68 REPORTS ON THE STATE OF SCTENCE.—1915. 
The improvements it is proposed to incorporate are electro-magnetic 
damping, more delicate means of calibrating, clearer definition in the 
trace of seismograms, a still further economic use of the sensitised 
paper, increased maximum amplitude, adjustable light slits, &c. 
Hitherto these pendulums have been quite undamped (except for 
the natural damping of the mechanism), and herein has partly lain 
the secret of its very high degree of sensitivity. The fact has long 
been recognised that most forms of damping, such as the air and liquid 
systems used on the Continent, would be too crude to apply to so 
sensitive an apparatus. 
The Galitzin method of electro-magnetic damping seemed to offer 
the best opportunities for development; but the lightness and delicacy 
of the Milne booms is such that the addition of heavy copper plates 
was impracticable. Tests have been made with aluminium foil, and 
it has been found that this metal is superior to copper for the purpose, 
in so far that its conductivity is higher than that of copper, weight 
for weight. 
Partly due to the feeble inertia of these pendulums and partly to 
the efficiency of the aluminium as a damping medium, it is found that 
a strong magnetic field acting upon five grains of the metal will give 
a damping effect of 8:1. Any lower value is readily obtained by a 
sliding adjustment. 
The new calibrating device will obviate the usual disturbance of 
the apparatus in the process, either by opening cover cases or walking 
round the pedestal. The usual calibrating screw is fitted with a worm 
and wheel; one whole turn of the worm produces a 2-degree turn of 
calibrating screw, which gives a tilt of 2” of arc. 
The worm is operated from the vicinity of the clock-box by means 
of an intervening length of flexible cable, and the movement of the 
calibrating screw is read on a scale fixed on top of the recording case. 
The angular motion is read by means of a beam of light from a mirror 
fixed to the calibrating screw. This direct reading eliminates any error 
due to flexure in the cable or worm. 
XV. Indexing Materials published by the British Association and the 
Seismological Society of Japan relating to Geophysics. 
Although the British Association has since the year 1841 published 
fifty-three Annual Reports and other notices about seismology and other 
branches of geophysics, it is but rarely these are referred to by modern 
investigators. ‘To make these publications better known and to give 
to geophysicists an easy means of reference to them, the following 
index has been compiled. With these a few references are made to 
the ‘ Transactions of the Seismological Society of Japan’ and the 
‘Seismological Journal.’ The former are indicated by the letters 
T.S. and the latter by S.J. These for the most part are detailed 
accounts of investigations which in the Reports of the British Asso- 
ciation are only referred to as abstracts. 
Authors’ names are attached to all reports and writings, with the 
exception of those written by myself. 
