354 
NATURE 

1 
| Aug. 31, 1871 | 

tropics with a force which can be computed from the above 
‘formula. If v be the eastward velocity at any parallel, the 
increase of pressure per degree of latitude is ‘oorg v sin A 
inches of mercury, and this accounts for the observed increase 
of pressure from the poles to the tropics, which is roughly ‘or 
inch per degree. 
If any stratum of air have less than the average eastward or 
westward velocity which prevails through the strata above it, it 
will not be able to resist the differential pressure from or towards 
the equator which their motion produces. For this reason the 
lowest stratum of air having its velocity relative to the earth 
kept down by friction, generally moves from the tropical belts 
of high barometer to the regions of low barometer at the poles 
and equator. This is the origin of our S.W. winds and of the 
prevalent N. W. winds of the Southern Ocean. 
The tendency of a moving mass of air to swerve to its own 
right in the northern hemisphere explains Buys Ballot’s law that 
the wind instead of blowing at right angles to the isobaric lines 
usually makes an angle of 20° or 30° with them, keeping the 
region of lower barometer on its left. The rotation of cyclones 
is an example of this law, and the pressure which the spirally- 
flowing streams exert to their own right in virtue of the earth’s 
rotation is the main cause of the excessive central depression. 
The author referred to Prof. J. Thomson’s paper (B.A. reports, 
1857), to Mr. Ferrel’s papers, and to NATURE, July 20, 1871. 
Remarks on Aerial Currents, by Prof. Colding. 
On a Nutoscope for showing graphically the Curve of Precession 
and Nutation, by Prof. Ch. V. Zenger. 
In the case ofa rapidly revolving solid, two things may take place 
according as the mass of the solid body is or isnot uniformly dis- 
tributed round the axis. Inthe first case, theaxisof rotation steadily 
holds its position during the rotation, as in the case of the gyro- 
scope. If a shock acts on the one side, the axis will describe a 
cone and its apex a circle, but if the mass on the disc be une- 
qually distributed (which is practically done by fastening a small 
circular plate by an excentric hole to the axis) the motion becomes 
more complicated, and the apex of the axis has a precessional 
and nutational motion. This motion in the apparatus described 
is traced ona pizce of blackened paper by the apex. The greater 
the disturbing weight is takea, the greater is the nutational 
motion, s9 that when it is very large the apex describes a spiral. 
The apex of the instrument is kept in slight contact with the 
blackened paper by means of a micrometer screw. 
On a Case of Transparency, by G. Johnstone Stoney. It is 
known that a gas becomes opaque if rays are passed through it 
of the same wave-length as that of the light whichit gives forth 
itself when incandescent, and in the present communication the 
author proposed an explanation of this fact, and gave an account 
of some experiments he had made with regard to the motions of 
the molecules in chloro-chromic anhydride, the spectram of which 
contained about 120 lines due to one motion of the molecules. 
Prof. Stokes and Sir W. Thomson made some remarks on the 
paper, in the course of which it was mentioned that in order that 
a sound might be propagated toa great distance, it was not neces- 
sary that the disturbance need be strictly periodic; Sir W. 
Thomson also remarked that he believed the vibrations of a 
molecule of a gas would be found to more resemble the vibra- 
tions of an elastic plate than those of a string. 
Remarks on a new Dip Circle, by Dr. Joule. 
SECTION C. ‘ 
SoME relics of the Carboniferous and other Old Land-surfaces 
were described by Mr. Henry Woodward. Whilst admitting 
that during particular eras circumstances may have favoured the 
development of special groups of organisms, which, in conse- 
quence, flourished in greater abundance than the rest, the author 
deprecated the idea of the prevalence of peculiar conditions at 
any time since the adyent of organic life on the globe. He re- 
ferred to the fact of sedimentary deposits being formed at the 
bottom of the sea as positive evidence of the waste of neighbour- 
ing land surfaces, and he remarked that if conditionsin the sea were 
favourable to the development of abundance of animal life, those 
on the land were in all probability equally so. He referred first to 
the abundant evidence of land-surfaces in Quaternary and Tertiary 
times. Truly marine deposits (such as the chalk) testify to the 
presence of land by the fossil remains of Pterodactyles, Cheloniz, 
and other shore-dwelling reptiles, whilst the Wealden beds, the 
Purbeck limestone, and Oolitic plant-shales afford abundant 

