Atmospheric Dust

Abstract

ON Thursday, April 24, showers of discoloured rain fell at Inglewood, Sandhurst, Castlemaine, Kyneton, Daylesford, and the districts adjacent, that is to say, over an area of more than 2,500 square miles in extent. The heaviest showers—called by all who were out in them “showers of mud”—occurred at 7 o'clock p.m. and near midnight. The leaves of trees and shrubs, roofs of buildings, fences, and everything on which it could rest were more or less covered with red mud. The weather at Sandhurst for some ten days prior to this occurrence had been dry, and for a long period there had been a drought in New South Wales and in many parts northward. At several places in Victoria and New South Wales violent dust-storms occurred on the morning of the 24th immediately preceding the commencement of the rain. Some of the mud, of a bronze colour, collected by Mr. Edward Hurst of Sandhurst, was found by microscopical and chemical examination to be composed of quartz, oxide of iron, and mica; some taken from the rain-gauge stand at the School of Mines was, when dried, an almost impalpable powder of a pale reddish chocolate colour. It was seen to consist of ferruginous quartz and minute particles of black oxide of iron; and a smaller quantity collected at my private meteorological observatory—about three-quarters of a mile distant—was paler in colour, and consisted of quartz (much of it iron-free), alumina, sesquioxide of iron, and white and reddish-yellow mica. A small proportion of it was attractable by the magnet. The water collected in the rain-gauges when agitated was reddish-brown in colour, and the proportion of sediment was very large, leaving no room for doubt that the dust was brought down by the rain. Its composition and the times at which it fell lead me to believe that it came from the north and had travelled far.