F eBRUARY 21, 1907] 
NATURE 
would appear on the record-receiving surface of the new 
seismograph more than a foot or 30 em. in length. It 
is, of course, possible to construct a large record receiver, 
but About a record of time, which 
probably the most important element required by the work- 
ing seismologist, nothing whatever is said. 
is it necessary ? is 
Seismographic and other Record-receiving Surfaces. 
The record receivers to which I refer are the types used 
in connection with horizontal pendulums adopted by the 
British Association, and now in use at many stations widely 
distributed round the world. Nearly all of these record on 
photographic paper moving at the rate of 
‘There are, however, one or two instru- 
ments where the paper moves at a about 250 mm. 
per hour. With very large earthquakes, the times 
commencement the commencement of the preliminary 
tremors, recorded on either the slow comparatively 
rapidly moving paper, are identical, the seismographs being 
similar and _ placed by side. With earthquakes of 
moderate intensity this is not always the case. On the 
slowly moving paper the commencement of the preliminary 
a surface of 
60 mm. per hour. 
rate of 
of 
or 
as or 
side 
tremors may be lost. The explanation apparently rests in 
the fact that slowly moving paper passing beneath two 
illuminated cross slits or an illuminated ‘* pin-hole ’’ has 
a longer exposure than that which is moving quickly. The 
longer the exposure the broader the line. In one case the 
film takes about twelve seconds to pass beneath the * pin- 
hole,’’ and in the other between two and three seconds. 
@-30 
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A 
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a ‘ 
4035 
of scientific investigation in the eyes of those critics who 
are disposed to assert that India cannot afford to be 
scientific. 
No less than 128 pages out of the 187 which comprise 
the report are devoted to the reproduction of tables giving 
the results of magnetic observations, which are further 
illustrated by a map showing the stations of observation 
of the magnetic survey. Since the year 1901, these have 
been carried practically over the whole peninsular area 
A description 
used 
with the exception of the Central Provinces. 
of some of the stations the instruments 
pletes the narrative, but no general deductions are made, 
nor is any indication afforded as to the practical result of 
these undoubtedly valuable observations. 
Major Conyngham’s report on the pendulum observations 
for determining the force of gravity is directly interesting. 
The latest instrumental equipment for this class of observ- 
ation includes “‘ half-second ’’ pendulums, which are only 
one-quarter the length of those previously used in the de- 
partment. A new method (an Austrian invention) has also 
been introduced for registration of the coincidence of beat 
and of com- 
between the free pendulum and the clock pendulum, the 
pendulums being no longer swung in vacuo. A consider- 
able increase in accuracy of observation has thus been 
assured, further refinements being introduced in the correc- 
tions applied for the minute vibrations (or wagging ’’) 
of the stand on which the instrument is fixed, due to the 
swing of the pendulum. Some of the results are curious. 
r3e 
4 
Amt VT an: 13.) mre 
- igae ws, Ib-ones 
CO OR ee ce se 
In either when the boom of the pendulum, which at 
its outer extremity carries the equivalent of a ‘* pin-hole,’’ 
the film 
case, 
is steady, we get a straight line on moving 
beneath the same. Very slight movements of the boom, 
however, are to be seen on the film which has passed 
quickly beneath its spot of light which cannot be seen on 
the film which has moved slowly. On the latter minute 
ripples have been eclipsed in the broadened line. The 
meaning of this, not only to practical seismologists, but 
to all who have to deal with photographic recording 
apparatus, is that the best result which can be obtained 
from a given instrument largely depends upon the speed 
of the photographie record-receiving surface. 
Joun MILnNe. 
SCIENCE IN INDIA} 
HE ‘narratives’? from which extracts have been 
taken for publication in the report before us are 
those of officers of the Indian Survey Department who are 
employed on work of scientific investigation. There is 
little of topographical, and nothing of geographical, interest 
in them if we except certain results derived from Captain 
Wood’s mission to Nepal. They afford, however, most 
convincing proof of the strenuous nature of the work of 
the scientific branch of the department, and should serve 
amply to justify the maintenance of a well-matured system 
1 “Extracts from Narrative Reports of Officers of the Survey of India 
for the Season 1903-04."’ Pp. 187. (Calcutta.) 
NO. 1947, VOL. 75] 
he Valparaiso Earthauake 
Suzi St 17 ls 
For instance, it was found at Calcutta that the perpetual 
tremor, or vibration, set up by traffic, due to the nature 
of those alluvial deposits on which the, city may be said 
g, absolutely negatived the value of the observ- 
ations, whilst, on the other hand, observations taken at 
to be floating 
Colaba, in Bombay, were not affected appreciably by the 
firing of the big guns of the fort in their vicinity. 
The value of *‘ g”’ (force of gravity) being used to de- 
termine the figure of the spheroid and the density of the 
earth’s crust, it was found at Colaba that the of 
attraction indicated by the observations equalled that which 
would be accounted for by a disc of earth matter below 
excess 
the instrument 2530 feet thick with an excess of density 
equal to 2-8 above the average of surface density. At 
Dehra Dun, on the other hand, the defect in ‘* g *’ indicated 
a deficiency in density of 2-8 extending to 2930 feet in 
depth. Assuming that the surface density is 2-8, this 
means that we must imagine a cavity 2930 feet deep 
under Dehra Dun; in other words, “‘ the matter under- 
lying Dehra Dun is so deficient in density—we do not 
know to what depth this deficiency may extend—that it 
would have to be pressed downwards until the surface of 
the land was 2930 feet below its present position before it 
would attain the average density of the crust of the earth. 
Likewise at Colaba an expansion of the underlying strata 
until a_ hill feet high had been formed would be 
requisite to reduce the excessively dense rock that is found 
here to the average density of 2-8.” 
Certain levelling operations referred to in anol er. part 
of the report have been undertaken in the interests of these 
2500 
