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rapidity. Before the end of the century various treatises on 
pneumatics had appeared, and perhaps no science so speedily 
reached maturity. The above sciences, it will be noted, relate 
to the properties of matter in its three forms of solid, liquid, and 
gas, when at rest and in motion. We come next to certain 
sciences which treat of the more subtle and intimate motion of the 
particles or molecules of matter, with various velocities and in 
various directions. Beginning with Acoustics, we have the vibra- 
tory motion of particles across a position of rest resulting in the 
production of what we call sound. The science of sound, 
although more or less linked with the art of music, has existed 
as an experimental science for less than a century. Vibratory 
moyements of the same character taking place in a subtle kind 
of matter called the ether or interstellar medium, constitute Heat 
and Light, the difference being one of velocity, and thus of degree 
rather than of kind, Finally, we may assume that A/agnetism 
and Zéectricity are conditions of matter perhaps not differing 
much from those which constitute light and heat. 
The science of Zight is certainly one of the older of the 
sciences. Euclid endeayoured to explain the laws of vision ; 
Ptolemy, the astronomer, wrote a treatise on Light ; the reflec- 
tion of light by mirrors, and its refraction by lenses, were well 
known facts in the time of Archimedes. Various treatises on 
the subject appeared during the Middle Ages. The Ars Magna 
lucts et umbre of Athanasius Kircher, published in the seven- 
teenth century, is a great folio, full of plates. Not long after its 
publication Newton made the important discovery of the decom- 
position of light, and treated various optical problems with 
great precision by mathematical means. Our term /ight is re- 
lated to the Sanskrit /o#, to see. Heat has not existed as an ex- 
perimental science for a century. The science has made great 
progress during the last thirty years. Heat was once believed 
to be an entity, a kind of matter, which passed from one sub- 
stance to another, and which effected certain changes during its 
transference. We now know that it is simply a kind of motion 
akin to that which constitutes light, so that it ceases to be 
matter, and becomes an attribute of matter. It is strange that 
the term /eat should be far more appropriate now than it was 
when heat was regarded as matter, although it was in use long 
before any theory or science of heat existed. The term appears 
to be derived from the Sanskrit zvd@i, to kindle, through the 
Greek atw, the Latin esfws, and the old High German evt. 
‘* #stus,” says Vossius,” est commotio vel in aqua, vel in igni, 
vel in animo, omnis autem commotio feryorem gignit.” And 
the result of modern research has been to prove that what we 
call heat is, indeed, due to a commotion of particles of matter. 
Certain properties of heat were well known to the ancients, 
although the science itself isso young. Thus, Pliny states that 
the sacred fire of Vesta was kindled by reflecting the rays of the 
sun by mirrors. The story of Archimedes and the Roman fleet 
is well known to you. Lenses were known and were used as 
burning glasses. Aristophanes clearly alludes to the use of a 
glass lens for obtaining fire ; a lens was found among the ruins 
of Nineveh, and is now in the British Museum. Lactantius 
states that fire may be kindled by passing the rays of the sun 
through a glass globe filled with water. 
Magnetism has existed for about 270 years as an experimental 
science. A few magnetic experiments are mentioned by Lucre- 
tius, and by Pliny, and one or two Middle Age writers allude to 
the effects. Of course the mariner’s compass, which was known 
in Europe in the twelfth century, called attention to the exis- 
tence of the so-called magnetic force. The birth of the science 
dates from the publication by Gilbert of Colchester of a treatise 
entitled ‘‘ De Magnete,” in 1600. 
Thales, of Miletus, observed that amber when rubbed ac- 
quired the property of attracting light substances, and as the 
Greek for amber is #Aétpov, and the effect had not been ob- 
served in other substances, a new science arose called Electricity ; 
but the science has scarcely existed for more than 200 years. 
The inventor of the air-pump, Otto von Guericke, was also the 
inventor of the electrical machine. Thus Pneumatics and 
Electricity were called into existerce at almost the same time. 
Note how essential the invention of apparatus has been to the 
different sciences. Until experiments could be tried, and until 
instruments were devised for trying them, the natural sciences 
made no progress. Voltaic Electricity, or Galvanism, dates 
from the commencement of this century, and electro-magnetism 
and dia-magnetism are yet later developments. 
