102 REPORTS ON THE STATE OF SCIENCE.—1912. 
forming shell that contracts, which, by its sudden grip on the unshrinking 
nucleus, fractures itself.” 
XIV. Seismic and Volcanic Activity. 
From the ‘ Catalogue of Destructive Earthquakes ’ published in the 
British Association Reports for 1911 a list was constructed which gave 
the number of earthquakes which had occurred in the year 1800 and 
each following year up to 1900. A second list, based on information 
found in ‘ Die vulkanischen Erscheinungen der Erde,’ by Dr. Karl 
Schneider, gave the number of volcanic eruptions in each of these 
years. An inspection of these lists showed that from year to year 
seismic and volcanic activity seldom remained constant, but rose or 
fell. When all the entries in the ‘ Catalogue’ were considered it was 
seen that in forty-nine instances seismic and volcanic activity increased 
or decreased at the same time, but in the remaining fifty-one years 
one of these activities became greater whilst the other became less. If 
only the very large earthquakes having an intensity of II. or III. were 
considered, these numbers became respectively 52 and 47. 
Although we know that a megaseism may shake a dormant volcano 
into activity,® the figures here given suggest that volcanic and seismic 
activities of the world increase or decrease independently of each 
other. 
A stricter and therefore more satisfactory comparison of these 
activities may be obtained by reference to the chart which shows the 
chronologica! sequence of megaseisms between 1899 and 1910, together 
with the voleanic eruptions which have been recorded during the same 
period. The number of the latter, with fixed dates, was fifty-eight, 
and of the former 976. Eruptions and megaseisms have only occurred 
on the same day seventeen times. 
XV. On the Mitigation of Air Tremors at Cardiff. 
Mr. Thomas Chant writes me from Cardiff as follows :— 
‘The air tremors recorded by our seismograph, which have now 
been reduced, appear to have been caused by movements of the air 
within the covering case, set up by changes of temperature, and by 
currents of air moving in the room. 
‘In the first place it was thought that the heat from the small lamp 
changed the temperature in that part of the case near where it stands. 
To overcome this the lamp is now placed on two strips of asbestos 
fastened with seccotine to the movable top of the clock box, and two 
strips of asbestos have been fastened to the ends of the case (bridge). 
On these latter strips a piece of sheet tin has been fastened. Air now 
passes under the lamp and between the tin and the end of the bridge, 
thus preventing the case from becoming warm. 
‘ Secondly, movements of air within the case have been partially 
prevented in the following way: Pieces of thin mica have been fastened 
to the interior of the case across each end of the bridge, and the boom 
7 See ‘‘ Bedrock,’ No. 2, 1912. - 
§ See Brit. Assoc. Report, 1902, p. 72, and 1906, p. 97. 
