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prepared a pipe and some some soap suds, for blowing bubbles, and by making a connection with the receivers I am able to inflate the bubbles with a mixture of oxygen and hydrogen.
You see with what rapidity the little balloons mount to the ceiling. I touch them with a candle and you are startled by their explosion. Doubtless most of you have seen the experiment before, and have learned that when the gaseous particles rush together, after the explosion, they are joined chemically so as to form water; but I think none of you
have ever dreamed of any possible bond of union between the explosion and satellite revolution, or of weighing the bubbles in a scale with the sun. That there is such a bond, and that the sun can be thus weighed, I will try to show you.
Tyndall has told us (op. cit., section 181) that the force of explosion, in one pound of hydrogen uniting with eight pounds of oxygen, is “equivalent in energy to the descent of a ton weight down a precipice 22,320 feet high"; it would, therefore, be sufficient to lift a ton to the top of such a precipice. If it were all concentrated upon the hydrogen alone, that gas would be driven entirely beyond the reach of the earth's attraction; but it carries with it the eight pounds of oxygen, and, notwithstanding this ninefold burden, if there were no resistance from the air, the watery vapor would be lifted more than two thousand miles before it would begin to fall to the earth again. The velocity with which it starts is more than five miles per second, or nearly one per cent. more than the velocity with which a satellite would revolve at the surface of the earth.
You have already learned that circular orbital velocity is acquired (16) by falling through half the distance to the centre; therefore the combining energy of water is more than sufficient, if it were not for the resistances of the air and of friction, to keep it in perpetual revolution. Those resistances do not destroy the motion; they merely change it into heat, electricity, magnetism, chemical affinity, molecular vibration, or some other form of cyclical oscillation.
Do you think that these harmonies are merely accidental, or that they can be so regarded with any reasonable probability? In order to remove any possible doubts upon the question, I will ask you to follow me still further.
According to the kinetic theory of gases, the particles are in perpetual motion, and the gaseous elasticity is owing to the force of
repeated collisions. You may accept or reject the theory as you please, but all the known properties of elastic fluids are such as they would be if the theory were true. It may, therefore, be safely assumed as a guide to new investigations. In subsidence from the satellite orbit of watery vapor, when the orbit velocity is increased twofold, the gravitating acceleration (17) is increased sixteenfold. Now, if we multiply this increased acceleration by the molecular velocity of hydrogen, the product is the same as if we multiply the original acceleration by the orbital velocity of the earth, so that the explosion of our soap bubbles furnishes us with all the data which are needed for weighing the sun and measuring its distance.
In order to make our approximations as close as possible, it is desirable to check, or confirm them, by finding some other harmony of a similar character. We look naturally, in the first place, to hydrogen's companion in its plunge down the mighty precipice, and we find that oxygen stands in a still closer relation to earth's velocity of rotation than that in which hydrogen stands to earth's orbital velocity. If we divide earth's equatorial circumference by the number of seconils in a sidereal day, we find that its rotating velocity is 1525-7 feet per second, which is precisely the velocity of oxygen, according to the experiments of Clausius, at the temperature of 4.8°C. This is within the limits of possible uncertainty of the temperature of water at its greatest density, the commonly accepted temperature being 4°C.
This harmony may be extended so as to include all gases through Maxwell's law of equality of gaseous vis viva.
Substituting atomic weight for gravitating acceleration, and remembering that orbital vis riva, in equal volumes, is proportioned to the gravitating acceleration, the mean velocity of hydrogen at 4.8°C. can be readily deduced from the mean velocity, at the same temperature, of any other gas of known atomic weight. If we adopt Regnault's value for the atomic weight of oxygen, 15.96, the mean distance of the sun is 92,769,000 miles ; its mass 331,595; and the velocity of light is 186,400 miles per second. These results, though so simply: deduced, are fully as trustworthy as any that astronomers have yet reached, after thousands of years of patient observation and tedious calculation. WHOLE No. Vol. CXII.—(THIRD SERIES, Vol. Ixxxii.)
MODIFICATION OF WHEATSTONE'S MICROPHONE AND ITS APPLICABILITY TO RADIOPHONIC RESEARCHES.
By ALEXANDER GRAHAM BELL. A paper read before the Philosophical Society of Washington, D.C., June, 11, 1881.