We learn from the above remarks that, although some of the 
fundamental facts of various sciences were known to the ancients, 
they never developed them, In fact, there was no experimental 
NATURE 



[ Sepé. 28, 1871 
science among the ancients, they by chance lighted upon a few 
solitary facts, and with these they were well content. There 
could be no experimental science among them, for the funda- 

7 
: 
i 
mental feature of this kind of knowledge is, that it depends upon ~ 
the action of the mind upon matter, while the ancients preferred 
to exercise their intellects upon things not external to themselves. 
Physical philosophy is distinguished from mental philosophy by ; 
the fact that the former is based upon observed results obtained 
by the action of the mind aided by experiment, upon external 
matter, while the latter is based upon the actions of the mind upon 
itself according to definite laws instituted by the unaided intellect. 
The ancients elaborated the most admirable systems of mental 
philosophy, but they refused to have anything to say to experi- 
mental philosophy. We may take the following remarks of 
Seneca as to some extent an exemplification of the spirit in 
which the ancients regarded Natural Philosophy :—‘‘ The 
astronomer tells me of Saturn and Mars in opposition, but I say, 
let them be as they will, their courses and their positions are 
ordered them by an unchangeable decree of fate. Either they 
produce and point out the effects of all things, or else they signify 
them. If the former, what are we the better for the knowledge 
of that which must of necessity come to pass? If the latter, 
what does it avail us to foresee what we cannot ayoid? So that 
whether we know or not know, the event will still be the same ;” 
as if he said in the language of more modern science, “I am 
assured that the specific gravity of iron is somewhat more than 
that of manganese, and somewhat more than that of copper, but 
I know they are immutable, and it hence matters not how they 
differ.” Or again, ‘*I am told that there are iron and sodium in 
the sun, but I can never be there to verify it, therefore it cannot 
concern me.” The ancients were content with the truths which 
they possessed, and cared not to seek for the discovery of new 
truths. Thus, as I before said, they possessed no system of 
experimental science. 
You will perhaps ask me why physical truths cannot 
be discovered by means of the unaided intellect. Why is 
experiment necessary? We must remember that our senses, 
although infinitely more perfect than our most delicate and 
refined scientific instruments, are limited in their capabilities. 
They are devoted to the service of our organisms, and exist for 
the purpose of enabling us to fulfil all the conditions requisite for 
the maintenance of life, and to make us cognisant of the external 
actions of the material world. But this latter function they 
exercise only to the necessary extent. There are numberless 
phenomena beyond the direct cognisance of the senses ; there is, 
if I may so express it, light which is unseen by the eye, sound 
which is unheard by the ear, heat which is unfelt by the nerves 
of touch. I mean there are physical actions of the same nature 
as those which constitute light, sound, and heat, which we cannot 
directly recognise. It then becomes necessary to call in the aid 
of experiment and of various instruments to assist and exalt the 
action of the senses. We have a familiar example of this in the 
microscope. A speck which the unaided eye recognises with 
difficulty, is seen by exalting the capabilities of the eye in one 
particular direction to be a perfectly organised being, possessing 
many of the functions of creatures far higher in the scale of 
animal life. One of the Infusoria measures about the twenty- 
two thousandth of an inch in diameter, and can only be seen by 
the aid of a powerful microscope, yet it is a perfectly-organised 
creature. So also, when we wish to examine the various pro- 
perties of matter, it is absolutely necessary for us to aid the in- 
tellect and the senses by means of instruments and experiments, 
The properties of matter were utterly unknown to the ancients, 
because they relied upon the unaided intellect, and disdained ex- 
periment. Numberless effects in nature reveal themselves only 
when an unnatural and forced condition is imposed upon matter, 
**Occulta Nature,” says Francis Bacon, ‘‘magis se produnt per 
yexationes artium quam cum cursu suo meant.” 
Although many observers existed before the seventeenth cen- 
tury, there were but few experimenters. Observation, experi- 
ment, and reasoning, must go hand in hand, before experimental 
science can progress. We first find this combination in a very 
marked degree in Galileo, a professor in the University of Pisa, 
who was born in 1564, and wrote in the early part of the next 
century. He invented the telescope and thermometer ; demon- 
strated the theory of Copernicus, which asserted that the sun is 
the centre of our system, and that the earth moves round it ; dis- 
covered the satellites of Jupiter and the spots on the surface of 
the sun, and, in a word, made the first real progress in many of 
the sciences, Galileo is often called the ‘‘ Father of the Expe- 
rimental Sciences ;” it is certain that he was the first experi- 
