——————e 
TRANSACTIONS OF. SECTION A. 65 
or 
They may conveniently be discussed under five heads: 
(a) Diurnal waves, 
(6) Rapid changes in the vertical. 
(c) Gradual changes in the vertical. 
(d) Air tremors, 
(e) Earthquake shocks. 
At Mauritius, the diurnal waves are of greater amplitude than at any other 
observing station, with a well marked bi-diurnal effect, as shown by Bessel’s inter- 
polation formula, which, for the months of October 1898 to March 1899, is 
2°61 sin (9 + 295°-47’) + 0-73 + sin (20 + 3317-57’) + 0-30 sin (30+ 272°°57'), 
indicating a possible connection with the barometric pressure, the formula for the 
diurnal variation of which is 
0in-0108 ‘sin (9 + 49°32”) + 0in‘0285: sin (26 + 163° 2’) + 0in:0020° sin (3 + 26° 4’). 
In connection with the diurnal waves and gradual changes in the vertical it is 
very desirable that observations should be made with the boom lying east and 
west as well as north and south, and also with instruments in different localities 
and under varying conditions, 
Rapid changes in the vertical have occasionally occurred on a large scale, 
notably on December 5, 6, and 7, 1898, and J anuary 7, February 10 and 11, 1899. 
On December 5 the boom went out of range at 12h. 17m., after an easterly move- 
ment of 7’°5 in 10 minutes, due to very heavy rain at and to the west of the 
Observatory. On the other days the movements were nearly as large. 
A gradual change in the vertical has been going on since September last, the 
top of the boom pillar moving systematically towards the west. The gradual 
change in the sensibility of the instrument also indicates a north and south change 
in the vertical. 
Air tremors occur every night in spite of every precaution to insure copious 
ventilation, and to guard against convection currents. They begin at sunset with 
- small movements which rapidly become larger, but, though of varying amplitude 
during the night, do not showa marked maximum. They finally die away at 
sunrise. 
As a general rule the tremors are greatest when the fall of temperature during 
the night is greatest, but this is not always the case. 
The earthquake effects have, on the whole, been disappointing, the amplitude 
of motion keing small in every case. This gives rise to the question whether it is 
possible for the ocean to act as a damper to earthquake shocks. Records from the 
proposed observatory at Honolulu may throw more light on this subject. 
5. Progress in Exploring the Air with Kites. By A. LAWRENCE Rortcu, 
S.B., A.M, Director of Blue Hill Meteorological Observatory, Massa- 
chusetts, U.S.A. 
Since the report presented at Bristol no radical changes in the kites or 
apparatus at Blue Hill have been made, nor have the heights been increased 
greatly. Thus, while the average of the highest points attained by the meteoro- 
graph in each of the thirty-five flights during 1898 was 7,350 feet above the sea, 
the average of the ten flights during the first four months of 1899 was 7,680 feet, 
and that of the five flights between February 23 and 28 was 10,280 feet. The 
maximum height in 1898, viz. 12,070 feet above sea-level on August 26, was ex- 
ceeded by 370 feet on February 28, 1899, The smaller increase of altitude than 
in previous years indicates that the extreme heights to which our kites can rise is 
being approached. The features of the Blue Hill practice that enable great heights 
to be reached are the use of cellular kites having curved surfaces, giving greater 
lift, with self-regulating bridles, limiting the wind-pressure on each kite, and the 
attachment of the kites at different points on the wire, whereby their pull is dis- 
