548 Scientific Proceedings, Royal Dublin Society. 
The dust particles themselves may have originated in salt spray 
from the ocean, carried up in equatorial regions, and from which 
the heat of the sun has evaporated the water. Consequently, a 
cloud may consist of moist crystals of salt; and by the accumula- 
tion of more water upon the nucleus or salt crystal, it may become 
a minute drop, consisting of a solution of salt. This may 
condense a still larger proportion of water, and become a drop of 
rain, and that this is the case there is evidence in the fact that 
rain-water always contains sodium chloride; but a drop of rain 
does not generally contain any appreciable solid nucleus in- 
soluble in water, when the clouds from which it fell are travelling 
with our prevailing winds. Atmospheric dust may thus be said 
to be of two kinds, that which is soluble, and that which is 
insoluble in water. 
Let us deal now with that which is insoluble. 
At Palermo, on March 10th, 1901, a dense lurid cloud hung 
over the town, the sky appearing blood-red. ‘There was a strong 
south wind, and drops of rain fell, having the appearance of 
blood.’ 
The phenomenon was attributed in that locality to red dust, 
carried up from the sands of the Sahara.” 
At Naples showers of sand fell while the sky was of a deep 
red colour. 
From Algiers, reports of a similar occurrence in North 
Africa were received. 
Fine sand carried to a great height in the atmosphere is 
sustained by reason of the viscosity of the air and the minute 
dimensions of the particles. The condensation of moisture upon 
them increases their size and weight, and causes their descent as 
rain; otherwise they settle down more slowly, and travel farther 
by the operation of air currents. | 
Hellmann and Meinardus have shown the hours at which red 
and grey sand showers fell in North Germany, which came from 
the same source as that in Southern Europe.? 
Several analyses have been made, and also examinations with 
the microscope, with the result that the dust was shown to contain 
1 The Times newspaper. 2 Nature, vol. 63, p. 471. 
3 Dr. Hellmann’s Meteorologische Zeitschrift, ‘‘ Der Staubfall vom 10. und 11. 
Marz 1901.”’ 
