Micrographia / Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries Thereupon

by Robert Hooke

Observ. [57]. Of Vinegar-worms.

A description of them, with some considerations on their motions.

Obs. [58]. Of the Inflection of the Rays of Light in the Air.

A short rehearsal of several Phænomena. An attempt to explicate them: the supposition founded on two Propositions, both which are indeavoured to be made out by several Experiments, What density and rarity is in respect of refraction: the refraction of Spirit of Wine compared with that of common Water: the refraction of Ice. An Experiment of making an Undulation of the Rays by the mixing of Liquors of differing density. The explication of inflection, mechanically and hypothetically: what Bodies have such an inflection. Several Experiments to shew that the Air has this propriety; that it proceeds from the differing density of the Air: that the upper and under part of the Air are of differing density: some Experiments to prove this. A Table of the strength of the spring of the Air, answering to each degree of extension; when first made, and when repeated. Another Experiment of compressing the Air. A Table of the strength of the Air, answering to each compression and expansion; from which the height of the Air may be suppos’d indefinite; to what degree the Air is rarifi’d at any distance above the Surface of the Earth: how, from this, Inflection is inferr’d; and several Phænomena explain’d. That the Air near the Earth is compos’d of parts of differing density; made probable by several Experiments and Observations; how this propriety produces the effects of the waving and dancing of Bodies; and of the twinkling of the Stars. Several Phænomena explicated. Some Quæries added.

1. Whether this Principle may not be made use of, for perfecting Optick Glasses? What might be hoped from it if it were to be done?

2. Whether from this Principle the apparition of some new Stars may not be explicated?

3. Whether the height of the Air may be defin’d by it?

4. Whether there may not sometimes be so great a disparity of density between the upper and under parts of the Air, as to make a reflecting Surface?

5. Whether, if so, this will not explicate the Phænomena of the Clouds. An Experiment to this purpose?

7. Whether the Rayes from the top of Mountains are not bended into Curve-lines by inflection? An Argument for it, taken from an Experiment made on St. Paul’s Steeple.