7O 
NATORE 
[May 21, 1885 
of material ejected. The union of water with lavas may be 
compared with the solution of a gas in water; but there is 
reason to believe that in their deep-seated sources lavas contain 
little or no water. If igneous matter be extruded through dry 
strata the eruption might take place without explosive manifesta- 
tions. But if igneous matter be extruded through water-bearing 
beds, a kind of dialysis would take place between the igneous 
and aqueous masses. In this way the tension of the steam in 
the fluid rock may at last become so great that a fissure will be 
formed at the surface and volcanic action will follow. In this 
way the violence of a volcanic eruption will be determined by 
the quantity of water contained in the strata through which the 
lava passes in its passage to the surface, and by the temperature 
at which it reaches the surface. This theory explains the ac- 
knowledged sequence of volcanic outbursts of different degrees 
of violence, and the intervals which occur between them. It 
also explains the differences between the central and lateral 
eruptions of a great voleano and the phenomena attending its 
extinction. The structures of the igneous rocks, whether of 
basic or acid composition, are greatly modified by the presence 
in them of volatile ingredients. The succession of events indi- 
cated by the structure of Monte Somma and Vesuvius, Rocca- 
monfina, Monte Vulture, and Monte Nuovo show that after a 
long cessation of volcanic activity we have an extensive produc- 
tion of fragmentary and scoriaceous material, and that this is 
gradually succeeded by the eruption of lava-streams. The water 
and other volatile substances, such as sulphates and chlorides, 
which are given off abundantly in volcanic eruptions, may act 
as solvents for the various minerals which constitute lavas. 
aaa 
“Physical Scciety, May 9.—The meeting was held in the 
Physics Theatre of Clifton College, Bristol, in consequence of an 
invitation from the British Naturalists’ Society, Prof. Guthrie, 
President, in the chair.—Messrs. E. Cleminshaw, E, F. Herrom, 
and A. L. Selby were elected members of the Society.—The 
following communications were read :—On evaporation and dis- 
sociation, by Prof. W. Ramsay and Dr. S. Young. The authors 
gave the results of a series of investigations undertaken with the 
view of determining how far the passage of a liquid into a gas 
resembled the dissociation of a chemical compound. For this 
purpose the relation between the pressure and temperature of 
several dissociating substances such as ammonic carbonate, 
chloral hydrate, and phthalic acid had been examined. The 
authors hope shortly to publish the full details of these experi- 
ments and the conclusions arrived at.—On a model illustrating 
the propagation of the electro-magnetic wave, by Dr. S. P. 
Thompson. The model consists of two sets of beads. Each set 
is composed of a number of beads fixed to the extremities of 
wires, and by a suitable mechanical contrivance each executes an 
approximately harmonic motion at right angles to the wires and 
the mean plane of the set. The phase of each bead differing by 
a certain small amount from the succeeding, the whole represents 
a wave-propagation. The two sets are coloured differently and 
are so placed that their harmonic motions are executed at right 
angles about the same axis which represents the direction of 
propagation of an electro-magnetic disturbance, one wave being 
the electrostatic and the other the electro-magnetic displacement. 
—On aself-recording stress and strain indicator, by Prof. H. S. H. 
Shaw. This instrument was designed for one of Wicksteed’s 
50-ton single lever machines lately erected in the Engineering 
Laboratory of University College, Bristol, and has been found 
very simple and effective. In this testing machine the stress is 
applied by moving a mass of 1 ton along a lever ; this mass is 
connected by a cord with a vertical cylinder upon the indicator. 
This cylinder carries a paper wound around it, and turns upon 
its axis as the mass is moved towards the end of the lever. A 
pencil capable of a vertical motion bears against this, and thus 
horizontal distances upon the paper are measures of stress. The 
strain is measured by the vertical motion of the pencil, the posi- 
tion of which is controlled by a wire attached to the rim of a 
wheel above, upon the same axis of which are other smaller 
wheels, any one of which can be connected to a fine wire which 
is carried horizontally to the upper end of the test-piece passing 
over a pulley fixed to it, and is fixed to the lower end. Any 
extension of the test-piece can be multiplied at pleasure on the 
diagram by attaching the wire to a larger or smaller wheel.— 
Note on the so-called silent discharge of ozone generators, by 
Mr. W. A. Shenstone. Mr. Shenstone had arranged some 
apparatus by which this could be viewed. It seemed to have 
the characteristics of the Brush discharge. ; 
EDINBURGH 
Royal Society, April 20.—Robert Gray, Vice-President, in 
the chair.—In a paper on the effect of pressure on the tempera- — 
ture of minimum compressibility of water, Prof. Tait showed 
that the various results obtained admitted of easy deduction from 
theory.—A note on the variation by pressure of the melting- 
point of paraffin, &c., by Mr. W. Peddie; and a note on the 
thermal effects of tension in water, by Mr. G. N. Stewart, were 
submitted by Prof. Tait—Mr. Hugh R obert Mill read a paper 
on the temperature of the water inthe Firth of Forth, describing 
the work done at the Scottish Marine Station in this direction. 
