Under the first head Dr. Mott stated that all experiments and photographs made to establish the existence of sound waves simply referred to the necessary agitation of the air accompanying any disturbance, such as would of necessity be produced by a vibrating body, and had nothing to do directly with sound. He stated that in the Edison telephone, sound was converted directly into electricity without vibrating any diaphragm at all, as attested to by Edison himself. Speaking of the mobility of the air, he said the particles were free to slip around and not practically be pushed at all, and that the greatest distance a steam whistle could affect the air would not exceed 30 feet, and the waves would not travel more than 4 or 5 feet a second, while sound travels 1,120 feet a second. Under heat and velocity of sound waves, Dr. Mott stated that Newton found by calculating the exact relative density and elasticity of air that sound should travel only 916 feet a second, while it was known to travel 1,120 feet a second.
Laplace, by a heat and cold theory, tried to account for the 174 feet, and supposed that in the condensed portion of a sound wave heat was generated, and in the rarefied portion cold was produced; the heat augmenting the elasticity and therefore the sound waves, and the cold produced neutralizing the heat, thus kept the atmosphere at a constant temperature. Dr. Mott stated that when Newton first pointed out this discrepancy of 174 feet, the theory should have been dropped at once, and later on he showed the consequences of Laplace's heat and cold theory.
The great argument of the evening, and the one to which he attached the most importance, was that all scientists have spoken of the swift movement of the tuning fork, while in fact it moved 25,000 times slower than the hour hand of a clock and 300,000,000 times slower than any clock pendulum ever constructed.
Since a pendulum cannot, according to the high authorities, produce sonorous air waves on account of its slow movement, Dr. Mott asks some one to enlighten him how a prong of a tuning fork going 300,000,000 times slower could be able to produce them. He then showed that there was not the slightest similarity between the theoretical sound waves and water waves, and still they are spoken of as "precisely similar" and "essentially identical," and "move in exactly the same way." Considerable merriment was occasioned when Dr. Mott showed what a locust stridulating in the air would be called upon to do if the present theory of sound were correct. He stated that a locust not weighing more than half a pennyweight, and that could not move an ounce weight, was supposed capable of setting 4 cubic miles of atmosphere into vibration, weighing 120,000,000 tons, so that it would be displaced 440 times in one second, and any portion of the air could bend the human tympanic membrane once in and once out 440 times in one second; and that 40,000,000 people, nearly the whole population of the United States, could have their 5,000 pounds of tympanic membrane thus shaken by an insect that could not move an ounce weight to save its life; and that the 231,222 pounds of tympanic membrane of the entire population of the earth, amounting to 1,350,000,000, who could conveniently stand in 11¼ square miles, would be affected the same way by 34 locusts stridulating in the air. According to the barometric theory of Sir William Thomson, he showed that a locust would have to add 60,000,000 pounds to the weight of the atmosphere.
Under elasticity and density he stated that elasticity was a mere property of a body, and could not add one grain of force to that exercised by the locust, so as to assist it in performing such wonderful feats. Under interference he showed that the law of interference is fallacious; that no such thing occurs; and that in the experiment with the siren to show such fact, the octave is produced which of necessity ought to be when the number of orifices are alternately doubled, and the same effect would be produced with one disk with double the number of holes. Under the last head of his paper Dr. Mott proved that the membrana tympani was not necessary for good hearing, that in fact when it was punctured, a deaf man could in many cases be made to hear, and in fact it improved the hearing in general; the only reason why the tympanic membrane was not punctured oftener was that dust, heat, and cold were apt to injure the middle ear.
In closing his paper Dr. Mott said that he would risk the fallacy of the current theory of sound on the argument advanced relating to the impossibility of the slow motion of a tuning fork to produce sonorous waves, and stated that he would retire if any one could show the fallacy of the argument; but if not, the wave theory must be abandoned as absurd and fallacious, as was the Ptolemaic system of astronomy, which was handed down from age to age until Copernicus and his aide de camp Galileo gave to the world a better system.
THE ATTOCK BRIDGE.
We give illustrations from Engineering of a bridge recently constructed across the Indus River at Attock, for the Punjaub Northern State Railway. This bridge, which was opened on May 24, 1883, was erected under the direction of Mr. F.L. O'Callaghan, engineer in chief, Mr. H. Johnson acting as executive engineer, and Messrs. R.W. Egerton and H. Savary as assistants.