In August, 1880, I directed attention to the fact that thin disks or diaphragms of various materials become sonorous when exposed to the action of an intermittent beam of sunlight, and I stated my belief that the sounds were due to molecular disturbances produced in the substance composing the diaphragm.* Shortly afterwards Lord Raleigh undertook a mathematical investigation of the subject, and came to the conclusion that the audible effects were caused by the bending of the plates under unequal heating.† This explanation has recently been called in question by Mr. Preece, I who has expressed the opinion that although vibrations may be produced in the disks by the action of the intermittent beam, such vibrations are not the cause of the sonorous effects observed. According to him, the ærial disturbances that produce the sound arise spontaneously in the air itself by sudden expansion due to heat communicated from the diaphragm-every increase of heat giving rise to a fresh pulse of air. Mr. Preece was led to discard the theoretical explanation of Lord Raleigh on account of the failure of experiments undertaken to test the theory. He was thus forced-by the supposed insufficiency of the explanation
to seek in some other direction the cause of the phenomenon observed, and as a consequence he adopted the ingenious hypothesis alluded to above. But the experiments which had proved unsuccessful in the hands of Mr. Preece were perfectly successful when repeated in America under better conditions of experiment, and the supposed necessity for another hypothesis at once vanished. I have shown in a recent paper read before the National Academy of Science, || that audible sounds result from the expansion and contraction of the material exposed to the beam; and that a real to and fro vibration of the diaphragm occurs, capable of producing sonorous effects. It has occurred to me that Mr. Preece's failure to detect with a delicate microphone the sonorous vibrations that were so easily observed in our experiments might be explained upon the supposition that he had employed the ordinary form of Hughes' microphone, shown in Fig. 1, and that the vibrating area was confined to the central portion of the disk. Under such circumstances it might easily happen that both the supports (A B) of the microphone might touch portions of the diaphragm which were practically at rest. It would of course be interesting to ascertain whether any such localization of the vibration as that supposed really occurred, and I have great pleasure in showing to you to-night the apparatus by means of which this point has been investigated (see Fig. 2).
* Amer. Asso, for Advancement of Science, Aug. 27, 1880. # Nature, vol. xxiii, p. 274.
Roy. Soc., Mar. 10, 1881.
The instrument is a modification of the form of microphone devised in 1827, by the late Sir Charles Wheatstone, and it consists essentially of a stiff wire (A), one end of which is rigidly attached to the centre of a metallic diaphragm (B). In Wheatstone's original arrangement the diaphragm was placed directly against the ear, and the free extremity of the wire was rested against some sounding body-like a watch. In the present arrangement the diaphragm is clamped at the circumference like a telephone-diaphragm, and the sounds are con
veyed to the ear through a rubber bearing tube (C). The wire passes through the perforated handle (D), and is exposed only at the extremity. When the wire (A) was rested against the centre of a diaphragm upon which was focussed an intermittent beam of sunlight a clear musical tone was perceived by applying the ear to the hearing tube (C). The surface of the diaphragm was then explored with the point of the microphone, and sounds were obtaincin all parts of the illuminated area and in the corresponding area on the other side of the diaphragm. Outside of this area on both sides of the diaphragm the sounds became weaker and weaker until at a certain distance from the centre they could no longer be perceived.
At the points where one would naturally place the supports of a Hughes microphone (see Fig. 1), no sound was observed. We were also unable to detect any audible effects when the point of the microphone was rested against the support to which the diaphragm was attached. The negative results obtained in Europe by Mr. Preece may therefore be reconciled with the positive results obtained in America by Mr. Tainter and myself. A still more curious demonstration of localization of vibration occurred in the case of a large metallic mass. An intermittent beam of sunlight was focussed upon a brass weight (1 kilogram),, and the surface of the weight was then explored with the microphone shown in Fig. 2. A feeble but distinct sound was heard upon touching the surface within the illuminated area and for a short distance outside, but not in other parts.
In this experiment as in the case of the thin diaphragm absolute contact between the point of the microphone and the surface explored was necessary in order to obtain audible effects. Now I do not mean to deny that sound waves may be originated in the manner suggested by Mr. Preece, but I think that our experiments have demonstrated that the kind of action described by Lord Raleigh actually occurs, and that it is sufficient to account for the audible effects observed.
STORED-UP ELECTRICITY: FAURE'S SECONDARY
A few weeks since the scientific world in Paris was deeply interested by a paper read before the Société d'Encouragement de l'Industrie Nationale by M. Reynier, upon a new form of battery invented