ON SEISMOLOGICAL INVESTIGATIONS. 89 
running was only a little over a half that of the instruments at Pan Chalk 
Pit and Camborne. 
In each case the drums turned once a week, in which interval they 
used one sheet of bromide paper. 
Amongst various control experiments which were made I may mention 
the following :— 
I. Two pieces of chalk, one of which had been soaked for several 
hours in water, were placed over a piece of rapid bromide paper. Between 
the paper and the chalk there was an air space of about one milli- 
metre. At the end of forty hours development showed that no etfect 
of any description had been produced. Lach piece of chalk had a surface 
of about four square inches. 
II. For two weeks the instrument from the Pan Chalk Pit was 
mounted in my observatory, where a plastered brick wall took the place 
of the natural chalk face. To approximate to the conditions in the pit, 
inside the covering case a bowl of water and a wet sponge were placed. 
The developed films did not show any trace of photographic action. 
The ideas of making these last experiments arose from communications 
with the manager of the Kodak works at Harrow, who pointed out that 
effects had been produced upon photographic surfaces inclosed in dark 
slides made from aluminium, and also in apparatus where movable parts 
of aluminium and zinc were used. The drums used at Shide and at 
Camborne were made of brass and aluminium, and they passed very 
closely to a fixed sheet of zinc. But I have only got photographic effects 
when the apparatus was underground in the places described. 
IIT. Several pieces of bromide paper have been inclosed in black 
envelopes and placed against the face of the chalk in the instrument 
chamber at the Pan Pit. After a week’s contact there was no trace of 
photographic action on the film when it had been developed. 
IV. Several pieces of bromide paper have been placed in envelopes 
which had a thin glass window which touched the chalk. After a week’s 
exposure the paper opposite the window was sometimes blackened. 
More Important Observations. 
eee 
Pan Chalk Pit. 
November 12 to 19, 1906.—12th, 14h. 
to 14th, 17h. 45m, strong singeings. At 
this time it was foggy and frosty. Inter- 
mittent singeings 30m. to 3h. apart. 
November 19 to 26.—1i9th, 10b., to 
21st, 10h., strong singeings. Weather 
frosty, finishing with rain. Up to 25th 
slight intermittent singeings. During 
this period there were many spots; one 
group agrees with a slight earthquake on 
21st at 23h. 57m. 
November 26 to December 3.—26th to 
28th, spots fairly numerous. Singeings 
strong November 26th, 16h., to 27th, 6h. 
Weather dull and fine. Spots also 
numerous December, 3h. to 20h., and 
singeings (strong). Slight rain and 
stormy. 
Camborne. 
November 13 to 19, 1906.—No record, 
as paper had been exposed to light; still 
on it three parallel lines can be traced, 
made up apparently of a series of spots 
bounded by a luminous band. 
November 19 to 24,—Parallel bands 
reproduced, but the dotted lines are 
broken. On 19th, 10h. to 20h., and 23rd, 
10h., singeings; 19th, strongly marked. 
November 24 to December 1.—Upper 
and lower luminous bands surrounding 
broken dotted line. 
December 1 to 8.—Luminous bands 
and broken lines continue. Strong 
singeings December 1, 16h. to 3rd, 
10h.; 4th, 10h. ; 8th, 10h. Weather foggy 
and stormy. 
