AN ANCIENT SCIENTIST. 839 



The eruption of volcanoes is referred by Lucretius to the expansion 

 of air heated in the cavities of the earth. Modern theorists would 

 rather explain their occurrence by the expansion of steam under great 

 pressure in some underground passage. 



Our author goes on with the explanation of many other phenomena. 

 But he is continually led into error by his desire to accommodate the 

 explanation of the effects to suit his theory. As a specimen, we may 

 quote his view of magnetic attraction. According to the Epicurean 

 belief, all substances gave off pellicles or effluvia, which, as before re- 

 marked, were supposed to affect the senses. When, then, a magnet 

 and a piece of iron are brought near each other, the effluvia from the 

 former drive away the air between the two bodies, and particles of 

 iron rush to fill the vacuum so caused. Since these particles are very 

 coherent, they draw the rest of the iron after them. The magnet does 

 not attract gold, because that substance is too weighty ; wood, on the 

 other hand, is so porous that the atoms of the effluvia pass through it 

 without difficulty. Amid all these absurdities he seems to have had a 

 really philosophic idea of atmospheric pressure. He says : " The sur- 

 rounding air is continually dashing upon [bodies] ; and it drives the iron 

 forward, under such circumstances [as those mentioned before], because 

 the space on one side is empty, and receives [the iron] into itself." 

 He seems also to have had a crude idea of the modern germ theory of 

 disease, and this idea he dwells upon in the closing portion of his work. 

 He describes the means by which disease is spread, and instances the 

 plague at Athens,* with ,a magnificent description of which he con- 

 cludes his poem. 



We have traced such of the principles of the author as seem to 

 bear on the relations of ancient to modern science. We see what 

 effect a false method produced in a man of undoubted genius, endowed 

 with a genuine appreciation of nature and a scientific tendency of 

 mind. Anxious for a rational explanation of every part of the won- 

 derful universe that surrounded him, he was not contented with the 

 slow processes of observation and experiment, but hastened to assign 

 the most probable a priori causes to everything. And thus, whenever 

 he states a physical truth, he appears to have stumbled upon it quite 

 accidentally. It is no reproach to modern men of science that they 

 have been anticipated in their discoveries by a Roman who lived nine- 

 teen centuries ago. Rather, it is their glory that, for the vague intui- 

 tions of the poet-philosopher, they have substituted the certainty of 

 demonstration ; and, by toilsome study in fields which the ancients 

 either neglected or despised, have gained generalizations far surpassing 

 any of his in grandeur. It is not, therefore, for any discoveries that he 

 made, still less for his method of acquiring knowledge, that we give 

 Lucretius a place in the scientific ranks ; it is rather for the high qual- 



* Broke out b. c. 430. An accurate account of it is given by Thucydides, from whom 

 Lucretius is thought to have taken his description. 



