402 ; 
hundred times that attending the same amount of expansion by 
mechanical stress ; and, apart from the fact that with nickel and 
carbon the effects of change of temperature and of longitudinal 
stress are of an opposite nature, it is evident that the former are 
to be attributed to other causes than mere expansion. 
Compression was proved to produce on the electrical resistance 
of carbon a contrary effect to that caused by extension ; this 
statement applies to the alteration of specific resistance as well 
as of the total resistance. 
Stress, applied in a direction transverse to that cf the current, 
was also found to produce in several metals both temporary and 
permanent alterations of resistance of a nature opposite to those 
resulting from longitudinal traction. 
Stress applied equally in all directions by means of an 
hydraulic press was proved to diminish the resistance of copper 
and iron; and the experiments showed that the lowering of the 
temperature of the freezing-point of water can be accurately and 
readily measured by observations of the change of electrical 
resistance of a wire. 
The total resistance of most metals is permanently increased 
by permanent longitudinal extension, but with nickel the éo¢a/ 
resistance is permanently decreased, provided the extension does 
not exceed a certain limit: beyond this limit further extension 
causes the resistance to increa:e. 
The small effects which can be produced by permanent exten- 
sion, hammering, and torsion on specific electrical resistance 
were very fully investigated, and are shown in the paper by a 
series of curves. All the metals examined, except iron and 
nickel, have their specific resistances increased by strain caused 
by the above-mentioned processes, provided the strain does not 
exceed a certain limit, beyond this limit further strain decreases 
the specific resistance. In the case of iron and nickel, on the 
contrary, the specific resistance is at first decreased and afterwards 
increa ed. 
The effect on the resistance of annea’ed steel produced by 
heating and suddenly cooling was also studied, and it was proved 
that if the steel be heated to a temperature under ‘‘dull red,” 
sudden cooling decreases the resistance ; whereas if the metal be 
heated up to or beyond ‘‘du!l red,” sudden cooling zacreases the 
resistance: the strain, therefore, caused by this process, and that 
resulting from purely mechanical treatment, are similar as 
regards their influence on the electrical resistance, 
The amount of recovery of electrical corductivity produced 
by time in wires, which are in a state of strain, is shown in the 
paper for several metals by a series of curves, end these exhibit 
most conclusively the superiority of platinum-silver over German- 
silver when an accurate copy of a standard resistance has to be 
kept for a long period of time; in fact, of a'l the metals tested, 
German-silver showed the most marked recovery of conductivity, 
and platinum-silver the least. 
the recovery of electrical conductivity is in all cases attended 
with recovery of longitudinal elasticity and of tor-ional rigidity, 
A full examination of the influence of permanent strain on 
the susceptibility to temporary change of resistance from change 
of temperature showed that metals may be divided into two 
classes. In the first of these classes, which includes iron, zinc, 
and platinum-silver, the strained wire is ost increased in resist- 
ance by rise of temperature up to a certain limit of strain, whilst 
beyond this limit further strain diminishes the first effect. In 
the second class, which comprises copper, silver, platinum, and 
German-silver, the strained wire is /east increased in resistance 
by rise of temperature, but that, here again, after a certain 
point of strain has been reached, the first effect begins to be 
dimirashed, 2 
After some trouble, means were found of measuring with con- 
siderable accuracy at 100° C, the alteration of electrical resistance 
due to temporary longitudinal traction, and the experiments led 
to the belief that the elasticity of iron and steel is not tempo- 
rarily but fermanent/y increased by raising the temperature to 
100° C, Subsequently direct observations of the elasticity made 
in the manner described in Part I., but on shorter lengths of 
wire, placed in an air-chamber, the temperature of which could 
be maintained constantly at 100° C., proved beyond a doubt that 
if M. Wertheim, to whom we owe so much of our knowledge 
concerning elasticity, had examined the elasticity of iron and 
steel after these metals, tested at the higher temperature of 100° 
C., had again cooled down to the lower one, he would have found 
that what to him affeared, in the case of these metals (Ann. de 
Chimie et de Phys., 3me série, 1844, p. 431) to be a temporary 
increase of elasticity was really a permanent one, and if the 
NATURE 
[ Fed. 23, 1882 
wires used had been tested several times, first at the higher and 
then at the lower temperature, he would have also found, pro- 
vided sufficient rest after cooling had been allowed, that the elas- 
ticity of both iron and steel is éemforarily diminished by raising 
the temperature to 100° C, 
The temporary alteration of susceptibility to change of resist- 
ance from change of stress, which is etfected in the case of 
nickel by raising the temperature to 100° C., is as remarkable as 
the susceptibility itself, and the maximum diminution of resist- 
ance which could be produced by stress when the metal was at 
the temperature of the room was actually more than twice that at 
100° C, 
The alteration of electrical conductivity which can be pro- 
duced by magnetisation was carefully studied, and a full account 
of the modes of experimenting, of the apparatus employed, and 
the precautions adopted will be found in the paper. ‘The sub- 
stances examined were iron, steel, nickel, cobalt, bismuth, 
copper, and zinc, and in all cases, except that of copper, it was 
proved that longitudinal magnetisation increases the electrical 
resistance, whether the substance isin an annealed or unannealed 
condition. 
