190 Mr. J. Cottrell on the Division of a Sound- Wave [Feb. 12, 



merited upon. The contractions of the heart were more frequent after 

 alcohol during complete rest, from five to ten beats per minute for some 

 time ; and when exercise was taken the increase was greater. The mean 

 pulse of the twenty-four hours was, however, not increased unless the 

 amount of alcohol was large and repeated. In other words, the heart's 

 beats were less frequent than natural when the effect of the alcohol had 

 passed off. The pulse became both fuller and softer to the touch ; and this 

 relaxation of the radial artery was shown also by the sphygmograph. That 

 the smaller vessels were relaxed, was shown both by the redness of the 

 surface and by the evident ease with which the blood traversed the capil- 

 laries, as shown by the sphygmographic tracings. 



6. The respirations were not increased in number by alcohol ; they 

 were rather lessened, and were deeper in some of the experiments ; but 

 the effect was not very marked. 



III. " Experimental Demonstrations of the Stoppage of Sound by 

 partial Reflections in a non-homogeneous Atmosphere/' By 

 JOHN TYNDALL, D.C.L., LL.D., F.R.S., Professor of Natural 

 Philosophy in the Royal Institution. 



(See Paper read Jan. 15, ante.) 



IV. " On the Division of a Sound- Wave by a Layer of Flame 

 or heated Gas into a reflected and a transmitted Wave." By 

 JOHN COTTRELL, Assistant in the Physical Laboratory of the 

 Royal Institution. Communicated by Professor TYNDALL, 

 F.R.S. Received February 2, 1874. 



The incompetency of a sound-pulse to pass through non-homogeneous 

 air having been experimentally demonstrated by Dr. Tyndall, and proved 

 to be due to its successive partial reflections at the limiting surfaces of 

 layers of air or vapour of different density, further experiments were 

 conducted in order to render visible the action of the reflected sound- 

 wave. 



The most successful of the various methods contrived for this purpose 

 consists of the following arrangement. A vibrating bell contained in a 

 padded box was directed so as to send a sound-wave through a tin 

 tube, B A (38 inches long, l|inch diameter), in the direction BF', its 

 action being rendered manifest by its causing a sensitive flame placed at 

 F' to become violently agitated. 



The invisible heated layer immediately above the luminous portion of 

 an ignited coal-gas flame issuing from an ordinary bat's- wing burner 



