Fuly 1, 1886] 
correspond with a more advanced stage of the spot-cycle 
than was indicated by numerical data alone. 
Signor Tacchini concludes his memoir with a survey of 
the vicissitudes of spot-formation during eight years— 
from January 1, 1877, to December 31, 1884. The results 
are graphically exhibited in a set of curves variously 
derived. No. 1 is constructed from the daily numbers of 
spots with their accompanying pores; No. 2 from the 
record of spots alone; No. 3 shows the frequency of 
groups ; No. 4 follows the fluctuations of spotted area ; 
No. 5 those of facularextension. All the first four methods 
agree in fixing the ab.olute minimum in March 1879; 
Nos 1, 2, and 3 display secondary maxima in September 
1880, March and July 1881, and March 1882: the absolute 
maximum was reached, judging by the statistics of spots 
and groups (curves 2 and 3) in February 1884; but in 
November 1883, according to those of spots with pores, 
and spotted area (curves 1 and 4). It is noticeable that 
the preliminary maxima are largely exaggerated in pro- 
portion to the true maximum, when pores are admitted 
into the account with spots ; while the curve resulting from 
the simple enumeration of groupsis very slightly indented. 
This last method is regarded by our author as that which 
should invariably be followed when recent have to be 
compared with ancient records of sunspots ; but no system 
of observation with the eye can any longer compete with 
the simpler and surer one of photographic registration. 
The curve of facular extension for 1877-84 is some- 
what anomalous. It touched its lowest point in Novem- 
ber 1878, five months previous to the spot-minimum, then 
sprang up to an absolute maximum in October 1880. 
This was followed by a secondary but very considerable 
rise in Septentber 1881, after which, during two years, a 
tolerably high average level was maintained. The 
definitive decline which set in in September 1883 
was only partially arrested in May 1884. The coincidence 
between the maximum of faculz in September 1880, and 
a large and abrupt increase in the formation of pores, 
just a month earlier, should not be overlooked. It is also 
remarkable that a maximum of prominences, but slightly 
inferior to that of 1884, occurred in 1881. 
The condition of the sun in 1885 is epitomised in the 
note by Signor Tacchini already referred to. That year 
was, in his opinion, distinguished as one of continued 
agitation by the persistent abundance of its various 
symptoms in the neighbourhood of the equator. A zone 
of 4o° north and south covered all the spots, and (save 
one example of each kind) all the facula and metallic 
eruptions observed. The tranquil or “hydrogenic” 
description of prominences, on the other hand, figured 
indifferently in all latitudes. Their general equality of 
diffusion was but slightly infringed by a southern prepon- 
derance ; while the frequency in the same hemisphere of 
spots, faculee, and eruptions was, in each class, almost 
double that of its northern occurrence. The alternating 
activity of the solar hemispheres, thus exemplified in 
one of its most conspicuous phases, is one of the many 
enigmatical features of solar disturbance. 
SEISMOLOGY IN FAPAN? 
POUNDED only in 1879, the Seismological Society 
of Japan is already able to point to a good record 
of accomplished work. The Society was happy in the 
time and the place of its birth, No home could be 
more fitted to nurse the enthusiasm of the seismologist 
than one whose foundations are shaken, on the average, a 
little oftener than once a week. One may take a rather 
half-hearted interest in other natural phenomena, but, 
while it lasts, an earthquake certainly commands undi- 
vided attention. And the Society came into being just 
when a few zealous investigators were striving who should 
* Transactions of the Seismological Society of Japa I. viii. (Tokio: 
\ Published by the Society, 1885.) 8 igh Ieleny Cr out CRE: 
NA TORE 
195 
be first to solve the problem of obtaining an accurate 
record of how the ground moves in an earthquake. Lord 
Byron has described a thunderstorm in the Alps as the 
joy of the hills “o’er a young earthquake’s birth ;” but 
the joy of the hills, if more loudly expressed, was nothing 
like so deep as the joy with which the inventor of a new 
“ earthquake machine” felt the first convulsion that came 
to test its powers. In these congenial conditions it is not 
surprising that the Society’s early volumes record the 
history of what is nothing less than a new departure in 
observational seismology. Of late the Society has suffered 
by the removal from Japan of some of its more active 
members ; but this latest volume of its 7yavsactions gives 
satisfactory evidence that, while it has not yet lost all its 
foreign supporters, some of the Japanese themselves are 
ready to step forward and continue the work. So long 
as Prof. Milne remains, the Society will not lack material 
for publication ; the present volume, like many of its 
predecessors, is largely the work of his pen. 
The first paper, on ‘‘ Seismic Experiments,” is by Mr. 
Milne, and contains an account of eight series of experi- 
ments on artificial earthquakes, as well as some labora- 
tory work. Part of this work was done in conjunction 
with Mr. T. Gray, and much of it has already been 
described in other papers. The vibrations of the ground 
were produced in some instances by letting fall heavy 
weights, in others by the use of dynamite. Several 
observing-stations were selected, at various distances 
from the source of disturbance, and generally in one 
straight line with it. At these stations seismographs of 
various kinds were placed, and Prof. Milne seems to 
have preferred the horizontal pendulum seismograph of 
the present writer as an instrument for recording sepa- 
rately two rectangular components of the horizontal 
motion of the ground. By placing the pair of pendulums 
so that one recorded vibrations in the direction of the line 
joining the station with the source, while the other 
recorded vibrations at right angles to this, Prof. Milne 
was able to separate without difficulty the normal from 
the transverse constituents of the disturbance, and to see 
the normal vibrations arrive sooner than the transverse 
vibrations at each station, as the theory of waves in elastic 
solids requires. In this instrument the two components 
of horizontal motion are separately recorded on a moving 
plate of smoked glass. Another instrument was used 
to record the whole horizontal movement on a fixed 
plate, and, as might be expected, the diagrams it 
gave showed first a movement in the line of the source, 
quickly followed by a confused wriggle of vibrations in 
all azimuths. By telegraphically connecting the moving 
plates of the horizontal pendulum seismographs, Prof. 
Milne endeavoured to determine the interval of time 
between the arrival of the disturbance at successive sta- 
tions, and so to infer the velocity of transit. From the 
results he has concluded that the velocity decreases as 
the disturbance travels away from the origin, but the 
figures on which this conclusion is based seem to the 
present writer to furnish very insufficient evidence. In 
one series of experiments there is, in the average of three 
pairs of observations, a loss of about 6 per cent. in the 
velocity between the second and third stations as com- 
pared with the velocity between the first and second 
stations ; but, when we examine the individual observa- 
tions, we find in one case a gain of velocity amounting 
to 14 per cent. And, on turning to what is apparently 
the most complete series of automatically-recorded dia- 
grams (which are reproduced in lithographed plates), it is 
clear that the time-intervals cannot have been measured 
with the precision necessary to establish this result, still 
less to justify the further conclusion that the velocities of 
normal and transverse waves become more nearly equal 
asthe disturbance spreads. The velocity of transit is, in 
fact, a term of very vague meaning, unless we can follow 
an individual wave along its course. As Mr. Milne’s 
