Nevertheless, when we compare these classifications diligently, we find very marked differences between Bacon's views and the medieval. The weakest part of Hugo's classification is that which deals with natural philosophy. _Physica_, he says, undertakes the investigation of the causes of things in their effects, and of effects in their causes. It deals with the explanation of earthquakes, tides, the virtues of plants, the fierce instincts of wild animals, every species of stone, shrub, and reptile. When we turn to his special work, however, on this branch of knowledge, _Concerning Beasts and Other Things_, we find no attempt to subdivide the field of _physica_, but a series of details in botany, geology, zoölogy, and human anatomy, mostly arranged in dictionary form. When we refer to Bacon's classification we find that Physics corresponds to Hugo's _Physica_. It studies natural phenomena in relation to their material causes. For this study, Natural History, according to Bacon, supplies the facts. Let us glance, then, at his work on natural history, and see how far he had advanced from the medieval toward the modern conception of the sciences. For purposes of scientific study he divided the phenomena of the universe into (1) Celestial phenomena; (2) Atmosphere; (3) Globe; (4) Substance of earth, air, fire, water; (5) Genera, species, etc. Great scope is given to the natural history of man. The arts are classified as _nature modified by man_. _History_ means, of course, descriptive science. _Bacon's Catalogue of Particular Histories by Titles (1620)_ 1. History of the Heavenly Bodies; or Astronomical History. 2. History of the Configuration of the Heavens and the parts thereof towards the Earth and the parts thereof; or Cosmographical History. 3. History of Comets. 4. History of Fiery Meteors. 5. History of Lightnings, Thunderbolts, Thunders, and Coruscations. 6. History of Winds and Sudden Blasts and Undulations of the Air. 7. History of Rainbows. 8. History of Clouds, as they are seen above. 9. History of the Blue Expanse, of Twilight, of Mock-Suns, Mock-Moons, Haloes, various colours of the Sun; and of every variety in the aspect of the heavens caused by the medium. 10. History of Showers, Ordinary, Stormy, and Prodigious; also of Waterspouts (as they are called); and the like. 11. History of Hail, Snow, Frost, Hoar-frost, Fog, Dew, and the like. 12. History of all other things that fall or descend from above, and that are generated in the upper region. 13. History of Sounds in the upper region (if there be any), besides Thunder. 14. History of Air as a whole, or in the Configuration of the World. 15. History of the Seasons or Temperatures of the Year, as well according to the variations of Regions as according to accidents of Times and Periods of Years; of Floods, Heats, Droughts, and the like.