6 
t^OPTJLAR SCIEl^CE NEWS. 
tJ-' 
1S90. 
[Original in The Popular Science iVr!«s.] 
THE SCIENTIFIC KNOWLEDGE OF THE 
ANCIENT GREEKS AND ROMANS. 
BY JOHN C. ROLFE, PH. D. 
II. 
SOUND, HEAT, AND LIGHT. 
The father of the science of acoustics was the 
famous philosopher Pythagoras, who was born at 
Samos, at the end of the seventh century B. C. We 
are often told that he was led to the discovery of the 
arithmetrical relations of the musical scale by ob- 
serving accidentally the various sounds which were 
produced by hammers of different weights striking 
upon an anvil. Longfellow refers to this old story 
in his poem "To a Child": 
As great Pythagoras of yore, 
Standing beside the blacksmith's door, 
And hearing the hammers, as they smote 
The anvils with a different note. 
Stole from the varying tones that hung 
Vibrant on every iron tongue. 
The secret of the sounding wire. 
And formed the seven-chored lyre. 
But, unfortunately for the truth of the story, dif- 
ferent hammers do not produce different sounds 
from the same anvil. It seems certain, however, 
that Pythagoras invented the monochord, which is 
A NOVEL ELEVATOR. (See page 5.) 
thus the first known apparatus for the experimental 
investigation of natural laws. By means of this, he 
discovered that all intervals of sound which make a 
pleasant and harmonious impression on our ears, 
correspond to the simplest numerical relations ; 
that, for example, if a string of the length » gave 
the keynote, V2' and /i* gave the octave and the 
third. Euclides, or Euclid, the famous geometer, 
collected the results reached by Pythagoras and his 
school, giving us an aritmetical- demonstration of 
the way of dividing the scale ; while, among the 
Romans, Vitruvius and Bcethius wrote on the same 
subject, but without making any original contribu- 
tions to it. 
The first to undertake to explain the phenomena 
of sound was Aristotle. He discovered that the air 
was the medium by which all sounds were trans- 
mitted, and observed that the velocity with which 
they travelled, differed on difterent days and at dif- 
ferent seasons of the year. Vitruvius applied 
acoustic principles to the construction of theaters. 
He explains clearly that sound travels in waves 
of air, spreading in all directions from the sonorous 
body. 
Of the laws of heat, the ancients knew practically 
nothing, having a merely empirical knowledge of 
the ordinary processes of melting, freezing, boiling, 
and the like. They developed heat by burning, by 
friction, and by the concentration of the sun's rays. 
They knew that steam and air were expanded by 
heat. Aristotle, who investigated the subject, was 
prevented from accomplishing anything by assum- 
ing at the outset that heat and cold were radically 
independent things, instead of differing merely in 
degree. He seems, however, to have recognized a 
definite melting-point for various metals, and he 
explains the ready melting of "Celtic tin" by the 
weak cohesion of its molecules. He also appears to 
have had some idea of latent heat. Among the 
Romans, we find the use of a principle of heat by a 
man who, least of all, would have claimed the glory 
of being a savant — the grim old censor, Marcus 
Porcius Cato. In describing the preparation of a 
certain dish, he says that the ingredients are put 
into an earthen vessel ; this in turn is put into a pot 
full of water, which is set over the fire. Here we 
have a suggestion of the method afterwards em- 
ployed by the Arabs, and familiar in our day, for 
maintaining a given temperature in water-baths. 
In optics, far greater advances were made than in 
the two departments of physics already reviewed. 
At first, the idea of the process of sight was a wholly 
inverted one, for it was supposed that the course of 
light was from the eye to the object seen, long 
feelers going out from the organ of vision, which 
formed a conception of the object viewed by actual 
contact with its surface. Epicurus and Hipparchus 
assumed the existence of visual rays proceeding 
from the eye ; and the ancient geometers described 
spheres which resulted from the union of the beams 
from the two e3"es, those from the right eye turning 
to the left, and vice versa. They maintained that 
while the eye could take in a great many objects, a 
distinct impression was received only where the 
rays met. 
