40 
It was found that ‘‘ both the sediment and the 
volcanic ash contained, (1) small, transparent, 
glassy particles; (2) brownish, half-transpar- 
ent, somewhat filamentous little staves; and 
(3) jet black, sharp-edged, small grains re- 
sembling augite. The average size of the par- 
ticles observed in the sediment was of course 
much smaller than that of the constituents of 
the ash. These observations fortify us in our 
supposition, expressed above, that the ashes of 
Krakatoa have come down in Holland.’’ 
These analyses certainly tend to confirm the 
volcanic hypothesis, though it is interesting to 
note that some of the substances found by Mr. 
McPherson are also characteristic of meteoric 
matter. The evidence thus far accumulated 
seems to point positively to the truth of the 
volcanic hypothesis. ‘The opponents of this 
view dwell upon the improbability of so much 
matter being thrown up to such a great height, 
and of its remaining so long a time in the 
atmosphere. But the magnitude of the Java 
eruption has certainly not been overrated ; 
and the amount of material thrown into the 
atmosphere from this source alone is probably 
sufficient to account for the observed effects. 
If we add the amount from the Alaskan yol- 
cano, there is less reason to doubt the ability 
of the hypothesis to account for the quantity 
of material required. The objection on the 
ground of the persistence of the phenomenon 
has been met by Messrs. Preece and Crookes 
on electrical grounds. If the matter thrown 
up is charged with negative electricity, it would 
be repelled from the earth, and its particles 
would repel each other, thus causing the rapid 
dissemination of the material in the atmos- 
phere, and its retention for an indefinite 
period. The decline of brilliancy has been 
slow during the time it has been observed in 
this country. In the Hawaiian Islands it is 
still a marked phenomenon, after a lapse of 
several months. We may therefore expect 
that for some time to come we shall observe 
it under favorable weather conditions, but that 
it will gradually become less prominent until it 
is known only as a fact of past history. 
W. UPpron. 
Washington, D.C., Jan. 1, 1884. 
WHIRLWINDS, CYCLONES, 
NADOES.1—VII. 
WE are now prepared to consider and ex- 
plain the actual distribution and motion of 
cyclones. 
The limitation of violent cyclones to the 
1 Continued from No. 45. 
AND TOR- 
SCIENCE. 
[Vou. IIL, No. 49. 
ocean is natural enough: the level surface of 
the sea allows a great accumulation of warm, 
moist air before the upsetting begins, and per- 
mits the full strength of the winds to reach a 
very low altitude. On land the air never waits. 
so long as it may at sea, before upsetting; it 
never becomes so moist; and, when in motion, 
the inequalities of hill and valley hold back the 
lower winds by friction. On land the strong 
part of the cyclone is relatively higher than at 
sea, as the records of mountain observatories 
show; and we know less of it. 
No violent cyclones are known to have oc- 
curred within four hundred miles of the equa- 
tor. Here, —where the air is warm, quiet, and 
heavily charged with moisture; where heavy, 
quiet rains are frequent ; where the conditions 
which have been mentioned as essential for 
starting a cyclone are of common occurrence, 
— cyclones are nevertheless unknown. They 
occur often enough, however, in the embry- 
onic form of thunder-showers, but they never 
reach the adult stage; and this must be be- 
cause at the equator the deflective effect of 
the earth’s rotation is zero, and the inrushing 
winds are allowed to move directly toward the 
low-pressure centre and fill up the depression, 
instead of increasing it by their deflection and 
their centrifugal force. From this we learn, 
that, while warmth and moisture may be suffi- 
cient to begin a cyclone, they alone cannot main- 
tain it. There would be no violent cyclones 
if the earth stood still. 
It might be inferred from this that cyclones. 
should increase in frequency and intensity as 
we recede from the equator toward the poles, 
for in the higher latitudes the earth’s deflective 
force is known to increase. It is true that 
storms are much more frequent in high lati- 
tudes than near the equator; and this is very 
likely due to the greater ease with which mod- — 
erate indraughts are here deflected so as to pro- 
duce a central baric depression. But the more. 
intense storms are all within thirty or thirty- 
five degrees of the equator, because, in more 
polar latitudes, the air is not warm or moist. 
enough to co-operate effectively with the deflec- 
tive forces, and produce violent winds. It has 
already been explained that a rising column of 
moist air cools more slowly than one of dry air ; 
and on this there was shown to depend much of 
the greater energy of oceanic storms over that. 
of desert whirls. It should now be added, 
that, of two ascending currents of saturated 
air, the warmer will rise much more vigorously 
than the cooler: hence the warm, saturated air 
of the tropical sea breeds hurricanes, cyclones, 
and typhoons of greater strength than be 
