A Few Millions

Abstract

IN your reprint of Prof. Mayer's paper, entitled “Acoustical Experiments” in NATURE for May 9, 1872, there occur some strange numerical errors, which perhaps it will be well to point out, lest some of your readers should make use of the numbers given at the end of the paper without previously testing them. After describing his experiments, he proceeds:—“We will now examine the analogical phenomena in the case of light:—Let fork No. 1, giving 256 vibrations a second, stand for 595 millions of millions vibrations a second, which we will take as the number of vibrations made by the ray D₁ of the spectrum.” Taking the velocity of light as 185,300 miles per second, and the wave-length of D₁ as given by Angström, at 0.00058950 millimetres, gives 5,058,700,000,000,000 vibrations per second, or a little more than five thousand millions of millions, instead of a little less than six hundred millions of millions vibrations per second, as given by Dr. Mayer. But to proceed—“Then fork No. 3 will represent 590 millions of millions vibration per second,” this should be 594 millions of millions vibrations, “which give a wave-length .0000042 millimetres longer than D₁.” This again is not quite right, even according to Dr. Mayer's ownshowing; it should be .00000495 of a millimetre longer than D₁. Dr. Mayer then goes on to say that such a wave-length nearly corresponds with an iron line situate .42 div. below D₁ on Angström's chart; and “we saw that fork No. 3, giving 254 vibrations a second, had to move toward the ear with a velocity of 8.734ft, to give the note produced by 256 vibrations per second emanating from a fixed point; so a star sendingiforth the ray which vibrates 590 millions of millions a second will have to move toward the eye with a velocity of 28,470 miles per second to give the colour produced when ray D₁ emanates from a stationary flame.” This again, according to Dr. Mayer's own method, should be 1,557 miles, or less than a nineteenth of the velocity given by him.