But while the atoms are described as “indivisible,” because there is no vacuum in them, this does not mean that they were regarded by Leucippus and Democritus as mere mathematical points, like the atoms of Boscovich[9] or the “point charges” (electrons) of some modern physicists. They were bodies of a definite magnitude, some larger, others smaller, but never of visible size (Sextus, _Mathematica_, vii, 139), much less, as asserted by Stobæus (_Eclagarum physicarum et ethicarum_, i, 348) “as large as a world.” According to Simplicius (_Physica_, 18 a), Democritus taught that the atoms were physically indivisible, but he did not claim that they were _mathematically_ indivisible. The variety of substances and organisms seen on every hand is due entirely, according to Democritus--and also to Leucippus, whose views are expressed by Democritus--to the infinite variety of the atoms in form, size and _arrangement in space with reference to one another_--an anticipation of modern stereochemistry (the arrangement of the atoms of a molecule in space) and the work of van’t Hoff (1852-1911).[10] In all other respects the atoms are alike, and act on one another only by pressure or collision. THE ATOMIC THEORY OF KNOWLEDGE Man’s sense impressions--color, sound, bitterness, sweetness, etc.--are merely the effect of the impact of atoms upon a particular grouping or arrangement of physically varied but essentially (chemically) homogeneous atoms, constituting our sense organs. Hence these sense qualities have no existence in themselves--are mere deceptive “appearances.” “Only in opinion consists sweetness, bitterness, cold, color; in truth there is nothing but the atoms and empty space,” says Democritus. The great Protagoras (born about 500 B. C.), also of Abdera, a contemporary of Leucippus and Democritus, had taught that all sensations are equally true for the sentient subject--i.e., if a substance tastes sweet to a given person, it is sweet. For Democritus sweetness and bitterness did not reside as such in the substance tasted, but were merely subjective effects produced on the palate of the consumer. Taste is partly dependent upon the shape of the atoms composing the food (they held) and partly upon the particular taste-sense of the individual. Thus to the normal (or average) person honey has a sweet taste, whereas the same honey to a jaundiced person has a bitter taste.