Popular Edurator. VOLUME THE FOURTH. STON MECHANICS FISTITUTY STUDIES serve for delight, for ornament, and for ability. Their chief use for delight, is in privateness and retiring; Presented by The Hon W Savile CASSELL'S EDUCATIONAL LONDON: CASSELL, PETTER, AND GALPIN, LA BELLE SAUVAGE YARD, TO OUR READERS. IN bringing our Fourth Volume to a close, we heartily thank all our Subscribers for their steady and unwearied support. The letters of encouragement and of commendation which we have received during the past six months, have been more numerous and, more gratifying than ever. We have endeavoured to show our sense of these favours, by labouring more earnestly to impart solid and useful instruction in various important branches of learning; we have, in fact, considered that we were entrusted by our readers with the responsible task of their education, and we have aimed at fulfilling our duties to their satisfaction. We have given a concise and popular summary of the leading facts in several branches of Natural Philosophy, as may be seen by consulting the Index ; but many highly useful and interesting departments are soon to follow in their order; these are Caloric and Optics, or the doctrines of Heat and Light, including some of their most interesting applications, as the Steam Engine, the Telescope and Microscope, Daguerreotype and Photography; Magnetism and Electricity, including the nature of the Telegraph, the Electrotype, and other useful applications; and, as soon as possible, Astronomy, which is much in demand. Chemistry has also been treated in a highly popular manner, and has converted a great number of our Subscribers into practical Students of that art. The elegant languages of ancient Greece and of modern Rome have also occupied our pages, and have been expounded with great care by the authors of the Lessons on these branches of Literature; nor have we forgot our Students in French, as a "Course of Readings" in that popular language is still appearing at convenient intervals. The Mathematics, including Algebra and Geometry, with Instrumental Arithmetic and Mathematical Illustrations, have also been progressing under our own care, and these branches will be still more vigorously pursued in our next Volume, where some of them, if possible, will be brought to a conclusion. Bookkeeping has already occupied a portion of our labours, and we shall conclude this branch in a few early Numbers, with the subject of Foreign Trade. The Lessons in Reading and Elocution will be rendered still more useful and attractive in our next Volume; but we cannot promise any new language till we have finished one or more of those now in hand; the German, however, is very near a conclusion. We are preparing for Lessons in Mechanical Drawing, and in various other branches which have been unavoidably, postponed, on account of the great demand for those which we have given, and which we are now carrying on. In closing these remarks, we can only say that we shall continue to place before our Readers, as we have always striven to do, those subjects which are the most in demand, and which are calculated to do "the greatest possible good to the greatest possible number." JULETAR LXXVIII. The Infinitive; Government of Verbs; etc LXXIX. Government of Verbs; the Past Participle LXXX. Remarks on the Foregoing Rules, etc LXXXI. Adverbs of Negation; the Preposition 14 LXXXII. Syntax; the Articles; the Noun, etc................ 33 LXXXIII. Rules and Observations relating to Nouns, etc. 325 48 LXXXIV. The Pronouns; the Adjectives; the Verbs 339 LXXXV. Use of the Tenses; Rules and Observations.... 26 VIII, IX., X., XI. The Third Declension; Paradigms 10, 39, 55, 71 42 XII., XIII. The Second Declension contracted; the Three Declensions reviewed; Exercises, etc......97, 115 XIV., XV. Comparison of Adjectives; General View 124, 170 XVI. Adverbs; Comparison of Adverbs XVII., XVIII. The Pronouns; Personal; Reflective; Reciprocal; Possessive; Demonstrative; Rela- tive; Indefinite and Interrogative, etc....209, 222 XIX. The Numerals; with Declension of the First 235 XX. Numeral Adverbs; Remarks; General View.. 244 XXI., XXII. The Verb; Voices, Tenses, Moods; the 234 XIV., XV. Capillary Attraction; its Effects; Laws of the Ascent and Depression of Liquids in Capil- lary Tubes, between Plates of Glass, in Siphons; of Liquids in Contact with Solids, etc... Endosmose, Absorption, and Imbibition; Ab- sorption in Plants and Animals Pneumatics; Gases and the Atmosphere; Mag- deburgh Hemispheres; Measure of Atmo- spheric Pressure; Torricellian Experiment; XVIII. The Atmosphere; its Pressure; the Barometer, The Elastic Force of Gases; Experiments of Boyle; Mariotte's Law; Manometers ... 276 ...... V. Of Diphthongs; Third Pronouncing Table VII, VIII. Fifth Pronouncing Table IX. Sixth Pronouncing Table, Accents, etc......... X. On the use of the Apostrophe XI., XII. The Articles; Declension of Nouns XIII., XIV., XV. Use of the Preposition or case-sign XVI. Use of the Particle a; Vocabulary XVII., XVIII. Use of the Preposition Da; etc. XIX. Use of the Preposition In; etc. XX. Use of the Preposition Con; etc............................. XXII. The Condenser; Condensing Syringe; Condensed XXIII. Pumps; the Suction-Pump, Forcing-Pump, XXIV. Acoustics: Production, Propagation, and Reflec- tion of Sound; Intensity of Sound; Savart's Apparatus for Increasing Sound; Effect of Tubes; Velocity of Sound; Laws of Reflected XXV. Echoes and Ringing Sounds; the Speaking and Hearing Trumpets; Vibrations of Cords; the Monochord; Nodes and Nodal Lines; Savart's 333 349 361 356 181 225 The Semicolon; the Colon; the Parenthesis, 370 XXII. Minor Tunes; Exercises; Remarks on the Com- 273 ......... MATHEMATICAL ILLUSTRATIONS. VIII. Hydrostatics; Properties of Liquids; Piesome- X. Bodies immersed in Liquids; Principle of ON PHYSICS, OR NATURAL PHILOSOPHY.