Prof. NordensM'dld — Transport of Volcanic Dust, 293 



Some of the dust was collected and examined under tlie micro- 

 scope, and found to consist for the greater part of small, translucent 

 (or transparent), angular, uncoloured, glass-like particles, which formed 

 elongated filaments, bent sabre-fashion, or sharp-cornered flat bodies, 

 partly plain, partly connected together in the form of Y or T. The 

 filaments are commonly full of cavities, or pierced in the direction of 

 their length by hollow canals, whereby they are often light enough 

 to be able to float on water. On being examined in polarised light, 

 most of the grains of dust are found to be isotropic — that is, without 

 action on the polarisation plane of the light passing through them. 

 Only exceptionally can there be discovered under the microscope 

 doubly refracting crystalline particles, presumably of augite or 

 felspar, and non- transparent black grains of magnetic iron-ore, that 

 may be drawn out with the magnet. No traces of metallic particles 

 could be discovered in the dust by trituration in an agate mortar and 

 washing, nor did chemical reagents show the presence of cobalt or 

 nickel. 



It was clearly ascertained by the examination that the Haga dust 

 is neither a common gravel or sand dust carried by the wind from 

 neighbouring tracts, nor such a dust as that which, according to a 

 former communication made by me at a preceding anniversary, falls 

 down from the upper regions of space to the surface of the earth. 

 All showed, on the contrary, that here we had to deal with a so- 

 called volcanic ash-rain, a very common occurrence in volcanic 

 regions, but which on this occasion was remarkable on account of 

 the remoteness of our country from volcanos now in action. 



In order to have an opportunity of studying more closely this 

 natural phenomenon, a short account of it was published in the 

 newspapers, with a request that the observations which might 

 possibly have been made in regard to it in other parts of the country 

 might be sent to the Academy of Scienees. It now appeared that 

 the ash-rain observed at Haga had extended over a very wide region. 



Thus, in Stockholm two persons, who on the 30th March between 

 11 A.M. and 2 p.m. had been out of doors in the neighbourhood of 

 Gustaf Adolf's Square, had observed on their return home that their 

 face and clothes were covered with a yellowish-grey dust, which 

 could not be common dust, because the ground was wet and dirty, 

 and occasionally a little snow and rain fell from a half-clear sky. 

 The phenomenon was so striking that an account of it was given at 

 a newspaper office, where, however, it was not taken notice of, it 

 being asserted that the dust had come from some of the buildings 

 under erection in the neighbourhood. Another person observed, 

 when he crossed Ladugardsland's Square the same day at 5 o'clock 

 P.M., that a grey, ash-like dust fell, though in rather limited quantity, 

 yet so that his coat became grey from it ; a lady, who between a 

 quarter past 1 and a quarter to 4 walked between Eegeringsgatan 

 and Appelbergsgatan, found on coming home her dress covered with 

 an ash-grey powder ; a gardener at Kungsholmen unexpectedly found 

 the glass of his hot-bed frames so closely covered with a grey dust 

 that they scarcely admitted any light. Other persons made the 



