ON SEISMOLOGICAL INVESTIGATIONS. 87 
Coimbra (Observatorio Magnetico-Meteorologico), Portugal. 
Lat., 40° 12’ N.; long., 8° 25’ W., Green. ; alt., 141 metres. 
Foundation is on rock. The pier is a cut limestone, erected on a base of 
masonry, which rests on a 25 cm. layer of concrete, spread on the rock. 
Topographical Situation—On a hill-top. The height above the surrounding 
country is about 100 metres from the south side and 15 metres from the north. The 
slopes are gentle from all sides. 
Geological Structure—The nature of the rock is generally Old Red Sandstone. 
Depth of water-bearing strata undetermined. 
Time-heeping.—The time-keeping is secured by transits of stars, frequently 
observed in the adjoining Observatory. The watch of the seismograph is compared 
every day with a mean-time chronometer, whose corrections are carefully de- 
termined, i 
Dr. A. 8. VieGAs, Director. 
Edinburgh Royal Observatory, Edinburgh, Scotland. 
Lat., 55° 555 N.; long., 3° 11’ 3” W.; alt., 441 feet. 
Foundation is on granite pier, 3 feet high and 18 inches square, built on the 
surface of the rock, 431 feet above sea-level. A brass plate is placed under each of 
the levelling screws. : 
Topographical Situation—The Observatory, in the basement of which the instru- 
ment is placed, is situated on the ridge of the Blackford Hill, sloping upwards to 
the west, 1 in 10, to a height of about 520 feet above sea-level, and downwards to- 
wards the east, about 1 in 12, to the 300 feet contour line. Towards the north the hill 
slopes downwards, at first 1 in 7, afterwards less steeply, to about the 200 feet contour 
line, where it reaches the general level of the neighbourhood. Towards the south 
the decline is less rapid, being practically level for some 300 yards, after which it 
slopes to the top of a cliff, about 80 to 100 feet high, overhanging the Braid Burn. 
Geological Structure.—‘ Blackford Hill is practically one great mass of andesite 
lava (of Devonian age). There is a very thin band of tuff, which is a few hundred 
feet below the surface of the rock upon which the Observatory stands, but it is only 
2 feet in thickness, and it is almost as compact as the lava above it and below. 
The chief disturbing factor, so far as the andesite lava is concerned, is the shattered 
condition of the rock, arising from the joints and divisional planes which traverse 
it in many directions, But deep within the hill I think that these are almost 
negligible.’ 
THoMAS HEATH. 
Helwan Observatory, Cairo, Egypt. (See also Abbasia.) 
Lat., 29° 51’ 34" N.; long., 31° 20’ 30’ E.; alt., 115 metres above sea. 
Foundation is on Eocene limestone rock. 
Topographical Situation—The Observatory is situated on a spur of the eastern 
desert plateau, which is cut up by numerous ‘ wadies,’ or dry valleys. The spur, 
which rises some 55 metres above the level of Helwan town, is about 80 metres in 
width, with a flat top and a valley on either side. 
Geological Structwre.—Horizontally bedded Eocene limestone, mostly of a rather 
chalky nature, in thick beds, with occasional siliceous and marly bands. Compara- 
tively little vertical jointing is seen in the rock, but the horizontal bedding-planes are 
well marked. Water-bearing beds do not occur higher than. 60 metres below the 
site. 
The station is an astronomical observatory. 
. B. H. WADE, Superintendent. 
Honolulu Magnetic Observatory (U.S. C. and G. Survey). 
Lat., 21° 19'-2 N.; long., 158° 03':8 W. ; alt., 45 feet. 
Foundation is on a concrete pier on solid coral limestone. 
Topographical Situation—The Observatory is located on the large, level coral 
