AUGUST 31, 1899] 
NATURE 
431 
on Lake Nyassa was determined by exchanges of signals between 
this station and the Observatory, made by Captain Close, R.E., 
and Dr. E. Kohlschutter. The adopted value for the longi- 
tude of the station occupied (which was 5°2s. west of the Bay) 
was 
2h. 17m. 7°6s. E., 
and thus the previously accepted longitude was about six miles 
in error. This work was undertaken in connection with the 
delimitation of the Anglo-German boundary between Lakes 
Nyassa and Tanganyika. 
Longitude of Umtali.—Similar operations undertaken by 
Captain Watherstone, R.E., in connection with the Anglo- 
Portuguese Barué Delimitation Commission, gave the longitude 
of Umtali as 2h. rom. 412s. E. 
Time Service.—The usual distribution of time signals for 
commercial and navigation purposes has been carried out. 
PROF. F. OMORI ON EARTHQUAKE-MOTION. 
“THREE important memoirs have recently been published by 
Dr. F. Omori, Professor of Seismology at the Imperial 
University of Tokio.! In the first he describes a form of 
horizontal pendulum adapted for mechanical registration, a 
method which, like the Italian seismologists, he prefers on 
account of its cheapness and the more open diagrams which it 
provides. The pendulum consists of a thin brass cylinder, filled 
with lead, and weighing about 14 kg. This is attached to a 
horizontal tubular strut of iron, which ends in a sharp conical 
steel point, working in a conical steel socket fixed to the wall of 
an earthquake-proof house. A fine steel wire connects the 
heavy-bob with a triangular steel prism, whose knife-edge works 
in a steel V-groove mounted on a projection from.the upper part 
of the wall. The vertical distance between the points of 
suspension and support is 24 metres, the horizontal distance 
being, as usual, very small. The length of the strut from its 
pivot to the axis of the cylinder is one metre. The complete 
period of vibration is at present 28 seconds in one pendulum, 
and 17 seconds in the other. The record is made by a light 
pointer, connected at one end with the cylinder and turning 
about a vertical axis working in a stirrup rigidly connected with 
the ground. At the end of the longarm is hinged a light triangular 
writing index, the point of which rests on smoked smooth 
paper, which is wrapped round a light wooden drum, 942 mm. 
in circumference, and revolving once an hour. While the 
Italian seismologists endeavour, as a rule, to render their instru- 
ments sensitive by using a heavy steady mass, Prof. Omori 
attains the same end by reducing the friction between the parts 
of the machine ; for instance, the pressure of the writing index 
on the smoked paper isonly mgm. Prof. Omori also describes 
a portable form of the pendulum, in which the dimensions and 
heavy mass are smaller, and the points of suspension and support 
are connected with a cast-iron stand. The paper is illustrated 
by some interesting typical diagrams given by the pendulums of 
pulsatory oscillations and earthquake disturbances of neighbour- 
ing and distant origin. 
It is well known that most earthquakes begin with a pre- 
liminary tremor, consisting of vibrations whose amplitude is 
very small and whose period is generally very short. When 
the origin of the earthquake is distant, the duration of the 
tremors, as noticed by Prof. Milne and others, increases with 
the distance of the observing station ; and a similar relation, as 
Prof Omori points out in his second paper, is evident from an 
examination of different seismograms obtained in Japan. He 
shows that the duration of the preliminary tremor does not 
depend on the magnitude of the disturbed area of the earth- 
quake, for no difference of this kind is to be seen between the 
disastrous Mino-Owari earthquake of 1891 and its five strongest 
after-shocks. He finds, moreover, that, for great earthquakes 
originating at distances between 100 and 1000 km., the 
duration increases by 15 seconds for every increase of 100 km. 
in the distance from the origin. The duration of the tremor 
being ascertained at two or more stations, it is thus possible to 
determine the position of the epicentre; and, in two cases 
1 (1) “‘ Horizontal pendulums for registering mechanically earthquakes 
and other earth movements”: Journ. Coll. Sci., Linp. Univ., Tokio, vol. xi. 