Of all the metals examined, annealed nickel was by far the 
most affected by a given amount of magnetising force. 
The increase of resistance produced by magnetisation can be 
very accurately represented by the formula y=a.a+é. 8B; 
where ¥ is the increase of re-istance, a the magnetising force, 8 
the induced magnetism, and a, 4 constants for the same sub- 
stance when the same amount of current per urit of area flows 
through the substance. 
In the paper, curves are shown exhibiting the connections 
between increase of re-istance, magnetisation, and induced 
magnetism, From these curves, and from the fact of the above- 
mentioned formula holding good, it is assumed that the resist- 
ance will go on increasing with the magnetising force even when 
the latter is so great that further increase of force does not 
produce perceptible increase of magnetism. 
The “circular” magnetisation which any magnetic substance 
undergoes when a current is conducted through it, seems to have 
very little or no apprecial le effect on the electrical resistance of 
the substance, so that, if we compare the resistances of iron and 
platinum, the ratio of the two will be independent of the eleciro- 
motor employed in the “ bridge.” 
The effects of temporary stress on the alteration by magnetism 
of the resistance of an iron or nickel wire are of a somewhat 
similar nature to those caused by the stress on the magnetic 
inductive capacity of these metals, and the same may be 
said with regard to the effects of the permanent strains due to 
extension, torsion, &c. Longitudinal stress which may be made 
to diminish considerally the susceptibility to alteration of re- 
sistance from magnetisation, cannot even when carried to the 
extent of causing breakage, change the ma¢ure of the alteration. 
There is apparently a close relationship between the ‘‘ vis- 
cosity” of a metal and its specific electrical resistance, and it 
seems very probable that a full investigation of the former of 
these two physical properties by the method of torsional vibra- 
tions would afford valuable information respecting the latter. 
Zoological Society, February 7.—Prof. W. H. Flower, 
F.R.S., president, in the chair.—Mr. Henry Seebohm, F.Z.S., 
exhibited and made remarks on a series of Goldfinches (ob- 
tained at Krasnoyarsk in Central Asia) which presented every 
form of transition between Carduelis major and Carduelis cant- 
ceps.—The Secretary exhibited, on behalf of Mr. Peter Inch- 
bald, F.Z.S., two curious hybrid ducks, obtained on some orna- 
mental water near Darlington.—Mr. St. George Mivart read a 
paper on the classification and distribution of the /urotda. 
He regarded this suborder as best divisible into three families— 
(1) Felidae, (2) Viverride, (3) Hyenide. The Felide he pro- 
posed to subdivide into but two genera, Felis and Cynelurus, 
the Viverride into the five subfamilies, (1) Viverrine, (2) Galt- 
dictina, (3) Euplerina, (4) Cryptoproctine, and (5) /erpestine. 
The Ayenide were referred to two subfamilies—(1) Proteline, 
(2) Hyontne, The author regarded Cryffoprocta as a true 
Viverrine animal, attaching but very little importance to dental 
characters save as discriminating species and genera. The Ga/i- 
dictine were arranged to include the genera Galidictis, Galidia, 
and Hemigalidia, the last-named genus haying been instituted 
for the species previously known as Galidia olivacea and Galiaia 
concolor, —Mr, W. A. Forbes read a paper on some points in 
the anatomy of the Indian Darter (lotus melanogaster), and 
gave a description of the mechanism of the neck in this genus 