The first to write on the subject was Euclid, a 
believer in the "feeler" theory. While he made 
many errors, he showed that the angle of incidence 
is equal to the angle of reflection, and in one of his 
theorems gives the germ of the idea of linear per- 
spective. The next in order in the development of 
the subject is Cleomedes, whose work is largely a 
compilation of that of Poseidonius, a contemporary 
of Cicero. He is the first to show a knowledge of 
the principle of refraction, which he illustrates by 
the familiar experiment with the coin in water; and 
he explains the phenomenon of twilight on that 
principle. 
Ptolemains, or Ptolemy, the well-known mathe- 
matician and astronomer, wrote on the theory of 
light, and defined the angles of incidence and re- 
flection for various refracting media. While it was 
left for Descartes to discover the laws of refraction, 
Ptolemains laid the foundation for later investiga- 
tions. A work on mirrors, which was formerly 
attributed to Ptolemains, is now believed to be the 
work of the versatile Heron, who did such good 
service in the field of mechanics. He gives a de- 
scription of a heliostat, by which a ray of sunlight 
was introduced into a darkened room and kept in a 
given position ; of a mirror which distorted the 
image reflected, and of an apparatus for producing 
ghostly apparitions on the stage, similar to those 
now employed for that purpose. 
The ancients were acquainted with various opti- 
cal instruments. Mirrors were known at a very 
early period. They were made of various metals, 
and of polished stone. Nero had a mirror of emer- 
ald, and Pliny tells us that mirrors were made of 
rubies, though this stone is never found now suffi- 
ciently large for the purpose. The mirrors made at 
Brundisium, from a mixture of tin and copper, were 
celebrated. The white metal thus produced readily 
becomes dim, and a sponge with powdered pumice- 
stone was generally fastened to them for renewing 
the polish. The use of silver mirrors was very 
common at Rome. Glass mirrors are spoken of by 
Pliny and others. 
Burning-glasses were known at Athens as early 
as the time of the Peloponnesian war, for Aristo- 
phanes makes one of his characters use one to 
obliterate a charge against him which was recorded 
on a wax tablet. The burning-glasses of Archime- 
des have already been referred to. This instrument 
was also used by the vestal virgins to rekindle the 
sacred fire, if, by any unhappy chance, it was ex- 
tinguished. 
Magnifying-glasses were known to the Romans, 
and the short-sighted emperor Nero is said to have 
used one at the theater. This instrument was sim- 
ilar to our modern spectacles or eye-glasses, rather 
than to opera-glasses. The vexed question whether 
anything corresponding to the opera-glass or the 
telescope was known to the ancients, seems to have 
been answered in tlie negative, although they may 
have used an empty tube to aid their sight in cer- 
tain cases. 
The question whether the sense of color of 
the ancients was less developed than our own, has 
been much discussed, and the attempt has been 
made to prove that Homer was partially color- 
blind. Aristotle distinguished only three — or at 
most four — colors in the rainbow, though he could 
probably have passed a modern examination for 
color-blindness. 
The subjects of magnetism and electricity must be 
left for another paper. 
[Note. — The December number, containing the first article 
of this series, will be sent free to anv 7iew subscrilier requesting 
it.l 
EIKOXOGEN, A NEW PHOTOGRAPHIC 
DEVELOPER. 
Andressen, of Berlin, has discovered a new sub- 
stance to which he has given the name of eikonogen 
or ikonogen, and which is manufactured in Ger- 
many. This is a substance derived from anilin, like 
hydroquinon, of a greenish gray color, sensitive to 
light, and non-crystallizable. According to M. 
L'llote, it is distinguishable from hydroquinon by 
means of fuming nitric acid, whichacts slowly upon 
the latter body, blackening the crystals and forming 
an oxide, yellow and slightly soluble; while it acts 
very energetically upon eikonogen, forming a yel- 
low colored matter which turns red with water. 
Eikonogen can replace hydroquinon for the devel- 
opment of photographic images. The following 
formulas may be used : 
FORMULA NO. I. 
Sulphite of soda 100 grammes 
Distilled water 1500 grammes 
Eikonogen 25 grammes 
FORMULA NO. 2. 
Distilled water ^ao grammes 
Carbonate of soda 74 grammes 
Three parts of the first solution is taken with one 
part of the second. 
To hurry the development, add a few drops of the 
following accelerator : 
Carbonate of potash 10 grammes 
Distilled water , . . 100 grammes 
To restrain the development, add a few drops of 
the following retardator: 