proofs of Mesozoic lands. Even the marine Solenhofen lime-— 
stone yields swarms of insects, flying lizards, and a true bird, 
beside plant remains. In the Triassic periods the earliest traces 
of Mammals appear, while ripple-marked slabs of sandstones 
show bird-like tracks and Labyrinthodont footmarks, telling ot 
the denizens of the old sea-shores and lakes. 
The author then described the Coal-period with its stores of 
land-plants and Reptilia, both aquatic and terrestrial, its insects — 
and Mollusca. He controverted the arguments of Dr. T. Sterry 
Hunt as to the exceptional condition of the atmosphere of the 
Coal-period, and showed that the presence of animal life dis- 
proyed the existence of an atmosphere charged with carbonic acid 
gas, and that plants would not be benetited thereby as Dr. 
Hunt supposed. 
On Monday, August 7, a report Ox Sections of Fossil Corals 
was made by Mr. James Thomson, F.G.S. The structural 
characters and development of the Carboniferous corals (about 
170 in number) were briefly pointed out and illustrated by a 
number of beautiful photographic plates. He explained the 
method by which the sections were prepared, and described a 
new process whereby he transferred the photographs of the 
structure to copper plates, that faithfully represented the most 
delicate parts. 
Sir Richard Griffith, Bart., F.R.S., gave an interesting account 
of the Boulder Drift and the Esker Hills of Ireland. Pointing 
to his large geological map of the country, he gave a brief 
description of its physical features and general geological struc- 
ture. He then described the boulder drift as consisting of sandy 
clay containing numerous stones and boulders, and having a 
thickness in the eastern part of about 100 feet; and he regarded 
it as formed bya great torrent moving suddenly and depositing 
rapidly. He next adverted to those remarkable ranges of hill, 
which varied in height above the surface of the boulder dift 
from twenty to sixty feet, the ascent being usually about twenty 
degrees on the west side, but less steep on the east. These 
Esker Hills were very numerous in the central portion of the 
country. Their general direction was from west to east ; and 
one greit esker, which extended from the county of Galway to 
Westmeath was used as the post road from Dublin to Galway 
for a length of thirty miles. These were formed after the 
Boulder Drift, by a shallow sea acting upon it. Sir Richard 
next directed attention to the occurrence of large erratic blocks, 
totally unconnected with the gravel, which were found resting on 
the surface throughout the entire district, from Galway Bay in 
an eastern and south-eastern direction, passing over the summits of 
the Sliebhbloom Mountains, near Roscrea, and extending from 
thence through the King’s and Queen’s counties. These blocks 
were all angular, and being composed of a peculiar porphyritic 
granite situated to the north of Galway Bay, they had evidently 
been transported by a current from the north-west. 
In the discussion which followed the reading of this paper, Mr. 
Milne Home, alluding to the Esker drift, said that similar 
instances of ridges accumulated by the sea were to be found 
in Stirlingshire and Berwickshire, and one was now 
being formed in the Firth of Forth, which went by the name 
of the Whale’s Back, and which was about two miles and three 
quarters in length ; he also thought that the Chesil Bank pre- 
sented a very similar structure to that of the Eskers, which he 
regarded as submarine banks. Mr. Geikie regarded the origin 
of the Eskers as still a puzzle to him. Mr. Symes, of the 
Geological Survey of Ireland, described the Eskers in County 
Mayo, which ‘he had minutely examined, and the carved-out 
ridges of boulder clay in the neighbourhood of Clew Bay and 
West Port. He said that the Eskers were evidently of a newer 
creation, and of a different origin from the boulder clay ridges, 
or “‘drumlins” as they are called in Ireland. Mr. Kinahan 
pointed out on the geological map the general lie of the Eskers 
in the centre of Ireland, and suggested that they must be due 
to the meeting of two tidal waves in a glacial sea, which came 
respectively round the north and south coast. Meeting mid- 
way, as it were, in the channel, they were forced along what is 
now the low-lying central part of the country, and on again 
meeting a northern current in the valley of the Shannon, the 
Eskers were formed in a curve in a northerly direction, which 
would thus account for the general way in which these Eskers 
lie. Mr. Kinahan also said that in the low valley between Bal- 
lina and the mouth of the Shannon, there was a newer drift, the 
coast lines of which can be traced in numerous places in the 
counties of Mayo and Galway, and then southward to Cork. 
A very important paper On the Systematic Position of Siva- 
therium Giganteum was read by Dr, Murie, but it was, perhaps, 
