SEPTEMBER II, 1902] 
NATURE 
477 
The investigations have shown that electric conductivity in 
pure metals varies almost inversely as the absolute temperature 
down to mznus 200 degrees, but that this law is greatly affected 
by the presence of the most minute amount of impurity. Hence 
the results amount to a proof that electric resistance in pure 
metals is closely dependent upon the molecular or atomic motion 
which gives rise to temperature, and that the process by which 
the energy constituting what is called an electric current is 
dissipated essentially depends upon non-homogeneity of 
structure and upon the absolute temperature of the material. 
It might be inferred that at the zero of absolute tem- 
pera'ure resistance would vanish altogether, and all pure 
metals become perfect conductors of electricity. This conclu- 
sion, however, has been rendered very doubtful by subse- 
quent observations made at still lower temperatures, which 
appear to point to an ultimate finite resistance. Thus the tem- 
perature at which copper was assumed to have no resistance was 
minus 223 degrees, but that metal has been cooled to mzzzvs 
253 degrees without getting rid of all resistance. The reduc- 
tion in resistance of some of the metals at the boiling-point of 
hydrogen is very remarkable. Thus copperhasonly1 percent , 
gold and platinum 3 per cent.. and silver 4 per cent. of the 
resistance they possessed at zero C., but iron still retains 12 per 
cent. of its initial resistance. In the case of alloys and impure 
metals, cold brings about a much smaller decrease in resistivity, 
and in the case of carbon and insulators like gutta-percha, glass, 
ebonite, &c., their resistivity steadily increases. The enor- 
mous increase in resistance of bismuth when transversely mag- 
netised and cooled was also discovered in the course of these 
experiments. The study of dielectric constants at low tempera- 
tures has resulted in the discovery of some interesting facts. A 
fundamental deduction from Maxwell’s theory is that the square 
of the refractive index of a body should be the same number as 
its dielectric constant. So far, however, from this being the 
case generally, the exceptions are far more numerous than the 
coincidences. It has been shown in the case of many sub- 
stances, such as ice and glass, that an increase in the frequency 
of the alternating electromotive force results in-a reduction of 
the dielectric constant to a value more consistent with Max- 
well’s law. By experiments upon many substances it is 
shown that even a moderate increase of frequency brings 
the large dielectric constant to values quite near to that required 
by Maxwell’s law. It was thus shown that low temperature 
has the same effect as high frequency in annulling the abnormal 
dielectric values. The exact measurement of the dielectric con- 
stant of liquid oxygen as well as its magnetic permeability, 
combined with the optical determination of the refractive index, 
showed that liquid oxygen strictly obeys Maxwell’s electro-optic 
law even at very low electric frequencies. In magnetic work 
the result of greatest value is the proof that magnetic suscepti- 
bility varies inversely as the absolute temperature. This shows 
that the magnetisation of paramagnetic bodies isan affair of 
orientation of molecules, and it suggests that at the absolute 
zero all the feebly paramagnetic bodies will be strongly magnetic. 
The diamagnetism of bismuth was found to be increased at low 
temperatures. The magnetic moment of a steel magnet is 
temporarily increased by cooling in liquid air, but the increase 
seems to have reached a limit, because on further cooling to the 
temperature of liquid hydrogen hardly any further change was 
observed. The study of the thermo-electric relations of the metals | 
at low temperatures resulted in a great extension of the well- 
known Tait Thermo-Electric Diagram. Tait found that the 
thermo-electric power of the metals could be expressed by a linear 
function of the absolute temperature, but at the extreme range of 
temperature now under consideration this law was found not 
to hold generally ; and further, it appeared that many abrupt 
electric changes take place, which originate probably from 
specific molecular changes occurring in the metal. The 
thermo-electric neutral points of certain metals, such as 
lead and gold, which are located about or below the boiling- 
point of hydrogen, have been found to be a convenient means 
of defining specific temperatures in this exceptional part of 
the scale. 
The effect of cold upon the life of living organisms is a matter 
of great intrinsic interest, as well as of wide theoretical im- 
portance, Experiment indicates that moderately high tempera- 
tures are much more fatal, at least to the lower forms of life, 
than are exceedingly low ones. Prof. McKendrick froze for an 
hour at a temperature of 182° C. samples of meat, milk, &c., in 
NO. 1715, vor. 66] 
| unfulfilled renown.” 
sealed tubes ; when these were opened after being kept at blood 
heat for a few days, their contents were found to be quite putrid. 
