APRIL 14, 1904 | 
UNLAT O Fae 
571 
FIREBALLS VISIBLE IN THE SPRING 
MONTHS. 
HOUGH ordinary shooting stars are rare in the second 
quarter of the year, fireballs appear to be moderately 
numerous and to afford definite evidence of some interest- 
ing systems which, like the comets of short period, move 
in direct orbits with small inclinations. Many of these 
systems remain uncertain, and necessarily so from the 
circumstances, for fireballs are usually seen accidentally, 
and often only by persons who are unable to record them 
accurately. But every year fortunately adds something to 
our knowledge of these interesting and brilliant visitors. 
‘hey are occasionally witnessed and described by practised 
observers, their real paths computed, and the accumulated 
data now enables us to discover the special periods when 
fireballs are usually abundant and to determine the posi- 
tions of some of their principal radiant points. 
I have just completed a comparison of the dates of more 
than too fireballs (the majority of which appeared over 
England) seen during the last ten years in the spring 
quarter, and find the more prolific epochs to have been as 
under :— 
April 1-5, 8-12, and 19-22; May 2-6, 11--16, 24--28; and 
June 8-10. 
A discussion of many hundreds of fireballs observed before 
1890, which I undertook some years ago, indicated also the 
dates May 31, June 6-7 and 28-30. The June 6-7 epoch 
nearly corresponds with the more recent one of June 8-10, 
the absence of leap year in 1900 and other causes having 
probably made the date of occurrence a little later. 
Observations this year at the following epochs will be 
likely to add to our knowledge of these striking objects, and 
it is hoped they will be specially looked for during the 
earlier part of the night, for fireballs are more numerous 
during the two or three hours after sunset than at later 
times :— 
Fireball Epoch 
Apu 19-22. 
Notes 
Lyrid epoch, There will be slight moonlight. 
May 2-6, Aquarid epoch. Partial moonlight. 
May 11-16. Moon invisible. 
May 24-28. Bright moonlight. 
May 3I. ” ” 
June 6-7. No moonlight in evenings. 
June 8-10. 5D a 
June 28-30. Bright moonlight. 
The fact of there being bright moonlight at several of 
these epochs need not interfere with observation. Fireballs 
are sometimes so vividly luminous as apparently ‘‘ to put 
the moon into the shade.’’ I have occasionally seen them 
flash out with astonishing brilliancy and cause shadows, 
though the nearly full moon was shining at the time! 
In April many fine meteors diverge from Virgo and Libra, 
while in May there are Serpentids, Scorpiids and 
Ophiuchids. In June the chief radiant is in Scorpio. As 
a rule, fireballs move very slowly in long flights directed 
from radiants not far above the horizon. Whenever such 
objects are seen their paths amongst the stars should be 
carefully recorded and their durations of flight estimated. 
W. F. DENNING. 
SEISMOLOGICAL NOTES. 
A plehe periodicity of the aftershocks of the great Indian 
earthquake of June 12, 1897, is treated by Mr. R. D. 
Oldham in vol. xxxv. of the Memoirs of the Geological 
Survey of India. The principal conclusions, drawn from 
the records of the Shillong seismograph, have already been 
published in the Journal of the Asiatic Society of Bengal, vol. 
xxxi., and the present paper contains particulars of the dis- 
cussion of other records, of varying completeness, and shows 
that they confirm the conclusion already arrived at, that 
there is a tendency to a slight increase of frequency about the 
time when the horizontal tide-producing forces are varying 
most rapidly in amount and direction. The paper is illus- 
trated by a number of curves of frequency, among which we 
may specially refer to one showing the semidiurnal fre- 
quency of shocks during the half days in which the vari- 
No. 1798, VOL. 69| 
ation of tidal stress is greatest and least; the curves are 
striking as they stand, but would have been even more 
instructive had the relative frequency been calculated to 
the mean of the whole year instead of to that of each 
period. The very marked diurnal variation in frequency is 
shown to have no relation to the variations of barometric 
pressure. 
In Die Erdbeben Warte, Nos. 3, 4, 5, iii. Jahrg., 1903-4, 
Dr. A. Cancani contributes an interesting paper on the 
frequency of large earthquakes and small changes in lati- 
tude. What the author does is to examine critically, to 
extend, and to confirm results published in the seismological 
reports of the British Association (see report for 1900, p. 
107), which show that when world-shaking earthquakes 
have been frequent pole displacements have been compara- 
tively great and vice versd. For example, between 1895 
and 1902 inclusive, if we write the number of world-disturb- 
ing earthquakes in the position of numerators, and the 
corresponding pole displacements expressed in seconds of 
are in the position of denominators, we get the following 
series :— 
mol) 18 4gior'47) 7300) 27 1224 29) 
0°53 O91 07 079 072 Soe Ee 
For the first two years the earthquake records, owing to 
the small number of observing stations, are somewhat un- 
certain. The results of investigations published in the 
British Association report in 1903, which show that large 
earthquakes have also been frequent when the change in 
the direction of pole displacements was comparatively rapid, 
Dr. Cancani has apparently not had an opportunity to 
discuss. Two other papers in the same journal relate to 
the magnetic storm of October 31, 1903. In the latter of 
these, by Dr. A. Belar, references are made to a possible 
relationship between such disturbances, earthquakes, sun- 
spots, and other phenomena. 
An article on the work accomplished by Alexander von 
Humbolt in the domain of seismology and vulcanology, a 
description of the terrible shock which on January 25, 1348, 
destroyed Villach and shook central Europe, a register from 
the Laibach Observatory, and a reproduction of registers 
for May, 1903, which are largely those of stations cooper- 
ating with the British Association, together with reviews 
and notices relating to seismology, complete Dr. A. Belar’s 
useful journal. 
In No. 19 of the Publications of the Earthquake Com- 
mission of Vienna, Dr. E. v. Mojsisovics gives a general 
account of the earthquakes recorded in 1902 in the Austrian 
Empire, to which he adds an interesting note relating to 
records obtained from a pair of Wiechert’s seismographs 
established at Pribram, one of which is on the surface and 
the other at a depth of 1115 m. Both pendulums from time 
to time show pulsatory movements, but the movements 
below are less than those on the surface. 
In the records of earthquakes with distant origins the 
details of the seismograms from both instruments exactly 
agree, with the exception that the amplitude recorded under- 
ground is somewhat less than that recorded on the surface, 
which may mean that one instrument has a smaller sensi- 
bility than the other. 
No. 20 contains the earthquake register from Reubeur- 
Ehlert pendulums at Trieste, whilst No. 21 gives similar 
records from Kremsmiinster, both catalogues referring to 
1902. 
In No. 6, vol. iv., of the Bollettino della Societa sismo- 
logica Italiana, earthquake registers are brought up to the 
end of June, 1902. In the latest register issued by Strass- 
burg, which refers to June, 1903, we find the duration of 
the earthquakes recorded at Strassburg and the time of 
their commencement. In addition we find the ‘‘ commence- 
ments ’’ for teleseisms as recorded at various stations round 
the world, which for the most part are reproduced from 
the registers issued by the British Association. In the 
Laibach registers there are similar but more complete re- 
productions. The most complete reproductions, containing 
not only the times of commencement, but also times of 
certain phases of motion, duration, and amplitude, are those 
in the Bollettino. A sheet that only gives the times at which 
earthquakes have commenced has a value, but this would 
be enormously enhanced by adding other details. 
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