ON THE PILOBOLIME. 
253 
idea of an African picture on tlie approach of the simoon, 
while opposite the full moon was rising over the lofty 
ranges against a lovely sky of a deep sea-green. The com¬ 
bined effect on houses, trees, etc., must be left to the 
imagination to portray. I am strongly of opinion that the 
Krakatoa eruption is the first cause of these wondrous pictures 
in the Kosmos ; and I think I see a way of escape from the 
difficulty re the displays appearing a fortnight later in India 
and Ceylon than in Western Africa. We must remember 
that the eruption took place in a zone of low barometer. 
Over this, apart from differences of altitude, there would be 
a relatively higher or accumulated pressure caused by the 
ascending currents. At least, such a state of matters prevailed 
at Ben Nevis during low pressure periods. Well then, the 
piercing and tearing asunder of the atmosphere over that 
mighty Javan furnace, and the force of the eruption, would be 
the means of the minute dust particles being ultimately safely 
landed on the top, as it were, of the upper high pressure. 
They would afterwards be buoyed up and play over the 
currents like the “ willow-leaves” in the sun, changing their 
altitude from time to time with barometric variations. By 
the rapid rotation of the earth at the equator an easterly 
upper current would bear the dust westwards ; and the high 
pressure above the low pressure over the Asiatic land at that 
season would not allow the dust to make much of a northerly 
course. On the other hand, the overflow of dust from the 
main westerly stream would be in a southerly direction where 
low pressure prevailed over the surface high pressure of the 
great Indian Ocean. I am hurrying for the mail, and trust I 
have sufficiently explained my meaning ; and other notes w 
re may follow m course. —Clement L. Wragge, Torrens 
Observatory, Adelaide, South Australia. July 17, 1884. 
ON THE PILOBOLIDyE, 
WITH A SYNOPSIS OF THE EUROPEAN SPECIES, AND A 
DESCRIPTION OF A NEW ONE. 
BY W. B. GROVE, B.A., 
HON. LIBRARIAN OF THE BIRMINGHAM NATURAL HISTORY AND MICROSCOPICAL 
SOCIETY. 
(Continued from page 220.) 
1 . —Heliotropism. 
The stem and swelling vary much in appearance according 
to the circumstances under which they grow. They are very 
