468 
philosophy that was so troublesome and full of hardships.” 
He looked upon his results but as a ‘* beginning ” in this field 
of inquiry, and for all the trouble and patience expended he 
consoled himself with the thought of ‘‘men being oftentimes 
obliged to suffer as much wet and cold and dive as deep to fetch 
up sponges as to fetch up pearls.” After the masterly essay of 
Boyle, the attention of investigators was chiefly directed to im- 
proving thermometrical instruments. The old air thermometer 
of Galileo being inconvenient to use, the introduction of fluid 
thermometers greatly aided the inquiry into the action of heat 
and cold. For a time great difficulty was encountered in select- 
ing proper fixed points on the scales of such instruments, and 
this stimulated men like Huygens, Newton, Hooke and 
Amontons to suggest remedies and toconduct experiments. By 
the beginning of the eighteenth century the freezing-point and 
the boiling-point of water were agreed upon as fixed points, 
and the only apparent difficulties to be overcome were 
the selection of the fluid, accurate calibration of the 
capillary tube of the thermometer, and a general un- 
derstanding as to scale divisions. It must be confessed 
that great confusion and inaccuracy in temperature observations 
arose from the variety and crudeness of the instruments. This 
led Amontons in 1702-3 to contribute two papers to the French 
Academy which reveal great originality in the handling of the 
subject, and which, strange to say, are not generally known. 
The first discourse deals with some new properties of the air 
and the means of accurately ascertaining the temperature in any 
climate. He regarded heat as due to a movement of the par- 
ticles of bodies, though he did not in any way specify the nature 
of the motion involved ; and as the general cause of all terrestrial 
motion, so that in its absence the earth would be without move- 
ment in its smallest parts. The new facts he records are obser- 
vations on the spring or pressure of air brought about by the 
action of heat. He shows that different masses of air measured 
at the same initial spring or pressure, when heated to the boil- 
ing-point of water, acquire equal increments of spring or pres- 
sure, provided the volume of the gas be kept at its initial value. 
Further, he proves that if the pressure of the gas before heating 
be doubled or tripled, then the additional spring or «pressure 
resulting from heating to the boiling-point of water is equally 
doubled or tripled. In other words, the ratio of the total spring 
of air at two definite and steady temperatures and at constant 
volume is a constant, independent of the mass or the initial 
pressure of the air in the thermometer. These results led to the 
increased perfection of the air thermometer as a standard instru- 
ment, Amontons’ idea being to express the temperature at any 
locality in fractions of the degree of heat of boiling water. The 
great novelty of the instrument is that temperature is defined 
by the measurement of the length of a column of mercury. In 
passing, he remarks that we do not know the extreme of heat and 
cold, but that he has given the results of experiments which 
establish correspondences for those who wish to consider the sub- 
ject. In the following year Amontons contributed to the 
Academy a further paper extending the scope of the inquiry. He 
there pointed out more explicitly that as the degrees of heat in 
his thermometer are registered by the height of a column of mer- 
cury, which the heat is able to sustain by the spring of the air, it 
follows that the extreme cold of the thermometer will be that 
which reduces the air to have no power of spring. This, he 
says, will be a much greater cold than what we call *‘ very cold,” 
because experiments have shown thatif the spring of the air at 
boiling-point is 73 inches, the degree of heat which remains in 
the air when brought to the freezing-point of water is still very 
great, for it can still maintain the spring of 514 inches. The 
greatest climatic cold on the scale of units adopted by Amontons 
is marked 50, and the greatest summer heat 58, the value for 
boiling water being 73, and the zero being 52 units below the 
freezing-point. Thus Amontons was the first to recognise that 
the use of air asa thermometric substance led to the inference 
of the existence of a zero of temperature, and his scale is nothing 
else than the absolute one we are now so familiar with. It re- 
sults from Amontons’ experiments that the air would have no 
spring left if it were cooled below the freezing-point of water to 
about 24 times the temperature range which separates the 
boiling-point and the freezing-point. In other words, if we 
adopt the usual centennial difference between these two points 
of temperature as 100 degrees, then the zero of Amontons’ 
air thermometer is mzzus 240 degrees. This is a remarkable 
approximation to our modern value for the same point of mznus 
273 degrees. It has to be confessed that Amontons’ valuable 
NO. 1715, VOL. 66] 
NATURE 
[SEPTEMBER II, 1902 
contributions to knowledge met with that fate which has so 
often for a time overtaken the work of too-advanced discoverers ; 
in other words, it was simply ignored, or in any case not appre- 
ciated by the scientific world either of that time or half a century 
later. It is not till Lambert, in his work on ‘‘ Pyrometrie” 
published in 1779, repeated Amontons’ experiments and endorsed 
his results that we find any further reference to the absolute 
scale or the zero of temperature. Lambert’s observations were 
made with the greatest care and refinement, and resulted in 
correcting the value of the zero of the air scale to minus 270 
degrees as compared with Amontons’ minus 240 degrees. 
