7. 
Nov. 17, 1881] 
by the i ape and returns to its path, the line of least 
stance, through the molecules, whereas the stream of mole- 
sules at the higher exhaustion, carrying their clectricity 
with them, are carried away by the electric charge upon them, 
nd get utterly lost and scattered on striking the side of the tube, 
iding up a great deal of energy in the form of heat to the 
tube or to the glowing platinum or other substance in the tube. 
I must now show you the beautiful aurora tube which has 
een seen once in this theatre, and for which I am indebted to 
the kindness of Dr, De La Rue, It has been brought to the 
right state of exhaustion to show just those effects which will 
help better than any description of mine to give you an idea of 
the character of the aurora discharge in the middle regions of the 
atmosphere. 
By bringing a magnet to bear upon this discharge we may see 
the effect of terrestial magnetism on the aurora discharges in 
the atmosphere. 
Aurora Borealis, —Vhe aurora as seen in the north-eastern parts 
of Siberia, where it is often very brilliant, is described as con- 
sisting of single bright pillars rising in the north and in the 
north-east, gradually covering a Jarge space of the heavens ; 
these rush about fron place to place, and reaching up to the 
zenith, produce an appearance as if a vast tent was spread in the 
heavens, glittering with gold, rubies, and sapphires. 
More exact atte npts have been made to describe the aurora, 
aud perhaps I may be allowed to quote Dalton’s description of 
an aurora as seen by him, 
A remarkable red appearance of clouds was noticed in the | 
_ southern horizon, which afforded light enough to read by, and a | 
remarkable effect was expected, He says, ‘‘ There was a large 
luminous horizontal arch to the southward, and one or more 
concentric arches northward, All the arches seemed exactly 
bisected by the plane of the magnetic meridian. At 10.30 
streamers appeared in the S,. running to and fro from W, to 
Ii. ; they increased in number, and approached the zenith, when 
all of a sudden the whole hemisphere was covered with them, 
and exhibited such an appearance as baffles all description. The 
intensity of the light, the prodigious number and volatility of the 
beams, the grand intermiature of all the primitive colours in their 
utmost splendour, variegating the glowing canopy with the most 
luxuriant and enchanting scenery, afforded an awful, but at the 
same time a most pleasing and sublime spectacle. But,” he 
adds, ‘‘the uncommon grandeur of the scene only lasted one 
minute, The variety of colours disappeared, and the beams lost | 
their lateral motion, and were converted, as usual, into the 
flashing radiations ; but even then it surpassed all other appear- 
aices of the aurora, in that the whole hemisphere was covered 
with it.”” 
In his address before the British Association in 1863, Sir 
William Armstrong speaks of the sympathy between forces 
operating in the sun and magnetic forces on the earth, and 
notices a remarkable phenomenon seen by independent observers 
on September 1, 1859. ; 
‘© A sudden outburst of light, far exceeding the brightness of 
the sun’s surface, was seen to take place, and sweep like a 
drifting cloud over a portion of the solar sur'‘ace. ‘This was 
attended with magnetic disturbances of unusual intensity, and 
with exhibitions of aurora of extraordinary brilliancy. The 
identical instant at which the effusion of light was observed was 
recorded by an abrupt and strongly-marked deflection in the 
self-registering instruments at Kew. The magnetic storm com- 
menced before and continued after the event.” 
The daily and yearly periods of the magnetic changes, the 
change in the horizontal force depending on the sun’s rotation on 
his axis, the agreement of the eleven-year period of magnetic 
di turbances, sun-spots, and auroras, show that the sun plays a 
very important part in causing or governing both the regular and 
irregular magnetic changes, 
If the sun be assumed to bea very powerful magnet, then changes 
in his magnetism might be expected to affect the magnetism of the 
earth, although the effect could not be very large, unless the sun 
is magnetised to an intensity much greater even, compared to his 
mass, than the earth is magnetised. Then as there are tides in 
the sea around us and probably in the earth’s crust, so there are 
certainly very large tides in the ocean of air above us: and may 
not the sun and moon, by dragging this air towards them as the 
earth revolves, cause that friction between air and earth, and also 
that evaporation, which together may account for the presence of, 
and keep up the supply of, positive electricity in the air and 
negative electricity in the earth? Again, these tides in the 
atmosphere will cause the mass of it to lag behind the revolving 
NATURE 
| the management of the Society’s library. 
