TRANSACTIONS OF SECTION A. 405 
2 Spr 
e = (na°ey) ee 
when V is the velocity of wave-propagation= -—. This is very small indeed 
ZI 
V Ky 
unless the period 7' be excessively small. 
6. Ona Method of producing Electro-magnetic Disturbances of comparatively 
Short Wave-lengths. By Professor Firzcerap, F.B.S. 
This is by utilising the alternating currents produced when an accumulator is 
discharged through a small resistance. It would be possible to produce waves of 
as little as 10 metres wave-length, or even less. 
7. Gyrostatic Determination of the North and South Line, and the Latitude of 
any place. By Sir Witi1AmM Tuomson, F.B.S. 
8. On a Model illustrating Helicoidal Asymmetry, and particularly the 
formation of Right- and Left-handed Helicoidal Crystals from a non- 
Helicoidal Solution. By Sir Witu1am THomsoy, F.R.S. 
9. Report of the Committee for the Harmonic Analysis of Tidal 
Observations.—See Reports, p. 49. 
10. On the Attractive Influence of the Sun and Moon causing Tides, and the 
Variations in Atmospheric Pressure and Rainfall causing Oscillations in 
the Underground Water in Porous Strata. By Isaac Roserts, F.G.S., 
PUA. 
The investigations haye been made at Maghull, which is an agricultural district 
about eight miles to the north-east of Liverpool, and relate to movements in the 
underzround water of the Triassic rocks, which lie beneath the surface of the 
ground. The water in these rocks is by capillarity made to form an inclined plane 
towards the sea, which at the point referred to has its surface at sixty feet above 
mean sea-level. The water-plane was shown to be in a state exceedingly sensitive 
to the following influences: namely, atmospheric pressure, lunar attraction, and 
solar attraction. 
In order to determine the relative extent of these and other disturbing in- 
fluences upon the water-plane, an artesian well was sunk in the Triassic rocks to 
a point below mean sea-level, and the rise and fall of the column of water sixty feet 
in height, freed from the friction in the rock, was used as the means of registering 
those disturbances in the water-plane, by using a mechanical contrivance of a float 
and drum, caused to revolve by clockwork, to trace a curve upon the diagram 
paper. 
The curve showed the extent from moment to moment of the atmospheric 
variations, and also the effects of the attraction of the sun and moon upon the 
water-plane in producing oscillations in the first case and true semi-diurnal lunar 
and solar tides in the latter case. 
The effect of the rainfall was also shown on the diagram. 
It was also shown that there were periods when all the forces which have been 
named were in equilibrium, the water-plane remaining in a state of perfect 
quiescence during those periods, 
11. On the Physical Theory of the Tides, with especial reference to their 
Diurnal Inequality. By the Rev. Jamus Pearson, M.A., F.R.A.S. 
The author commenced by explaining the great interest he had taken in the 
subject for twelve years past, and his confidence in the process which had attended his 
