Page:Popular Science Monthly Volume 25.djvu/268

258 such analysis plainly can not be claimed by a department of inquiry which deals with phenomena physically demonstrable alone; be those results sound or unsound, conclusive or tentative, final or provisional, such as they are, they are the property of introspective psychology alone. Furthermore, there is a large class of psychological concepts framed on a combination of both kinds of evidence, subjective and objective.



ROFESSOR SILVANUS P. THOMPSON has made known, through the columns of "Nature," an interesting series of experiments by Professor V. Dvorák, of the University of Agram, in the production of an apparatus which should rotate under the influence of sound-waves in the same way as the radiometer introduced by Professor Crookes rotates under the influence of rays of light and heat. The same idea was suggested independently to several men, among whom were our countrymen, Professor A. M. Mayer, of Hoboken, and Mr. Edison, all of whom have made in the matter researches of great scientific interest. Professor Dvorák has devised four kinds of "sound-mills," as they may be called, two of which depend on the repulsion of resonant boxes, and two on different principles.

One of the instruments is represented in Fig. 1. It consists of a light wooden cross, balanced on a needle-point, and carrying four light resonators—hollow balls of glass, forty-four millimetres in diameter,

with an opening of four millimetres at one side, and responding to the note g', or the middle G, of the piano-forte (= 392 vibrations). When this note is forcibly sounded by the tuning-fork, the air in the 