The Formation of Dust-ripples

Abstract

LAST evening when returning from a visit to the trenches I noticed an interesting illustration of the formation of dust-ripples. A battery of field-guns had been placed nearly parallel to a road some 2000 yards behind the lines. Owing to the continued fine weather the roadway was covered by a coating of fine dust. The guns were about 100 yards from the road, on lower ground, and pointing so that the shells just cleared. The battery had been in action all day. There was very little wind and no traffic over the road during day-time. The whole surface of the road in front of the guns was covered by a series of small ripples at right angles to the direction of the guns. The ripples were about 1/12 in. apart, from east to west. They were evidently caused by the explosive wave passing over the road. The same effect can be produced by discharging a Leyden jar across a sparkgap near a card on which some light powder has been sprinkled, or by tapping sharply a piece of parchment stretched tightly over the end of a lamp-glass containing fine powder.