The annual range of temperature, from summer maximum to 
winter minimum, was found to vary from nearly 40° F, at Alloa, 
where the river is fresh at low tide, to 20° at Queensferry, twenty 
miles seaward, and 10° at the mouth of the Firth thirty-five miles _ 
further on. The mean temperature of the water appeared to be — 
the same—47°"5—at all parts of the estuary, From June to — 
September the river was warmer than the sea, from October to — 
May it was colder, the average rise or fall in temperature at el 
f 
time along the Firth being 0°07 per mile. During the summer 
period the surface-water had a higher, and during winter a — 
lower, temperature than that beneath. The annual minimum — 
was reached in February, the maximum in August, and there 
were indications of the period being delayed toward the open 
sea. Materials are unfortunately wanting for discussing the 
variations of temperature in the North Sea beyond the influence 
of land. Mr. Mill showed curves of the monthly mean tem- 
peratures of the water plotted by the use of polar coordinates. 
Each month was represented by an angle of 30°; the tempera- 
ture being measured on the radius, equal values were shown as" 
concentric circles. Temperatures so plotted appear as closed 
curves, andin several cases those for the water resembled a circle 
placed eccentrically to the circles of reference. This method of 
curve-drawing has several advantages over that by the use of 
rectangular coordinates where periodic phenomena are to be 
represented.—Mr. J. T. Cunningham, of the Marine Station, read 
a paper on the relations of the yolk to the gastrula in teleosteans 
and in other types. 
Mathematical Society, May 8.—Mr. A. T. G. Barclay, 
President, in the chair.—Prof. Chrystal read papers on repeated 
differentiation, and on a process for finding the differential equa- 
tion of an algebraic curve. Dr. Thomas Muir made a com- 
munication on integration formule, and gave a historical note on 
the so-called Simson line.—Mr. J. S. Mackay contributed several 
mnemonics for certain mathematical constants. 
, SYDNEY 
Linnean Society of New South Wales, Feb. 25.—Prof. W. 
J. Stephens, M.A., F.G.S., President, in the chair.—The follow- 
ing papers were read:—On some reptiles from the Herbert 
River district, Queensland, by William Macleay, F.L.S., &c. 
Five new species are here described, Ainulza picta, and Tetra- 
dactylus guttulatus of the family Scincide, and of Ophidians 
Nardoa crassa, Tropidonotus ater, and Hoplocephalus assimilis. 
—Notes on certain Ceylonese Coleoptera, described by the late 
Francis Walker, by A. Sydney Olliff. In these notes Mr. Olliff, 
who had examined Mr. Walker’s types in the British Museum, 
endeavours to clear up the synonomy of the Clavicorn families. 
The name Asana was proposed for the 7rogosita rhyzophagoides 
of Walker, which cannot be referred to any known genus. In 
form it resembles Zzfasfis, but is characterised by the presenc 
of a scutellum.—On the flight of birds, by R. von Lendenfeld, 
Ph.D. 
PARIS 
Academy of Sciences, May 11.—M. Bouley, President, in 
the chair.—Remarks on the application of photography to the 
mapping of the stars by means of MM. P. and Pr. Henry’s 
new objectives, by M. Mouchez. The first essays with an ob- 
jective of 0°16 m. and a provisionary apparatus proved so suc- 
cessful, that a new instrument has been constructed with two 
objectives of 0°24 m. and 0°34 m. respectively. Although not 
yet completely regulated, this instrument has already yielded 
some remarkable results, fully justifying, if not exceeding, the 
hopes entertained by astronomers. It appears to have once for 
all solved the problem how to apply photography to the con- 
struction of a map of the heavenly bodies which shall include 
stars of the r4th and 15th magnitudes.—On the spontaneously 
reversible spectral rays, and on the analogy between the laws of 
