274 REPORTS ON THE STATE OF SCIENCE, ETC. 
of periods in each lunar day, has, from the first, given results strongly supporting the 
idea of lunar action. But the exact number of periods was at first wrongly assessed 
as 71, then as 70, and ultimately appears to be 68. In view of these successive 
changes, it is clearly desirable to obtain complete confirmation before publishing the 
details. It will easily be seen that each modification of the hypothesis in dealing 
with such a large mass of material has involved a good deal of work. 
Local Variations of the Earth’s Gravitational Field.—Report 
of Committee (Col. H. G. Lyons, Chairman ; Capt. H. Saw, Secretary ; 
Professor C. Vernon Boys, Dr. C. Cures, Col. Sir G. P. Lenox- 
ConyneHam, Dr. J. W. Evans, Mr. E. Lancaster JonES; the 
Drrector-GENERAL, Ordnance Survey; the Director, Geological 
Survey of Great Britain). 
Durine the year investigations have been conducted with the Eétvés Torsion Balance, 
both in the laboratory and in the field. Anew model of this instrument manufactured 
by a British firm has been tested, and compared with the instrument belonging to the 
Science Museum. These tests confirmed the superiority of the double beam instrument 
over the smaller type having only a single beam, and established the efficiency of the 
new instrument. 
A collapsible double-walled tent to protect the instrument during observations in 
the field has been designed and constructed in the workshops of the Science Museum. 
On completion of this, both the balances were tested in the open air near the laboratory. 
The readings were found to remain comparatively constant during the night, but were 
subject to considerable variations during the day, especially just after sunrise, and also 
at times when the temperature increased rapidly. An attempt to discriminate between 
the effects due to temperature fluctuations and solar radiation led to an investigation 
in the laboratory, in which the instruments were subjected to measured temperature 
changes in darkness. It was found that rapid fluctuations of temperature have a 
serious disturbing effect upon the stability of the balance beams. As an opportunity 
for a field test of the instruments occurred during the temperature tests, these latter 
were suspended, and will be continued in the near future. 
Field Tests.—At the request of the Shropshire Mines, Ltd., the two balances were 
transported by road to the Company’s mining areas near Shrewsbury. Observations 
were made with the British instrument at seven stations in a region below which a 
mineral lode was being worked at a depth of 400 ft. From the dip and direction of this 
lode it was expected to come near the surface somewhere in the area surveyed. The 
results of the seven observations showed that a mass of heavy mineral existed below 
the area. The position, extent, and depth of this deposit were roughly determined, and 
* is understood that steps are being taken by the Company to verify these conclusions 
y drilling. 
Both instruments were then moved to another area, well beyond the actual mine 
workings, and observations were made with the object of determining whether mineral 
lodes existed in this area. In this region observations were taken at twenty-three 
stations with a few repetitions, two stations being occupied each night. The computa- 
tion of these results is not yet completed, but there are indications of an anomaly near 
one of the stations. A full account of the work in this locality will be published in the 
near future. 
Both areas surveyed in this test were of a hilly character, hitherto considered un- 
suitable for the employment of the Hétvés Balance, owing to the difficulty of calcu- 
lating gravity effects of the topographical features. The terrain in each case was of a 
fairly uniform slope, extending well beyond the area surveyed, so that the effects due 
to this slope could be assumed to act along a certain direction, viz.: the line of 
greatest slope. The effects due to the suspected lodes, of which the general direction 
was indicated by geological data, were at right angles to the topographical effects, 
and the latter could therefore be ignored. 
This test is considered to be of importance, not merely as it verifies the suitability 
of the balance for general field work, but also because it demonstrates the utility of 
such a survey in a region characteristic of the mineral areas throughout Great Britain. 
In such areas, flat ground, free from topographical disturbing effects, can scarcely 
ever be expected. 
