+ A ARR 
ON SEISMOLOGICAL INVESTIGATIONS. 91 
II. Black Spots.—These vary in diameter from 1 mm. to 8mm. In 
the centres of some of these there is a small white or brownish spot. 
As pointed out by Mr. W. H. Bullock of Newport, these closely resemble 
the spots produced when a piece of bromide paper is placed between the 
poles of. an induction coil. Sometimes they were very numerous, and at 
other times only one, perhaps, was found on a sheet. 
III. Singeings.—These occur on the lower edge of the paper where the 
brass cylinder joins the aluminium ring. They are sometimes continuous, 
or they may occur at intervals of half-an-hour to several hours on the length 
of a whole sheet. At other times only a group of two or three can be 
found during the entire week. 
If we attach the secondary terminals of an induction coil, one to the 
zine sheet and the other to the drum, bands, spots, and singeings closely 
simulating those recorded in the chalk pit may be obtained. 
Between August 19, 1906, and January 29, 1907, sixty-three jarge 
and small earthquakes were recorded at Shide. Out of these only ten 
nearly coincided with the time of occurrence of spots upon the paper. 
As at times the spots were so very numerous, we can only regard these 
coincidences as accidental. So far as we can see, bands, singeings, and 
spots occur in any state of the weather, and are therefore not connected 
with any ordinary meteorological conditions. 
Neither is there any distinct evidence that the markings are due 
to radio-activity. There appears, however, to be a suggestion that the 
luminosity occasionally seen at Pan Pit may result from a very feeble 
brush or glow-like electrical discharge. If this be so, it would also 
account for the bands on the photographic paper, the other markings being 
due to minute sparks. 
If we assume that there are radio-active or electrical emanations of 
hypogenic origin from our earth, it is difficult to escape from the conclu- 
sion that such must have an effect on what we call ‘climate,’ and hence 
upon everything which lives upon the surface of the globe. 
VI. Earthquakes and Changes in Latitude. By Professor C. G. Knott. 
In the last report Professor Milne continued his interesting com- 
parison of the occurrence of large earthquakes and the movements of the 
earth’s pole. The table he gave seems to call for a further discussion. 
Milne’s idea is to connect the occurrence of the earthquakes with the 
curvature of the path traced by the projection of the pole on the celestial 
sphere. But if there is to be any connection of the kind looked for, ought 
we not rather to consider the deviations from the mean value of the cur- 
vature or deflection (to use Milne’s terminology) than the deflections 
themselves ? For this mean curvature per tenth year we may consider 
to be due to some steadily acting dynamical cause, such as a slight de- 
parture from coincidence of the axis of rotation with the principal axis of 
inertia. From this point of view we should regard small deflections of 
5° or 10° as being abnormal equally with large deflections of 60° or 70°. 
Hence the earthquake frequency should be compared with the deviations 
of the deflections from the mean, which for the whole set of observations 
is almost exactly 30°5. I shall take the two groups as given in the last 
report together. By subtracting the mean deflection from the average 
deflection in each range we obtain what I shall call deviations from mean 
curvature. These form the first and fourth columns in the following 
