due to the enormous increase of the mortality among mere infants under one year of age ; and this increase is due not only to deaths at one age, but to deaths from one class of diseases, viz., bowel complaints. If the deaths from bowel complaints be deducted from the deaths from all causes, there remains an excess of deaths in the cold months, and a deficiency in the warm months. In other words, the curve of mortality is regulated by the large number of deaths from diseases of the respiratory organs. The curve of mortality for London, if mere infants be excepted, has thus an inverse relation to the temperature, rising as the temperature falls, and falling as the temperature rises. On the other hand, in Victoria, Australia, where the summers are hotter and the winters milder, the curves of mortality and temperature are directly related to each other mortality and temperature rising and falling together ; the reason being that in Victoria deaths from bowel complaints are much greater, and those from diseases of the respiratory organs much less than in London.
The curves show that the maximum annual mortality from the different diseases groups around certain specific conditions of temperature and moisture combined. Thus, cold and moist weather is accompanied with a high death-rate from rheumatism, heart diseases, diphtheria, and measles ; cold weather, with a high death-rate from bronchitis, pneumonia, &c. ; cold and dry weather, with a high death-rate from brain diseases, whooping-cough, convulsions; warm and dry weather, with a high death-rate from suicide and small-pox ; hot weather, with a high death-rate from bowel complaints ; and warm moist weather with a high death-rate from scarlet and typhoid fevers. (See Climate.) (A. B.)
ATMOSPHERIC RAILWAY, a railway in which the
pressure of air is used directly or indirectly to propel carriages,
as a substitute for steam. It was devised at a time
when the principles of propulsion were not so well under
stood as they are now, and when the dangers and inconveniences
attendant on the use of locomotives were very much
exaggerated. It had been long known that small objects
could be propelled for great distances through tubes by air
pressure, but a Mr Vallance, of Brighton, seems to have been
the first to propose the application of this system to passenger
traffic. He projected (about 1825) an atmospheric railway,
consisting of a wooden tube about 6 feet 6 inches in diameter,
with a carriage running inside it. A diaphragm fitting the
tube, approximately air-tight, was attached to the carriage,
and the air exhausted from the front of it by a stationary
engine, so that the atmospheric pressure behind drove the
carriage forward. Later inventors, commencing with Henry
Pinkus (1835), for the most part kept the carriages
altogether outside the tube, and connected them by a bar
with a piston working inside it, this piston being moved
by atmospheric pressure in the way just mentioned. The
tube was generally provided with a slot upon its upper
side, closed by a continuous valve or its equivalent, and
arrangements were made by which this valve should be
opened to allow the passage of the driving bar without
permitting great leakage of air. About 1840, Messrs
Clegg & Samuda made various experiments with an
atmospheric tube constructed on this principle upon a
portion of the West London Railway, near Wormwood
Scrubs. The apparent success of these induced the Dublin
and Kingstown Railway to adopt Clegg & Samuda’s scheme
upon an extension of their line from Kingstown to Dalkey,
where it was in operation in 1844. Later on, the same
system was adopted on a part of the South Devon line and
in several other places, and during the years 1844–1846
the English and French patent records show a very large
number of more or less practicable and ingenious schemes
for the tubes, valves, and driving gear of atmospheric
railways. The atmospheric system was nowhere permanently
successful, but in all cases was eventually
superseded by locomotives, the last atmospheric line being
probably that at St Germains, which was worked until
1862. Apart from difficulties in connection with the
working of the valve, the maintenance of the vacuum, &c.,
other great practical difficulties, which had not been
indicated by the experiments, soon made themselves known
in the working of the lines. Above all, it was found that
stationary engines, whether hauling a rope or exhausting a
tube, could never work a railway with anything like the
economy or the convenience of locomotives, a point which
is now regarded as settled by engineers, but which was not
so thoroughly understood thirty years ago. Lately, the
principle of the atmospheric railway has been applied on a
very large scale in London and elsewhere, under the name
of “Pneumatic Despatch” (q.v.), to the transmission of
small parcels in connection with postal and telegraph work,
for which purpose it has proved admirably adapted. (See
paper by Prof. Sternberg of Carlsruhe in Hensinger von
Waldegg s Handbuch für specielle Eisenbahntechnik, vol. i.
pt. 2, cap. xvii.
ATOM
ATOM (ἄτομος) is a body which cannot be cut in two. The atomic theory is a theory of the constitution of bodies, which asserts that they are made up of atoms. The opposite theory is that of the homogeneity and continuity of bodies, and asserts, at least in the case of bodies having no apparent organisation, such, for instance, as water, that as we can divide a drop of water into two parts which are each of them drops of water, so we have reason to believe that these smaller drops can be divided again, and the theory goes on to assert that there is nothing in the nature of things to hinder this process of division from being repeated over and over again, times without end. This is the doctrine of the infinite divisibility of bodies, and it is in direct contradiction with the theory of atoms.
The atomists assert that after a certain number of such divisions the parts would be no longer divisible, because each of them would be an atom. The advocates of the continuity of matter assert that the smallest conceivable body has parts, and that whatever has parts may be divided.
In ancient times Democritus was the founder of the atomic theory, while Anaxagoras propounded that of continuity, under the name of the doctrine of homœomeria (Ὁμοιομέρια), or of the similarity of the parts of a body to the whole. The arguments of the atomists, and their replies to the objections of Anaxagoras, are to be found in Lucretius.
In modern times the study of nature has brought to light many properties of bodies which appear to depend on the magnitude and motions of their ultimate constituents, and the question of the existence of atoms has once more become conspicuous among scientific inquiries.
We shall begin by stating the opposing doctrines of atoms and of continuity before giving an outline of the state of