More recently some more elaborate tests were carried out at the 
Jenner Institute of Preventive Medicine on a series of typical 
bacteria. These were exposed to the temperature of liquid air 
for twenty hours, but their vitality was not affected, their func- 
tional activities remained unimpaired, and the cultures which 
they yielded were normal in every respect. The same result 
was obtained when liquid hydrogen was substituted for air. A 
similar persistence of life in seeds has been demonstrated even 
at the lowest temperatures ; they were frozen for over a hundred 
hours in liquid air, at the instance of Messrs. Brown and 
Escombe, with no other result than to affect their protoplasm 
with a certain inertness, from which it recovered with warmth. 
Subsequently commercial samples of barley, pea, vegetable- 
marrow and mustard seeds were literally steeped for six hours 
in liquid hydrogen at the Royal Institution, yet when they were 
sown by Sir W. T. Thiselton-Dyer at Kew in the ordinary 
way, the proportion in which germination occurred was no less 
than in the other batches of the same seeds which had suffered 
no abnormal treatment. Bacteria are minute vegetable cells, 
the standard of measurement for which is the ‘‘ mikron.” . Yet 
it has been found possible to completely triturate these 
inicroscopic cells, when the operation is carried out at the 
temperature of liquid air, the cells then being frozen into hard, 
breakable masses. The typhoid organism has been treated in 
this way, and the cell plasma obtained for the purpose of study- 
ing its toxic and immunising properties. It would hardly have 
been anticipated that liquid air should find such immediate 
application in biological research. A research by Prof. 
Macfadyen, just concluded, has shown that many varieties of 
micro-organisms can be exposed to the temperature of liquid air: 
for a period of six months without any appreciable loss of 
vitality, although at such a temperature the ordinary chemical 
processes of the cell must cease. At such a temperature the 
cells cannot be said to be either alive or dead, in the ordinary 
acceptation of these words. It is a newand hitherto unobtained 
condition of living matter—a third state. A final instance of 
the application of the above methods may be given. Certain 
species of bacteria during the course of their vital processes are 
capable of emitting light. If, however, the cells be broken up 
at the temperature of liquid air, and the crushed contents 
brought to the ordinary temperature, the luminosity function is 
found to have disappeared. This points to the luminosity not 
being due to the action of a ferment—a ‘‘ Luciferase ’’—but as 
being essentially bound up with the vital processes of the cells, 
and dependent for its production on the intact organisation of 
the cell. These attempts to study by frigorific methods the 
physiology of the cell have already yielded valuable and en- 
couraging results, and it is to be hoped that this line of investi- 
gation will continue to be vigorously prosecuted at the Jenner 
Institute. 
And now, to conclude an address which must have sorely 
taxed your patience, I may remind you that I commenced by 
referring to the plaint of Elizabethan science, that cold was not 
a natural available product. In the course of a long struggle 
with nature, man, by the application of intelligent and steady 
industry, has acquired a control over this agency which enables 
him to produce it at will, and with almost any degree of in- 
tensity, short of a limit defined by the very nature of things. 
| But the success in working what appears, at first sight, to be a 
quarry of research that would soon suffer exhaustion, has only 
brought him to the threshold of new labyrinths, the entangle- 
ments of which frustrate, with a seemingly invulnerable com- 
plexity, the hopes of further progress. In a legitimate sense all 
genuine scientific workers feel that they are ‘‘the inheritors of 
The battlefields of science are the centres 
of a perpetual warfare, in which there is no hope of final victory, 
although partial conquest is ever triumphantly encouraging the 
continuance of the disciplined and strenuous attack on the seem- 
ingly impregnable fortress of Nature, To serve in the scientifi 
army, to have shown some initiative, and to be rewarded by the 
consciousness that in the eyes of his comrades he bears the ac- 
credited accolade of successful endeavour, is enough to satisfy 
the legitimate ambition of every earnest student of Nature. 
The real warranty that the march of progress in the future will 
be as glorious as in the past lies in the perpetual reinforcement 
of the scientific ranks by recruits animated by such a spirit, and 
proud to obtain such a reward, 