71 
solid earth, and at a height of thirty or forty miles we have a 
layer of air which, for air, is a comparatively good conductor of 
electricity. ere then we have not a lagging of the magnet 
behind the conductor, but a lagging of the conductor be- 
hind the magnet, and hence, according to the laws of Fara- 
day, we may expect a current or a, gradual heaping up of 
electricity in the air in the opposite direction to the current in 
the earth’s crust. Thus the regular tidal waves in the atmo- 
sphere would cause the gradual transfer of positive electricity 
from the poles towards the equator. ‘This transfer may be of 
the nature of a current of electricity or of a mass of air carrying 
a static charge of electricity with it, for as Prof. Rowland has 
shown that the motion of a static charge will produce magne- 
tism, 80 we may expect from the principles of conservation of 
electricity that a change in the position of a magnet will under 
such circumstances produce motion of the static charge of 
electricity. When the air becomes charged up to discharging 
point, then we may get the sudden discharges such as the aurora 
in the air and the earth current in the earth; and since the con- 
ducting layer of air approaches nearer to the earth in the colder 
polar regions, possibly within less than twenty miles of the earth's 
surface, it may be found that the discharge of the aurora may 
even take place from earth to air by gradual slow discharge, 
aided as it may be by the state of moisture of the air and by 
change of temperature and other causes. 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE 
CampriDGE.—W. H, Caldwell, B.A., of Caius College, has 
been nominated to study at the Zoological Station at Naples, 
Mr. F, M. Balfour, F.R.S., has been elected President of the 
Cambridge Philosophical Society. Prof. Newton in laying down 
the office referred with pleasure to the removal and the change in 
Since the transfer to 
the new room about 500 volumes have been presented to the 
library by Professors Humphry and Newton, Mr. J. W. Clark, 
Mr. F’. M. Balfour, and Mr, Horace Darwin. 
Open Scholarships for Natural Science have been offered by 
Trinity College (date of examination, March 22 next); subjects 
those of the Natural Science Tripos; by St. John’s College, 
subjects, Chemistry, Physic:, Physiology, with Geology, Com- 
parative Anatomy, and Botany (the last three only if notice be 
given beforehand), date, March 22; by Caius College, date 
| March 28, subjects, Chemistry, and either Biology or Physics ; 
| by Christ’s, Emmanuel, and Sidney Sussex Colleges, at a 
| common examination ; subjects, Physics, Chemistry, Biology, 
and Geology ; date March 28. 
University CoLLece, Liverroot.—The Council of the 
College have appointed Dr. W. A. Herdman to the protec up 
1 
| of natural history, founded by Lord Derby in connection wit 
University College. Dr. Herdman is a graduate of the Uni- 
versity of Edinburgh. He took the degree of Vachelor of 
Science in 1879 in the department of Natural Science, and in 
the same year was intrusted by Sir Wyville Thomson with the 
preparation of the report on the collection of Tunicula obtained 
during the Challenger Expedition. The Council have also ap- 
pointed Dr. J, Campbell Brown to the professorship of che- 
mistry in the same college. Dr. Campbell Brown has for 
several years held the office of borough and county analyst, and 
of lecturer upon chemistry at the Royal Infirmary School of 
Medicine. 
Dr. ALEXANDER BAIN, lately Professor of Iogicat Aberdeen, 
has been elected Lord Rector of that University. 
SOCIETIES AND ACADEMIES 
LONDON 
Anthropological Institute, November 8.—Prof. W, H. 
Flower, F.R.S., vice-president, in the chair.—The following 
new Members were announced :—Miss Becker, Mrs. R. Craw- 
shay, Mrs. Lloyd, Miss Mary Sheldon, Miss Eleanor E. Smith, 
Miss Wolfe, Prof. Acland, F.R.S., James Backhouse, William 
Bowman, F.R.S., Alfred T. Brett, M.D., Rev. H. Canham, 
John G. Garson, M.D., Hugh T, Hall, F.G.S., Capt. Hozier, 
W, J. Knowles, E. Llanfair Lewes, Alfred Lingard, M.B., G. D. 
Longstaff, M.D., William Parkin, H. Seebohm, F.L.S., Mark 
Stirrup, F.G.S., I. Stopes, F.G.S., Richard Thompson, Prof. 
E. Perceval Wright, F.L.S. ; also Dr. Josef Majer of Cracow 
as a Corresponding Member.—Dr, J. G, Garson exhibited some 
improved forms of anthropometric instruments.—Mr, Everard 
