442 



SCIENCE 



[N. S. Vol. LII. No. 1349 



ciate professor of geography in tlie University 

 of Sydney. 



DISCUSSION AND CORRESPONDENCE 



VISIBLE SOUND WAVES 



The following notes, written by Lieutenant 

 Thomas T. Mackie, 123d Field Artillery, 

 A. E. ¥., describe a phenomenon which must 

 have been observed rarely, if ever before, and 

 it seems to be very much worth while to put 

 the circumstances on record. 



On one or two occasions within recent years the 

 ooourrene© of sound waves visible to the naked 

 eye under peculiar atmospheric conditions has, I 

 believe, been reported; yet the event is so unusual 

 that I have been persuaded to describe a similar 

 one which I witnessed at the front on the opening 

 day of the Meuse-Argonne offensive. 



During the days immediately preceding the at- 

 tack my regiment moved into position in a wooded 

 area opposite Montfaucon, characterized by the 

 roughness of the terrain, a jumble of high hills 

 cut up by narrow and deep valleys. The battery 

 to which I belonged was sent into position at the 

 head of one of these valleys, enclosed by very 

 steep slopes, and having roughly the shape of a V 

 with the open end to the south. Some four or 

 five hundred yards to our rear and approximately 

 on a line with the extremities of the arms of the 

 V was a battery of six-inch rifles. 



For several days the weather had been more or 

 less rainy and wet, and the morning of Septemlber 

 26 found us covered by a very heavy bank of fog 

 which entirely excluded the sun. Soon after the 

 attack opened, I had occasion to go to the top of 

 one of the hUls which flanked our position, and at 

 a certain definite level above the battery a very 

 considerable disturbance in the fog was noticeable 

 after each discharge of the heavy rifles behind me. 

 The visibility was such that the flash of the dis- 

 charge could not be seen, but each time before the 

 report reached us a band of greater density -was 

 clearly visible in the fog, moving with great rapid- 

 ity up the valley toward us in the form of an arc. 

 Its arrival was simultaneous with that of the 

 sound of the discharge. This are of greater fog 

 density was perhaps six feet from its anterior to 

 its posterior edge, and of about the same depth. 

 It followed closely an altitude of some sixty or 

 seventy feet above the floor of the valley and was 

 clearly visible from both above and below that 

 plane, but no similar phenomena were visible in 

 any other plane. 



The recent researches of Professor D. 0. 

 Miller, and others have shown that the muzzle 

 wave from a large grm carries in its front a 

 narrow region of compression immediately 

 followed by a relatively wide region of ex- 

 pansion. From the above account, it would 

 appear that the air was saturated with water 

 vapor at a particular level, and that the 

 expansion in the wave produced a visible in- 

 crease in the fog density, the effect disappear- 

 ing immediately again, owing to the subse- 

 quent re-evaporation when the air regained 

 its normal pressure and temperature. The 

 conditions of the terrain were very favorable 

 to the concentration of a great amount of 

 energy into the wave- front, and this was prob- 

 ably assisted by a sound-mirage effect. The 

 upper layers of air being warmer than the 

 lower the sound wave-fronts would be so bent 

 as to tend to keep the energy near the earth's 

 surface. The ''experiment " was thus being 

 conducted under such circumstances and on 

 such a scale as can not readily be reproduced 

 in the laboratory, and would rarely occur 

 anywhere. 



Frederick A. Saunders 



Jefferson Physical Laboratory, 

 Harvard University, 

 October, 1920 



DRIFT BOTTLES AS INDICATING A SUPER- 

 FICIAL CIRCULATION IN THE GULF OF 

 MAINE 



In his " Explorations in the Gulf of 

 Maine " H. B. Bigelow^ has found evidence 

 of a circulation of the water in the gulf. 

 Since this evidence depends chiefly on the 

 contours of the osohalines and the distribu- 

 tion of plankton, the direction and rate of 

 movement of the drift bottles to be described, 

 obtained incidentally in another investigation 

 may be of importance in adding to this evi- 

 dence. During the summer of 1919 as part 

 of the hydrographic work in the Bay of 

 Fundy by the Biological Board of Canada, 

 330 drift bottles were set out in the bay. 

 Sixteen of these bottles have been picked up 

 on the shores of the Gulf of Maine. The 



1 Bull. Mus. Comp. Zool, Vol. 58, p. 29; Vol. 59, 

 p. 149; Vol. 61, p. 163 



