Category: Science - Physics
When italics were used in the original book, the corresponding text has been surrounded by _underscores_ except in the case of single letter variables used in the Notes section, where the italics were not represented. Mixed fractions have been displayed with a hyphen between w...
NOTE 120, p. 45. _Ellipsoid of revolution._ A solid formed by the revolution of an ellipse about its axis. If the ellipse revolve about its minor axis Q D, fig. 6, the ellipsoid...
46. Part 46NOTE 15, p. 4. _Mean radius of the earth._ The distance from the centre to the surface of the earth, regarded as a sphere. It is intermediate between the distances of the centre...
49. Part 49NOTE 169, pp. 109, 192, 273. _A rhombohedron_ is a solid contained by six plane surfaces, as in fig. 63, the opposite planes being equal and similar rhombs parallel to one anoth...
47. Part 47NOTE 66, pp. 16, 17. In fig. 15 the central force is greater than the exact law of gravity; therefore the curvature P p a is greater than P p A the real ellipse; hence the plane...
43. Part 43Certain rays, which exist in the sun’s light, are wanting in the spectra of every coloured star, and probably never existed in the light of these stars, as there is no reason to...
45. Part 45The fall of meteoric stones is much more frequent than is generally believed. Hardly a year passes without some instances occurring; and, if it be considered that only a small p...
13. Part 13It is a permanent and universal law in vast numbers of unorganised bodies that their composition is definite and invariable, the same compound always consisting of the same elem...
11. Part 11The particles of water under the moon are more attracted than the centre of gravity of the earth, in the inverse ratio of the square of the distance. Hence they have a tendency...
39. Part 39On the first appearance of Halley’s comet, early in August 1835, it seemed to be merely a globular mass of dim vapour, without a tail. A concentration of light, a little on one...
38. Part 38A body acquires heat in the exact proportion that the adjacent substances become cold, and when heat is absorbed by a body it becomes an expansive force at the expense of those...
5. Part 5The little that is known of the theories of the satellites of Saturn and Uranus is, in all respects, similar to that of Jupiter. Saturn is accompanied by eight satellites. The s...
16. Part 16WHEN the particles of elastic bodies are suddenly disturbed by an impulse, they return to their natural position by a series of isochronous vibrations, whose rapidity, force, an...
25. Part 25The effect of the earth’s atmosphere on lunar heat is remarkable. Professor Forbes proved that the direct light of the full moon is incapable of raising a thermometer the one th...
6. Part 6Planets sometimes eclipse one another. On the 17th of May, 1737, Mercury was eclipsed by Venus near their inferior conjunction; Mars passed over Jupiter on the 9th of January, 1...
14. Part 14Besides these small undulations, there are vast waves perpetually moving over the continents and oceans in separate and independent systems, being confined to local, yet very ex...
18. Part 18We know of no substance that is either perfectly opaque or perfectly transparent. Even gold may be beaten so thin as to be pervious to light. On the contrary, the clearest cryst...
40. Part 40Though already so well acquainted with the motions of comets, we know nothing of their physical constitution. A vast number, especially of telescopic comets, are only like cloud...
24. Part 24A series of experiments by Sir John Herschel have disclosed a new set of obscure rays in the solar spectrum, which seem to bear the same relation to those of heat that the photo...
50. Part 50NOTE 204, p. 180. Fig. 62 represents a prismatic crystal of tourmaline, whose axis is A X. The slices that are used for polarising light are cut parallel to A X.
20. Part 20Light is said to be polarized, which, by being once reflected or refracted, is rendered incapable of being again reflected or refracted at certain angles. In general, when a ray...
19. Part 19It is supposed that the particles of luminous bodies are in a state of perpetual agitation, and that they possess the property of exciting regular vibrations in the molecules of...
36. Part 36Magnetism a Dual Power—Antithetic Character of Paramagnetism and Diamagnetism—The Earth Paramagnetic—Properties of Paramagnetic Bodies—Polarity—Induction—Lines of Magnetic Force...
42. Part 42Sometimes stars have all at once appeared, shone with a bright light, and vanished. Several instances of these temporary stars are on record. A remarkable one occurred in the ye...
31. Part 31A body charged with electricity, although perfectly insulated, so that all escape of electricity is prevented, tends to produce an electric state of the opposite kind in all bod...
26. Part 26This theory perfectly accords with the phenomena of nature, since there are very few active volcanoes at a distance from the sea, and the exceptions that do occur are generally...
44. Part 44Double nebulæ are not unfrequent in both hemispheres, exhibiting all the varieties of distance, position, and relative brightness, with their counterparts the double stars. The...
27. Part 27The isothermal lines, or such as pass through places where the mean annual temperature of the air is the same, do not always coincide with the isogeothermal lines, which are tho...
41. Part 41The celestial bodies might move in any one of these four curves by the law of gravitation: but, as one particular velocity is necessary to produce either circular or parabolic m...
