elements of optics answering to the phenomena in nature.--_Ed._ [151] As far as this motion results from attraction and repulsion, it is only a simple consequence of the last two.--_Ed._ [152] These two cases are now resolved into the property of the capillary tubes and present only another feature of the law of attraction.--_Ed._ [153] This is one of the most useful practical methods in chemistry at the present day. [154] See Aphorism xxv. [155] Query? [156] Observe this approximation to Newton’s theory. [157] Those differences which are generated by the masses and respective distances of bodies are only differences of quantity, and not specific; consequently those three classes are only one.--_Ed._ [158] See the citing instances, Aphorism xl. [159] Aristotle’s doctrine, that sound takes place when bodies strike the air, which the modern science of acoustics has completely established, was rejected by Bacon in a treatise upon the same subject: “The collision or thrusting of air,” he says, “which they will have to be the cause of sound, neither denotes the form nor the latent process of sound, but is a term of ignorance and of superficial contemplation.” To get out of the difficulty, he betook himself to his theory of spirits, a species of phenomena which he constantly introduces to give himself the air of explaining things he could not understand, or would not admit upon the hypothesis of his opponents.--_Ed._ [160] The motion of trepidation, as Bacon calls it, was attributed by the ancient astronomers to the eight spheres, relative to the precession of the equinoxes. Galileo was the first to observe this kind of lunar motion.--_Ed._ [161] Part of the air is expanded and escapes, and part is consumed by the flame. When condensed, therefore, by the cold application, it cannot offer sufficient resistance to the external atmosphere to prevent the liquid or flesh from being forced into the glass. [162] Heat can now be abstracted by a very simple process, till the degree of cold be of almost any required intensity.--_Ed._ [163] It is impossible to compare a degree of heat with a degree of cold, without the assumption of some arbitrary test, to which the degrees are to be referred. In the next sentence Bacon appears to have taken the power of animal life to support heat or cold as the test, and then the comparison can only be between the degree of heat or of cold that will produce death. The zero must be arbitrary which divides equally a certain degree of heat from a certain degree of cold.--_Ed._ [164] It may often be observed on the leaves of the lime and other trees. [Transcriber’s Notes: