176 REPORT— 1899. 
7. Bombay: Colaba. Abstract from Report by N. A. F. Moos, Esq., Director of 
the Government Observatory. 
The instrument at the Bombay Government Observatory is installed 
in a small isolated building 10 feet square and 14 feet up to the eaves, 
which was formerly used for electrostatical observations. It has a gable 
roof, and is well ventilated on all sides. On the west side, at a distance 
of 40 feet, is a carriage drive leading to the Directors’ quarters, and at a 
distance of 70 feet in the same direction, and parallel to the drive, is the 
main road outside the Observatory compound. On the east side, there is 
toa distance of 60 feet open ground as far as the thermograph shed, 
beyond which an open tract continues to the sea. On the north side 
there is a small well and open ground for 120 feet, where the observers’ 
quarters are situated. Probably in consequence of a copious ventilation, 
no troubles have been experienced with the so-called earth tremors. 
The pier is oriented N.S. and E.W., and located in the centre of the 
room. Its foundation was dug 5} feet below the flooring of the room, 
which is 1} feet above the ground. At this depth a huge boulder was 
struck, upon which was laid a bed of concrete 5 x 5 feet square and 2 feet 
deep. Over this a mass of rubble masonry 4 x 4 feet and 15 feet thick 
was built, and upon this a brick pillar 15 feet square and 55 feet high, 
On the top of this there is 1 inch of cement and a }-inch marble slab. 
On the north side to carry the clock box there is a heavy table 3 feet 
9 inches square. The Observatory stands on somewhat elevated ground 
formed of basaltic traps, with their inter-trappean beds of hard red earth. 
The records commence on September 8, 1898. The period of the boom 
has been kept at 18 secs., the sensibility being such that a deflection of 
1 mm. corresponds to a,tilt of 0°38”. No ditticulties have been experi- 
enced in the working of the instrument beyond an occasional slight falling 
of the boom, due, perhaps, to a stretching of the silk thread at the upper 
end of the tie. The sensibility is determined weekly by observation and 
by deflections whilst the film is in the box, thus preserving a photographic 
record of the same. By stretching a fine wire across the slit in the clock 
box an accurate zero line is obtained. 
. Regular tremors and pulsations are absolutely absent. 
The list on the next page only contains records which correspond with 
records obtained in the Isle of Wight. The complete Bombay Catalogue, 
commencing on September 8, 1898, to June 2, 1899, contains 2,021 entries. 
These refer to shocks which were lccal, and do not appear to have reached 
Europe, curious irregular sinuosities varying in period from a few minutes 
to an hour, sudden displacements or dislocations in the position of the 
boom, and numerous thickenings of the normal record. The latter, in 
some instances, may be the result of slight earth tremors, but where they 
are continuous over several hours and have an irregular, bead-like 
appearance, it is likely that they are due to air currents. Movements 
due to such causes are most frequent at night. The cause of the sinuosi- 
ties and sudden displacements is at present unknown. 
In an official report on the condition and proceedings of the Colaba 
Observatory, dated April 29, 1899, in reference to Seismology, Mr. Moos 
says, that the seismograph appears to give every satisfaction. At first 
tremors were absolutely absent, but they appeared in the middle of 
November, and subsequently caused great trouble. To arrive at the 
causes producing these tremors, Mr. Moos has instituted a series of experi- 
