462 
NATURE 
circumstances no ship can be safe, how great soever her statical 
stability. All these principles have been known for some years 
through Mr. Froude’s researches. The lecturer exhibited a 
machine he had contrived for illustrating them, in which the 
dynamical conditions of vessels of different degrees of stiffness 
and steadiness were approximately imitated by means of a 
peculiarly-constructed pendulum hanging from a pin, whose mo- 
tions imitate those of a particle of water disturbed by wayes, 
SECTIONAL PROCEEDINGS 
SEcTION A.—MATHEMATICAL AND PHYSICAL SCIENCE 
On the Mode of Action of Lightning on Telegraphs, and 
on a New Method of Constructing Telegraph Coils.—My. S. 
Alfred Varley. He remarked that when lightning storms 
occur in the neighbourhood of telegraph wires, although the 
wires may not be actually struck, powerful currents are 
induced in them which may be sufficiently strong to fuse the 
coils, but which more frequently simply demagnetise, and as 
often reverse the magnetism of the magnetic needles situated in 
the coils of needle telegraph instruments. Thus, not only is a 
considerable amount of damage done annually to telegraph in- 
struments, but telegraphic communication is very liable to serious 
interruption. Mr. Varley mentioned a number of observations 
going to prove that an interval of dust separating two metallic 
conductors opposes practically a decreasing resistance to an 
increasing electrical tension, and that incandescent particles of 
carbon oppose about ;5th part of the resistance opposed by a 
needle telegraph coil. Reasoning upon these data, he has con- 
structed an instrument, the main feature of which is what he 
terms a “‘lightning bridge.” Two thick metal conductors, 
terminating im points, are inserted usually in a piece of wood. 
These points approach one another within about ;th of an inch 
in a chamber cut in the middle of the wood. This bridge 
is placed in the electric circuit in the most direct course 
which the lightning can take, and the space separating 
the two points is filled loosely with powder, which is placed 
in the chamber, and surrounds and covers the extremities of 
the pointed conductors. The powder employed consists of 
carbon (a conductor) and a non-conducting substance in a 
minute state of division. When this instrument is used, there- 
fore, lightning which strikes a circuit finds in its direct path not 
a space of air buta bridge of powder, consisting of particles of 
conducting matter in close proximity to one another. These the 
lightning connects under the influence of the discharge, and the 
particles are thrown into a highly incandescent state. The 
secondary current, developed by the demagnetisation, finds an 
easier passage across this heated matter than through the coils. 
These lightning bridges have been in use since January 1866, 
and at the present moment there are upwards of 1,000 doing 
duty in this country alone. Yet not a single case has occurred 
of a coil being fused when protected by them. The reason why 
a powder consisting entirely or chiefly of conducting matter 
cannot be safely employed is, that although it can oppese a 
practically infinite resistance to the passage of electricity of the 
tension of ordinary working currents, when a high tension dis- 
charge occurs, the particles under the influence of the discharge 
generally arrange themselves so closely as to make a conducting 
connection between the two points of the lightning bridge. In 
the course of his exposition, Mr. Varley endeayoured to prove 
that when telegraphic circuits protected by ordinary protectors 
are struck by lightning, it is to the secondary current and not to 
the main discharge that the fusion must be attributed. He also 
pointed out the defects of the protector, which consists of two 
silk wires wound side by side upon a bobbin. 
Mr. Varley also read a second paper containing 4 Description 
of the Electric Time Signal, at Port Elizabeth, Cape of Good 
Hoe. After an elaborate account of the Liverpool time ball, 
he proceeded to say that in the year 1859, Sir Thomas Maclear, 
the Astronomer Royal of the Cape of Good Hope, inspected the 
electrical time signals in this country, with a view to erecting 
time balls in connection with the Royal Observatory at -Cape 
Town. Sir T. Maclear remarked the greater rapidity of action 
of the Liverpool trigger, and this led to Mr. Varley’s afterwards 
designing and constructing at different times two triggers for use 
inthe Cape. Both these triggers discharged more rapidly than 
the Liverpool trigger. In Sepiember 1864, he was requested 
to construct a trigger for discharging a time ball to be erected at 
Port Elizcbeth, Ie considered the intervention of any relay or 
[ Océ. 6, 1870 
secondary apparatus to be objectionable. He therefore deter- 
mined if possible to construct the trigger sensitive enough to be 
discharged by the batteries in the Cape Town Observatory, and 
in its construction he adopted a modification of a principle first 
introduced by Professor Hughes in his printing telegraph (de- 
scribed at the Newcastle meeting). 
