76 Notices respecting New Books. 



" The most marvellous flame hitherto discovered is now before 

 you. It issues from the single orifice of a steatite burner, and reaches 

 a height of 24 inches. The slightest tap on a distant anvil reduces 

 its height to 7 inches. When I shake this bunch of keys the flame 

 is violently agitated and emits a loud roar. The dropping of a six- 

 pence into a hand already containing coin, at a distance of 20 yards, 

 knocks the flame down. I cannot walk across the floor without 

 agitating the flame. The creaking of my boots sets it in violent 

 commotion. The crumpling or tearing of a bit of paper, or the 

 rustle of a silk dress, does the same. It is startled by the patter of 

 a raindrop. I hold a watch near the flame, nobody hears its ticks ; 

 but you all see their effect upon the flame. At every tick it falls. 

 The winding up of the watch also produces tumult. The twitter of 

 a distant sparrow shakes the flame down ; the note of a cricket 

 would do the same. From a distance of 30 yards I have chirruped 

 to this flame and caused it to fall and roar. I repeat a passage from 

 Spenser : — 



' Her ivory forehead, full of bounty brave, 



Like a broad table did itself dispread 

 For love his lofty triumphs to engrave 



And write the battles of his great godhead. 

 All truth and goodness might therein be read, 



For there their dwelling was ; and when she spake, 

 Sweet words, like dropping honey, she did shed ; 



And through the pearls and rubies softly brake 



A silver sound, which heavenly music seemed to make.' 



" The flame picks out certain sounds from my utterance ; it notices 

 some by the slightest nod, to others it bows more distinctly, to some 

 its obeisance is very profound, while to many sounds it turns an en- 

 tirely deaf ear." 



The seventh lecture treats of the phenomena which result from 

 the coexistence of two or more sets of vibrations in the same me- 

 dium, namely interferences, beats, and resultant tones. 



In the eighth lecture the principles previously explained are ap- 

 plied to elucidate the physical causes of harmony and discord, and 

 the distinctive characteristics of the principal musical intervals. 

 Professor Tyndall of course adopts Helmholtz's view that rapid beats 

 are the cause of discord, and that resultant tones are an independent 

 phenomenon ; but his explanation of the different effects upon the 

 ear of resultant tones and of beats is not quite accurate. In order 

 to account for the disturbing effects of the latter as compared with 

 the perfect musical character of the former, we are told (p. 299) that 

 whereas " the impulses of ordinary sonorous waves are gently gra- 

 duated, in the beats, on the contrary, the boundaries of sound and 

 silence are abrupt, and they therefore subject the ear to that jerking 

 intermittence which expresses itself to consciousness as dissonance." 

 Very little reflection upon the way in which beats are generated, or 

 a glance at figure 145 (p. 269), is sufficient to show that the sudden 

 alternations of sound and silence here spoken of do not exist. The 



