary and unprogressive as transverse vibrations. 

 The results of Helmholtz's researches into the nature of the vowel- 

 sounds, and Kundt's method of comparing the relative velocities of 

 sound in air and in solid bodies, are very lucidly explained in this 

 lecture for the first time, so far as we know, in an English elementary 

 work. 



From the consideration of the vibrations of air in organ-pipes, it 

 is an easy transition to the examination of the similar vibrations 

 produced in the air contained in a glass tube by a burning gas-jet, 

 and thence to the investigation of the effects of sonorous vibra- 

 tions on naked gas-flames, jets of unignited gas, and of water. 

 These subjects, which Professor Tyndall has made peculiarly his 

 own, occupy the sixth lecture. As an example of the striking 

 experiments here described, and as a specimen of the graphic style 

 of the lecturer, we may quote a passage from this lecture (pp.' 240- 

 241):— 



