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tion of heat by convection. He ought to know by heart the numbers expressing the relative conductivity of gold, silver, copper, iron, and lead.

He ought to be acquainted with the low power of conduction of organic substances; to know the effect of mechanical texture on the transmission of heat, and to explain the function of clothes in preserving the body from cold.

He ought to be acquainted with the character and phenomena of combustion; to be able to explain the chemical actions which occur in the combustion of coal and of ordinary gas, and to explain the manner in which a candle flame receives its supply of combustible matter.

The combustion of the diamond and Newton's prediction regarding it ought to be known to the pupil. That animal heat is due to slow combustion ought also to be made known.

The structure of an ordinary gas flame ought to be pointed out, and the cause of the difference between this flame and that of a Bunsen's burner explained.

The pupil must be acquainted with the general phenomena of radiant heat. The similarity between the phenomena of radiant heat and those of light, as regards reflection and refraction, ought to be known to the pupil.

The different powers possessed by different substances to radiate heat ought to be pointed out, and this knowledge ought to be applied in explaining the striking fact that the cooling of a vessel may, under certain circumstances, be hastened by surrounding it with flannel.

The reciprocity of radiation and absorption ought to be known to the pupil.

He ought also to know what is meant by the term diathermancy, and to be able to point out how this property is manifested by different bodies.

SECOND STAGE, OR ADVANCED COURSE.

Questions may be set in all subjects enumerated under the Elementary Stage, and in addition on the following topics: :

Acoustics.

The second course in acoustics includes an intimate knowledge of all the subjects mentioned in the first. In addition to this a knowledge of the following subjects will be required :

The augmentation of the velocity of propagation of a wave of sound through air by the condensation and rarefaction of the sound-wave itself.

Harmonic tones, their generation and their function in music.
The laws which regulate the transverse vibrations of rods.
The vibrations possible to a tuning-fork, a disc, and a bell.
The formation of Chladni's figures.

The laws which regulate the longitudinal vibrations of strings and rods. By a comparison of the notes emitted by a rod and a column of air the pupil ought to be able to determine the relative velocities of sound through both substances.

The conditions and cause of resonance ought to be known to the pupil.

He ought also to know how sounds are produced by the vocal organs of man, and to see clearly the similarity between such sounds and those of the syren. As a case of the same kind, the construction and explanation of the Æolian harp ought also to be known to the pupil.

He ought to be well acquainted with the principles of interference as applied to sound.

He ought to be acquainted with the principles of harmony, to know the ratios of the vibrations corresponding to the notes of the gamut, to be able to give a clear account of the bearing of interference upon the question of consonance or dissonance, and to explain why those ratios which are represented by small whole numbers correspond to the most perfect harmony.

Light,

The candidate in the second course must be intimately ac quainted with all the subjects mentioned in the first.

He must be able to apply his knowledge of total reflection to the explanation of the mirage of the desert.

He must be able to describe experiments by which white light may be produced by the admixture of its constituents.

He must know what is meant by achromatism.

He must be able to give a clear description of the undulatory theory, and to state how the colours of the spectrum are accounted for by that theory.

He must be able to define a ray of light in accordance with the undulatory theory.

He must be able to show how the reflection and refraction of light occur according to the undulatory theory.

He must be able to describe the appearances presented when incandescent metallic vapours are analyzed by the prism. Especially must he be able to state what occurs when a sodium flame is thus analyzed.

He must also be able to state what occurs when white light is transmitted through a sodium flame, and he must be able to describe an experiment which shall render manifest what occurs. He must be able to state generally the relation that subsists between radiation and absorption by gases and vapours.

The lines of Frauenhofer must be known to the pupil, and from this knowledge, in conjunction with the knowledge demanded by the foregoing paragraphs, he must be able to infer the probable constitution of the sun.

The pupil ought also to know the principles of interference as applied to light.

He ought to be able, in accordance with these principles, to account for the colours of thin plates and of striated surfaces. The general principles of diffraction ought to be known to the pupil.

He ought to know what is meant by plane polarized light; to describe the act of polarization in the language of the undulatory theory.

He ought to know what occurs when a beam of light is transmitted through a crystal of Iceland spar, and to describe the state of the emergent light as regards polarization.

He ought to be able to describe the effects observed when light is transmitted through two plates of tourmaline cut parallel to the axis of the crystal.

He ought to be able to describe some form of the polariscope, and to state and explain by the principles of interference what occurs when a thin plate of selenite is placed between the polarizer and analyzer.

Heat.

The candidate in the second course must be intimately acquainted with all the subjects introduced into the first.

He ought to be able to give a clear statement of the mechanical theory of heat as distinguished from the material theory.

He must know what is meant by the "mechanical equivalent of heat," and how it has been determined.

He must know what is meant by specific heat at constant volume and at constant pressure, and have in his memory the numerical ratio of the two specific heats.

He ought to be able not only to explain the meaning of the difference between the two specific heats in accordance with the mechanical theory, but also to show how from this ratio the mechanical equivalent of heat may be determined.

Given the weight and velocity of à moving body, he ought to

be able to calculate the amount of heat generated by the stoppage of the motion.

He ought to be able to apply the conceptions of the mechanical theory to the phenomena of combustion.

He ought also to be able to show the bearing of the theory upon the phenomena of specific and latent heat.

EXAMINATION FOR HONOURS.

The candidate for honours must be intimately acquainted with the foregoing two courses. He must also show himself practically acquainted with the apparatus employed in acoustics, light, and heat.

PREFACE TO THE FIFTH EDITION.

SOME years ago I was encouraged to write a small Text-Book for the instruction of a class in Natural Philosophy. When the subject of scientific instruction. was taken up by the Science and Art Department I endeavoured to make my books useful in facilitating the attainment of sound elementary knowledge in science. My official work in connection with the Department, now extending over a period of fifteen years, has prevented my giving that attention to a revision of the books which from time to time appeared necessary. I felt the best thing I could do was to secure the co-operation and help of the most experienced and successful teachers of the sciences to which the books relate, so as to make them worthy the object for which they have been prepared.

J. C. BUCKMASTER.

St. John's Hill, Wandsworth, S. W.,

January, 1871.

THE ELEMENTS

OF

ACOUSTICS, LIGHT, AND HEAT.

ACOUSTICS.

SOUND is caused by the mechanical vibrations of an elastic body, which are transmitted by undulations through the atmosphere or some other medium to the ear. The vibratory body is said to be sonorous. If a glass tumbler be gently struck with any hard body, a tremulous agitation is communicated to the entire mass. The surrounding air is thrown into corresponding waves, which strike upon the tympanum or drum of the ear, producing a vibratory motion in that delicate membrane. This motion is again communicated to the brain by the auditory nerve, giving the sensation of hearing. We hear, then, by means analogous to those by which we see; for in a similar manner the waves of light strike the eye, and are conveyed by the optic nerve to the brain. Suppose a stretched cord, represented by the line A B C, Fig. 1, to be drawn aside to D; in returning to its original position it does so with a momentum which carries it past the line A B C to A E C, from which it returns again nearly to A D C, and so backward and forward, until, after a number of oscillations, it comes to a state of

B

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