Page:Popular Science Monthly Volume 87.djvu/285 NATURAL SCIENCE
IN THE MIDDLE ACES 281 Though naked unassisted eyes Can scarce
perceive them. Grains of sand Seem stones when through these
glasses scanned. The poet goes on to say that through these
glasses one can read letters from such a distance that one would
not believe it unless he had seen it. Then he concludes, But to
these matters blind affiance No man need give; they're proved by
science. From the testimony of several other contemporaries we
know that eye-glasses had been invented before the close of the
thirteenth century. Another important physical treatise besides
Witelo's was a " Book on Weights " by Jordanus Nemorarius
earlier in the century. In this work he is said to have made
progress in dynamics beyond the ancients. Another invention of
great use to science, clocks, was worked out during the middle
ages. An innovation of great convenience in scientific reckoning
and records was made when Leonardo, a merchant of Pisa, in a
work written first i