7. Part 7THE parallax of a celestial body is the angle under which the radius of the earth would be seen if viewed from the centre of that body; it affords the means of ascertaining the...
35. Part 35A very powerful horseshoe magnet, formed of twelve steel plates in close approximation, is placed in a horizontal position. An armature, consisting of a bar of the purest soft i...
2. Part 2Attraction of a Sphere—Form of Celestial Bodies—Terrestrial Gravitation retains the Moon in her Orbit—The Heavenly Bodies move in Conic Sections—Gravitation Proportional to Mass...
28. Part 28Terrestrial Heat—Radiation—Transmission—Melloni’s experiments—Heat in Solar Spectrum—Polarization of Heat—Nature of Heat—Absorptions—Dew—Rain—Combustion—Expansion—Compensation P...
9. Part 9The rotation of the earth, which determines the length of the day, may be regarded as one of the most important elements in the system of the world. It serves as a measure of ti...
30. Part 30Besides the temperature indicated by the thermometer, bodies absorb heat, and their capacity for heat is so various that very different quantities of heat are required to raise...
10. Part 10Such is the secular motion of the equinoxes. But it is sometimes increased and sometimes diminished by periodic variations, whose periods depend upon the relative positions of t...
3. Part 3Suppose two planets moving in ellipses round the sun; if one of them attracted the other and the sun with equal intensity, and in parallel directions (N. 62), it would have no e...
34. Part 34The next step was to make a magnet, and also a cylinder, revolve about their own axes, which they do with great rapidity. Mercury has been made to rotate by means of Voltaic ele...
8. Part 8That prediction has been fulfilled since the seventh edition of this book was published. Not only the existence of Neptune, revolving at the distance of three thousand millions...
21. Part 21It has been observed, that when a ray of light, polarized by reflection from any surface not metallic, is analyzed by a doubly refracting substance, it exhibits properties which...
37. Part 37No doubt the magnetic lines of force in the earth are closed curves, as in artificial magnets; but in their circuitous courses they may extend to any distance in space, or rathe...
22. Part 22THE numerous phenomena of periodical colours arising from the interference of light, which do not admit of satisfactory explanation on any other principle than the undulatory th...
4. Part 4Notwithstanding the permanency of our system, the secular variations in the planetary orbits would have been extremely embarrassing to astronomers when it became necessary to co...
29. Part 29It was shown, in the same section, that if light polarized by reflection from a pane of glass be viewed through a plate of tourmaline, with its longitudinal section vertical, an...
17. Part 17A musical string gives a very feeble sound when vibrating alone, on account of the small quantity of air set in motion; but when attached to a sounding-board, as in the harp and...
33. Part 33Mr. Grove considers that the colour of the voltaic arc, or flame, which appears between the poles of a very powerful battery, depends upon the substance of the metal from whence...
12. Part 12Kotzebue and Sir James Ross found a stratum of constant temperature in the ocean at a depth depending upon the latitude: at the equator it is at the depth of 7200 feet, from whe...
15. Part 15All mere noises are occasioned by irregular impulses communicated to the ear; and, if they be short, sudden, and repeated beyond a certain degree of quickness, the ear loses the...
1. Part 1When italics were used in the original book, the corresponding text has been surrounded by _underscores_ except in the case of single letter variables used in the Notes section,...
23. Part 23Not only the intensity but the kind of action is different in the different points of the solar spectrum, as evidently appears from the various colours that are frequently impre...
32. Part 32Captain Bonnycastle, coming up the Gulf of St. Lawrence on the 7th of September, 1826, was roused by the mate of the vessel in great alarm from an unusual appearance. It was a s...
51. Part 51Arago, François, experiment by, in proof of the undulatory theory of light, 200; decisive experiment suggested by, 202; observations in photography, 213; observations on the moo...
53. Part 53Gases, conditions retaining matter in the form of, 104, 105; combinations of, 111; transmission of radiant heat through, 258; expansion of, 271; voltaic spectrum modified by, 30...
56. Part 56Sirius, the Egyptian year estimated from, 85; comet’s tail extending from the Hare to, 373; rank of, 384; comparative magnitude, 385; parallax, 389; cause of his irregular motio...
55. Part 55Oscillations, wide-spreading, produced by gravitation, 2; mechanical principle affecting small, 11; of the sines and cosines of circular arcs, 20; invariable plane whence they m...
54. Part 54Light, rate of its velocity, 31; truth deduced from the uniformity of its velocity, 32; from the aberration of, _ib._; period required to reach the earth from α Centauri, 54; ac...
52. Part 52Crystallization defined, 106; forms of, their variety affected by temperature, 107, 108; permanent and variable forms, 108, 109; cleavages in, 109; common to all substances, _ib...
57. Part 57Wheatstone, Professor, experiments in acoustics of, 132; musical instruments invented by, 143; paper on musical vibrations read by, 145; experiments on sounding boards of, 150;...