Science waxed and waned around the Mediterranean Sea from the end of Classical times until 1500; as an art, it reached a peak in cultural quality with the Greeks and its greatest extent in the Roman Empire. After its decline in Greece and Rome, science became ascendent with the Arabs south of the Mediterranean. in the 12th century, science declined with Arabs and rose in christian Europe, reaching another peak in theh 13th century with St. Thomas Aquinas.

By the 12th century, communication was better, allowing more widespread transfer of ideas. Fundamental to better communication was the development of the magnetic compass and the clock, which allowed men to synchronise their activities in space and time.

Changes in the state of knowledge are not sudden, all current knowledge depends on all prior research; though we erect artivicial divisions to history, the movement from one phase to the next is gradual.

• Muslim al-Ghazzali lived from the year 1058 until 1111.
• Jewish Maimonides lived from the year 1135 until 1204.
• Christian St. Thomas Aquinas lived from the year 1225, approximately, until 1274.
• Leonardo da Vinci lived from the year 1452 until 1519.
• Roger Bacon lived from the year 1214 until 1294.
• Buridan lived, approximately, from 1297 until 1358.
• Botticelli lived from 1444 until 1510.
• Albrect Dürer lived from 1471 until 1528
• Brunelleschi lived from 1379 until 1446.

Development of science was erratic; discoveries were made and lost and rediscovered again; science develooped from several different sources, sometimes hampered by the prevailing theories, at other times and places greatly encouraged. Science was limited in its development by the difficulty of recording and distributing ideas; all writing was at first manuscript and books were rare and very expensive. Leonardo da Vinci's work remained hidden because he never published his notebooks; we are lucky to discover these notebooks because da Vinci consigned them to the care of one of his students. Development of science was hampered by secrecy and mysticism, an unwillingness to share knowledge — a miserliness.

Condition of individual sciences between 1450 and 1500 were:

• Physics was completely undeveloped.
• Sound was the arithmetic of music.
• Magnetism was untouched despite the need to navigate.
• Electricity consisted in some observations on static electricity generated by rubbing amber.
• Heat was a branch of alchemy.
• Biology, optics, and mechanics were the interests of great artists. Study of biology for realism in art, optics for perspective, and mechanics for movement.

Convex spectacles of Venetian glass were becoming more common in 1300; concave lenses were not common until the middle of the 16th century.

Clocks were developed first to regulate the periods of prayer for religion. Timekeeping became necessary to business.

Chemistry developed from alchemy.

Optics and astronomy were exercises in geometry.