Dust Figures Research Articles

Ultrasonic Stationary Waves

THE observations described in the striking experiment of Hubbard and Loomis (NATURE, Aug. 6, 1927, p. 189) are another example of the important conclusions which may be derived from a study of the interesting phenomenon of ultrasonic stationary waves. Velocities of sound in various, liquids were determined here by the ultrasonic stationary wave method some years ago; some of these results have already been published (Trans. Roy. Soc. Can., 3, 141; 1923; 159, 191, 197; 1925; 79; 1927); others were reported to the Canadian Research Council (Report, Boyle and Morgan, 1924). The ‘detector’ of the standing waves in these experiments was ‘nodal dust figures,’ something like the figures in a Kundt's tube, but less precision was claimed for the results than is claimed by the authors above.

Calendar of Scientific Pioneers

February 24, 1799. Gearg Christoph Lichtenberg died .—The discoverer of the dust figures on electrified planes, Lichtenberg held the chair of physics at Göttingen, and in his day was well known in both Hanover and England.

On the mode of formation of dust figures on walls and ceilings

The dust figures commonly observed on walls and ceilings are grouped into two classes. Certain experiments are described showing that those of the first class are due to irregular moisture deposition on the surface caused by a corresponding irregular temperature distribution, and that those of the second class are due to deposition around obstacles caused by decreased carrying capacity of the air stream with decreased velocity.

LXXIII. Dust figures produced by electric sparks

LXXIII. <i>Dust figures produced by electric sparks</i>

The origin and growth of ripple-mark.

The object of the investigation was to determine how ripple-mark started in perfectly smooth sand, apart from accidental variations of surface friction; how the ripples grew; how the amplitude and depth of the water affected them; and whether there was any connection between ripple-mark and kindred phenomena, such as the dust figures in a Kundt’s tube. In the course of the investigation the causes, form, and mode of action of “ripple vortices” in the water were determined, and the fact that no vortices of this kind can form in a current flowing steadily in one direction over an obstacle was demonstrated, both theoretically and practically. Also many minor details came to light, such as the fact that each ripple is continually travelling, as a whole, and why it does so.

XIV. On the formation of definite figures by the deposition of dust

Owing to the kindness of Dr. W. J. Russell, F. R. S., I received in June an advance copy of his paper on the above subject. After reading this paper it appeared to me that all the figures illustrated in it could be explained on well-known principles. I shall therefore do what I can to fulfil the hope expressed by Dr. Russell at the end of his paper that physicists from his descriptions may be enabled to explain their formation. The formation of these dust figures appears to be due principally to three causes : (l) the convection currents set up by the hot plate ; (2) to gravitation ; and (3) to the repelling action of the hot surface. It seems trivial to remind the reader that gravitation plays a part in the formation of these figures, but it is to be feared that it is from not keeping the effects of gravitation fully in view that difficulty has been experienced in explaining them. It is principally owing to gravitation, or rather to an after-effect of gravitation, that no dust is deposited on certain parts of the plate. Gravitation acts on the dust under the plate as well as on the dust over it, thus causing the film of air flowing along the under surface of the plate to be dustfree, all the dust having fallen out of it.

Dust Figures of Electrostatic Lines of Force

When lecturing on Electrostatics at the Glasgow and West of Scotland Technical College, the author endeavoured to impress upon his students the identity of the laws of force for magnetism and electricity at rest. He thought it would further this idea if he could get pictures of electrostatic lines analogous to those obtained from magnets by means of iron filings, and an analysis of the difference of the conditions in the two cases led to the conclusion that there was no reason why this should not be done.When we shower iron filings upon a glass plate, or a sheet of paper, under which a magnet is placed, unlike poles are induced at the ends of each filing, and it becomes for the time being a little compass needle. Since it is very short, the total action upon it will be a couple turning it into the direction of the force at its centre, unless it be close to the magnet, in which case there will be, in addition, a translation along a line of force. This latter effect causes the filings to crowd towards the edges of the magnet.Now, in electrostatics we also have an inductive action, opposite charges being induced in the near and far ends of each particle as it comes into the field, but we have the important difference, that whereas the magnetic poles are attached to the filing and cannot be separated from it, the electric charges will leave a body if they have an opportunity of doing so.

Scientific Serials

Annalen der Physik und Chemie, January 15, No. 2, 1885.— Determination of Verdet's constants in absolute units (2 figures), by Prof. Leo Arons.—On the formation of ozone hydrogen peroxide and peroxide of sulphur (S2O7) by the electrolysis of dilute sulphuric acid (2 figures), by Franz Richarz.—Reply to some statements by F. Kohlrausch, by H. Wild.—On the method of damping for determining the ohm, by Lord Rayleigh.—On the determination of specific heats and melting points at high temperatures (11 figures and 6 tables).—Inaugural address, by Otto Ehrhardt.—Two new methods of finding the angle of polarization of metals, by H. Knoblanch (tables).—The determination of the specific heat of uranium, by Ad. Blüncke.—Experimental research on laws of the emission of light from glowing bodies (5 figures and 7 tables), by W. Möller.—Remarks on J. Fröhlich's treatise, “Kritisches zur Theorie des gebeugten Lichts,” by M. Réthy.—Observations on fluorescence, by E. Lommel.—On the double acetates of uranium (9 figures), by C. Rammelsberg.—Note on Kundt's dust figures (2 figures), by H. J. Oosting.

VI. On electrical dust figures observed on plate glass

VI. <i>On electrical dust figures observed on plate glass</i>