1899, pp- 121-145; (2) “‘ Note on the preliminary tremor of earthquake- 
motion ’’: 2ézd., pp. 147-159 ; (3) ‘‘ Earthquake measurementat Miyako” : 
z5id., pp. 161-195. 
NO. 1557, VOL. 60] 
which are given the results agree closely with those obtained 
from isoseismal lines. Prof. Omori remarks that the approx- 
imate variation of the duration of the early tremors with the 
distance from the origin can be explained by assuming the 
existence of two sets of waves, which, starting simultaneously, 
are propagated with different velocities. The mean velocities 
for the Mino-Owari earthquake of 1891 and the Hokkaido 
earthquake of 1894 are 2°2 km. per sec. for the preliminary 
tremors and 1°7 km. per sec. for the principal waves. 
The third paper, written in conjunction with Mr. K. Hirata, 
is a valuable discussion of the earthquake measurements made 
at Miyako from June 1896 to June 1898. The observatory, 
which contains a Gray-Milne seismograph, is situated on a 
small promontory of palzeozoic rocks (in lat. 39° 38’ N. and 
long. 141° 59’ E.), and the records may therefore be regarded 
as good illustrations of earthquake measurements in a rocky 
district. Of the twenty-five earthquakes which form the 
principal subjects of the discussion, six originated in the 
mountainous regions to the west, and the remaining nineteen: 
under the Pacific Ocean, the point one degree east of Miyako 
being the most active centre of the earthquakes which disturb. 
the eastern part of Northern Japan. The authors arrive at the 
following important conclusions. As a general rule, the dura- 
tion of an earthquake seems to vary directly as the magnitude 
of the disturbed area and inversely as the distance of the 
observing station from the origin. The average duration of 
the vertical component is about four-fifths that of the horizontal 
component. The period of the maximum movement, both 
horizontal and vertical, ranges between 0°53 and 1°7 seconds 
for slow undulations, and between c*12 ard o'rs second for 
ripples. The average period of the horizontal slow undu-~ 
lations is approximately constant in the principal and end. 
portions of an earthquake, while that of the ripples is slightly 
greater during the principal portion than during the preliminary 
tremors and end portion. It is remarkable that the average 
period of ripples is roughly constant in all the earthquakes 
here considered, never varying much from one-tenth of a 
second. The range of the vertical motion was invariably less 
than that of the corresponding horizontal motion, the maximum 
vertical motion being on an average one-fifth of the maximum 
horizontal motion ; and this is true both for ripples and slow- 
undulations. The direction of the maximum earthquake 
movement, as a rule, is coincident with the direction of the line 
joining the observing station to the centre. In two earth- 
quakes (those of February 7 and April 30, 1897), the angle of 
emergence can be ascertained as well as the position of the 
epicentre, and from these data the focal depths are found to be 
15 and 9 km. respectively. 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE 
Mr. A. W. BRIGHTMORE has been appointed professor of 
engineering construction and surveying at the Royal Indian 
Engineering College, Cuoper’s Hill. 
ALL particulars referring to the technological examinations 
conducted by the City and Guilds of London Institute, and the 
regulations for the registration and inspection of classes in 
technology and manual training, will be found in the officiak 
‘*Programine”’ just published by Messrs. Whittaker and Co. 
The syllabuses of the seventy different subjects, with the list of 
works of reference in each, and the examination papers set 
this year, should prove of service both to teachers and students 
of technology. 
THE ninth summer meeting of University Extension Students 
in Oxford terminated on Wednesday, August 24. The meeting 
was throughout uniformly successful. It was divided, as usual, 
into two parts, the first part terminating on August 9. The 
number of visitors to the meeting amounted to about 1000. Of 
these considerably over 100 came from Germany and the United 
States, other nationalities being fairly well represented. The 
historical period selected for study was the nineteenth century 
from 1837, and the scientific section of the meeting was therefore 
necessarily occupied with the more important results obtained 
during that period. The lectures were well attended and 
excited considerable interest. In Part I., Prof. Gotch gave two 
lectures on ‘f The physiology of sensation,” Mr. G. C. Bourne 
two on ‘‘ The growth of the living organism,” and Prof. H. A, 
