250 ANNUAL OF SCIENTIFIC DISCOVERY. 



ON A NEW AND SINGULAR ACOUSTIC PHENOMENA. 



At tlic Dublin meeting of the British Association, Mr. Donovan, in a com- 

 munication, first explained the beats which are experienced when two strings 

 tuned nearly, but not exactly, to unison, are struck at the same time. He 

 then stated that the Earl Stanhope had observed that when a tuning fork 

 whilst vibrating was held to the teeth, similar beats were heard, which he, 

 Earl Stanhope, attributed in the two prongs of the tuning fork not being in 

 exact unison. This effect the author often tried to experience, but never 

 could succeed until upon one occasion, just after he had ceased from violent 

 exercise, having applied the fork to his teeth, he distinctly heard the beats. 

 He was thus led to the true origin of the phenomenon, which he could now 

 experience whenever he wished by running a short distance, particularly up 

 and down stairs. The effect was caused by the beatings of his own heart, 

 or the pulsations of the circulating blood. Some authorities however, would 

 explain the phenomenon described by the author, to one set of vibrations 

 propagated to the auditory nerve through the bones of the teeth, and of the 

 head, modified by the action of the heart interfering with other pulses propa- 

 gated in the ordinary way through the air to the organ of hearing. 



VIBEATIONS OCCASIONED BY WATER FALLING OVER DAMS. 



At the Montreal meeting of the American Association for the Promotion 

 of Science, Professor Snell of Amherst, presented a communication on the 

 vibrations occasioned by the water falling over the dam across the Connecti- 

 cut river at Had ley and Holyoke, Mass. 



He first described the dam as a structure 1017 feet in length and thirty 

 feet high, over which, at the time of his observations, about two feet of 

 water was falling in an unbroken sheet. By descending to the base of the 

 dam and looking behind the sheet of water, the currents of air rushing in and 

 out could be perceptibly felt. These currents were set in motion by the 

 water, and were vibratory. The action of the water produced rarefication, 

 which in turn produced the pulsatory motion of the sheet, the smallncss 

 of the space not being sufficiently large to allow a current through the entire 

 length. These vibrations varied ; when the thermometer was at eighty, and 

 the water two feet in depth, the vibrations were 137 per minute. When the 

 temperature was at seventy, the vibrations were 130. 



The vibrations were in two segments, alternating with each other gcner- 

 allv, and were sufficient at times to throw the sheet of water at its base ten 



/ ' 



inches outward, produced, he did not doubt, by the pressure of the air be- 

 hind. They were communicated to the ground, and were of sufficient force 

 at times to be felt at Springfield, eight miles distant, pulsating the windows 

 and doors at the same rate, 137 per minute ! 



Professor Hitchcock endorsed the view presented, and said that he had 

 repeatedly seen the vibrations from a hill four miles distant, and it was a 

 most beautiful sight. 



Mr. Charles Stodcler of Boston, however, in a paper recently read before 