Lambert points out that the degree of temperature which is 
equal to zero is what one may call absolute cold, and that at this 
temperature the volume of the air would be practically nothing. 
In other words, the particles of the air would fall together and 
touch each other and become dense like water ; and from this it 
may be inferred that the gaseous condition is caused by heat. 
Lambert says that Amontons’ discoveries had found few adherents 
because they were too beautiful and advanced for the time in 
which he lived. 
About this time a remarkable observation was made by 
Prof. Braun at Moscow, who, during the severe winter of 1759, 
succeeded in freezing mercury by the use of a mixture of 
snow and nitric acid. When we remember that mercury was 
regarded as quite a peculiar substance possessed of the essential 
quality of fluidity, we can easily understand the universal 
interest created by the experiment of Braun. This was 
accentuated by the observations he made on the temperature 
given by the mercury thermometer, which appeared to record 
a temperature as low as mznus 200° C. The experiments 
were soon repeated by Hutchins at Hudson’s Bay, who con- 
ducted his work with the aid of suggestions given him by 
Cavendish and Black. The result of the new observations was 
to show that the freezing-point of mercury is only crs 
4o° C., the errors in former experiments having been due to 
the great contraction of the mercury in the thermometer in 
passing into the solid state. From this it followed that the 
enormous natural and artificial colds which had generally 
been believed in had no proved existence. Still the possible 
existence of a zero of temperature very different from that 
deduced from gas thermometry had the support of such distin- 
guished names as those of Laplace and Lavoisier. In their 
great memoir on “ Heat,” after making what they consider 
reasonable hypotheses as to the relation between specific heat 
and total heat, they calculate values for the zero which range 
from 1500° to 3000° below melting ice. On the whole, they 
regard the absolute zero as being in any case 600° below the 
freezing-point. Lavoisier, in his ‘‘ Elements of Chemistry ” 
published in 1792, goes further in the direction of indefinitely 
lowering the zero of temperature when he says, ‘‘ We are still 
very far from being able to produce the degree of absolute cold, 
or total deprivation of heat, being unacquainted with any degree 
of coldness which we cannot suppose capable of still further 
augmentation ; hence it follows we are incapable of causing the 
ultimate particles of bodies to approach each other as near as 
possible, and thus these particles do not touch each other in any 
state hitherto known.” Even as late as the beginning of the 
nineteenth century we find Dalton, in his new system of 
“*Chemical Philosophy,” giving ten calculations of this value, 
and adopting finally as the natural zero of temperature mus 
3000° C. 
In Black’s lectures we find that he takes a very cautious view 
with regard to the zero of temperature, but as usual is admirably 
clear with regard to its exposition. Thus he says, ‘‘ We are 
ignorant of the lowest possible degree or beginning of heat. 
Some ingenious attempts have been made to estimate what it 
may be, but they have not proved satisfactory. Our knowledge 
of the degrees of heat may be compared to what we should 
have of a chain the two ends of which were hidden from 
us and the middle only exposed to our view. We might put 
distinct marks on some of the links, and number the rest 
according as they are nearest to or further removed from 
the principal links; but not knowing the distance of 
any links from the end of the chain we could not compare 
them together with respect to their distance, or say that one 
link was twice as far from the end of the chain as another.” It 
is interesting to observe, however, that Black was evidently 
well acquainted with the work of Amontons, and strongly sup- 
ports his inference as to the nature of air. Thus, in discussing 
the general cause of vaporisation, Black says that some philoso- 