The trigger was constructed with a soft iron armature, ren- 
dered magnetic by induction from a compound bar magnet, 
and which strongly attracted the soft iron cores of an electro- 
magnet, but which was prevented from actually touching the 
poles of the electro-magnet. 
A spiral spring attached to this armature was so adjusted 
that it nearly overcame the magnetic attraction induced by the 
bar magnets. 
The timecurrent polarised the electro-magnet in the opposite 
direction to that.induced by the bar magnets, and as the attraction 
between the armature and the soft iron cores was already almost 
overcome by the spiral spring, a very small amount of polari- 
sation in the opposite direction was necessary to release the 
armature, which was rapidly pulled away by the spiral spring, 
and the trigger discharged. 
There were some other alterations made in the general mecha- 
nical construction of this trigger, but they may be regarded as 
matters of detail. 
The rapidity of discharge was very great, »>;th part of a 
second only elapsed between the arrival of the time current and 
the falling of the ball. 
From a report in the Port Elizabeth paper of August 29, 1865, 
giving an account of the inauguration of this time signal, and 
forwarded to Mr. Varley by Sir Thomas Maclear, it appears that 
the time elapsing between the time current leaving the Obser- 
vatory at Cape Town and the receipt at Cape Town of the signal 
announcing the falling of the ball, is only ~;th of a second. 
The time which elapsed between the Greenwich current 
reaching Londonand the falling of the ball at Liverpool was 
zoth of a second. In other words, the Algoa ball is discharged 
from a distance of 500 miles in less than }th of the time of that of 
the Liverpool ball. 
What is being daily done in the Cape can, however, be best 
summed up by a short quotation from a letter received from 
Sir Thomas Maclear, giving an account of the successful in- 
auguration of this time signal. After detailing the general 
arrangements, Sir Thomas Maclear goes on to state: ‘*A 
few tentative signals having proved satisfactory, the ‘ preface’ 
was issued from the Observatory at ten minutes before one 
o’clock, and at the instant of one o'clock, the Observatory 
time-ball clock closed the circuit discharging the Observatory 
ball, the Simon’s Town ball, twenty-four miles distant ; the 
Cape Town time gun, three miles distant ; and the Port Eliza- 
-beth ball, distant 500 miles,” 
On the present State of the Question relative to Lunar Activity 
or Quiescence.—W. R. Birt, F.R.A.S. From the time of 
Schroter, the question of change on the moon’s surface has been 
more or less agitated. The Se/enotopographische Fragmente con- 
tains numerous instances of what he considered to be changes of 
a temporary character, and a few of amore permanent nature, as 
the formation of new craters. It is, however, notorious that he 
failed to establish the fact of a decided change in any one in- 
stance; nor is this to be wondered at when we consider the 
paucity of the materials he had at his command. Notwithstand- 
ing the comparative neglect into which the observations recorded 
in the ‘‘ Fragments” have fallen, and the judgments passed upon 
them by some of the best known selenographers, there can be no 
question that they embody the results of zealous and persevering 
attention to the moon’s surface, and ought not to be passed over 
in the examination of any given spot, the history.of which we are 
desirous of becoming acquainted with during the earliest period of 
descriptive observational selenography. 
The labours of Schroter’s successors, Lohrmann, and Beer 
and Madler, have added greatly to the number of objects, either 
as delineated on their maps or referred to in their letter-press. 
Lohrmann appears to have carefully studied Schroter’s results, as 
we find him quoting the measures obtained by Schroter in several 
instances. On examining the results of the two greatest seleno- 
graphical works of the present century, and comparing the one 
with the other, we find precisely the same kind of phenomena 
presenting themselves which in a great measure perplexed 
Schroéter ; but as Lohrmann and Madler worked independently 
of each other, and Madler evidently had a very low idea of the 
value of the preceding labotfis of Schroter, these phenomena 
