URING 1938 two series of observations on the propagation of sounds in the open air were reported. Kukkamaki carried out measurements D of the velocity of sound over tracts of 1 km. in Finland, one series over land and two over a lake, f i s t in suminer and then in minter when the lake was frozen. The three sets gave speeds-reduced to 0 ' C. and absence of humidity or carbon dioxide-which differed by less than 0.1 per cent and had a mean value of 330.79 m./sec. The effect of r i n d was eliminated in the customary manner, by taking the average of forward and return excursions of the sound pulse, which was produced by the firing of a l-kg. bomb at 1 m. above the ground. On the other hand the work of Waetzmann," Scholz and Kruger is concerned with the dissipation in the atmosphere of aeroplane noises. A n aeroplane passed at various heights in horizontal flight over a microphone so that the sound intensity could be recorded when it was exactly overhead. From these data an intensity :height curve was plotted. Atmospheric losses were indicated by departures from the parabola which an inverse square law T o d d give. These were attributed to the water vapour and carbon dioxide in the atmosphere. Apart from increased decrement, the curve for a humid day did not indicate any abnormality in propagation.Colwell, Friend and McGraw (3) describe an apparatus which should be of use in a senior school or university laboratory. A glow-discharge valve working in a simple circuit off the-1.C. mains (60 c.jsec.) causes a series of short pulses a t the same frequency t o be emitted from a loud-speaker. At a short distance along the bench is a microphone from which the current is led to the vertical pair of plates of a cathode-ray oscillograph while the sweep circuit of the instrument sweeps the electron spot from left to right at the same rate of 60 times a second. The sound pulse when picked up appears as a vertical jag in the horizontal line traced by the spot on the screen, and the position of this jag is governed by the relative epochs of emission and arrival of the pulses. The distance that the microphone must be moved between two stations that give the jag in the centre of the oscilloscope screen is equal t o the wave-length of a 60 c.jsec. tone in the air of the laboratory, so that the experiment takes up five or six metres of bench space, but this can be reduceg, at the loss of a little accuracy, if the emitting circuit is arranged to give harmonic pulses of the driving frequency.* The science of acoustics has suffered a grievous loss by the deaths, within a few months of each other, of two professors who devoted their lives to research in this subject, E.Waetzmam of Breslau and Xax W e n of Jena ; and of a younger physicist of great promise, J. E. R. Constable Qf the Xational Physical Laboratory.