-No I. OBJECT OF THE SCIENCE. THE object of physics, or natural philosophy, is the study of all phenomena which material substances present, except those which relate to changes of internal composition; the latter come under the domain of chemistry. For example, selecting the metal iron as a subject of contemplation, we may study its specific gravity, its degree of hardness, its property of welding, of being drawn out into wire, and rolled or beaten into plates; all these phenomena depend upon the physical properties of the metal, and the study of such phenomena comes under the domain of physics, or natural philosophy, sometimes called mechanical philosophy. But iron is endowed with another set of qualities. It is capable of being dissolved in certain acids, and rendered invisible as iron, although its presence may be recognised by various tests. All this department of study belongs to chemistry. We have stated that matter (or material bodies) admits of being studied under two aspects: but what is matter? It is necessary to arrive at some understanding as to this question before proceeding farther. Perhaps the best definition of matter is comprehended in the expression, whatever falls or is capable of falling under the immediate cognisance of the senses. At this time, there are sixty-three known elementary or simple bodies; that is to say, bodies out of which chemical analysis has not succeeded in extracting more than one species of matter. Nevertheless the number sixty-three is by no means to be regarded as the permanent representative of simple bodies. Possibly their number may hereafter be increased or diminished, according as new simple bodies may be discovered, or those with which chemists are at present acquainted may be proved to be made up of simple constituents. Bodies, Atoms, Molecules.-Every definite or limited amount of matter is termed a body or mass, and the properties of such bodies or masses show that the matter of which they are composed is not continuous, but is made up of elements, as it were, infinitely small; so small that they are incapable of physical or mechanical division, and not in actual contact, but in near proximity; the distances between them being maintained by reciprocal repulsions, known under the name of molecular forces. These minute elements of bodies are termed atoms, and groups of atoms are termed molecules,—of which latter, a body or mass is only an aggregated collection. Mass.-The term mass of a body is applied to the amount of matter which it contains. The absolute mass of a body cannot be determined, but its relative mass, considered with regard to the mass of some other body taken as unity, can be readily arrived at. Physical Conditions or States in which Bodies exist.-These states are three, each being well characterized and readily distinguishable from the others. 1. The solid state. This condition is manifested at ordinary temperatures by wood, stone, and metals. It is characterized by an entire adherence of molecules amongst themselves, so that they only admit of separation by the exercise of a certain degree of force, varying for different solids, and for the same under different circumstances. It is a direct consequence of this molecular adherence, that solid bodies retain their original forms. 2. The liquid state. Of which we are furnished with examples in water, alcohol, and oils. The distinctive character of liquids is an adherence of so feeble a degree between their molecules, that the latter slide upon and pass each other with extreme facility, in consequence of which it results that liquid bodies do not affect any external form of their own, but invariably assume that of the containing vessel. 3. The gaseous state. Of this we have examples VOL. IV. in the air, and a great number of other bodies, to which the general appellation gas or aëriform fluid is applied. In gases the mobility of the molecules is still greater than in liquids; but the special characteristic of gases is their unceasing tendency to expand into a greater volume; a characteristic expressed by the term expansibility, and which will hereafter be demonstrated experimentally. The general term fluid is applied both to liquids and to gases. The greater number of simple bodies, and many compound ones, are capable of presenting themselves successively under the three forms of solid, liquid, and gaseous, according to the variations of temperature to which they are exposed. Of this successive change, water affords a well-known example. Hereafter, when we farther advance into the regions of natural philosophy, it will be found that the three states of solid, liquid and gaseous, depend chiefly on variations of molecular attraction and repulsion. On Physical Phenomena.-Every change which the state of a body may undergo without involving alteration of composition Is a physical phenomenon. The falling of a body, the sound produced by such falling, the freezing of water, all are physical phenomena. Laws and Physical Theories.-The term physical law is applied to designate the constant relation which exists between any particular phenomenon and its cause. For example, in demonstrating the fact that a given volume of gas becomes one-half, one-third, one-fourth, &c., its original size, according as it is exposed to a degree of pressure, twice, three times, &c., we illustrate the well-known physical law which is expressed by saying that the volumes of gases are in an inverse ratio to the pressures under which they exist. A physical theory is the collection of laws relating to the same class of phenomena. Thus we speak of the theory of light, the theory of electricity. Nevertheless this expression also applies, though in a more restricted sense, to the explication of certain particular phenomena. In this latter sense, we speak of the theory of daw, the theory of mirage, &c. Physical Agents.-As causes of the phenomena which bodies present, philosophers admit the existence of physical agents or natural forces, by the operation of which all matter is governed. These agents are universal attraction, caloric or heat, light, magnetism and electricity. Mere physical agents only manifest themselves to us by their effects, their ultimate nature being completely unknown. In the present state of science, the question still remains undetermined, whether the physical agents are to be regarded as properties inherent in matter, or whether they are in themselves subtle material bodies, impalpable, pervading all nature, and the effects of which are the The latter result of movements impressed upon their mass. hypothesis is that most generally admitted; but being admitted, next follows the important question,-"Are these kinds of matter distinct amongst themselves, or are we to refer them to one and the same source?" This latter opinion appears to gain ascendency in proportion as the boundaries of natural philosophy become expanded. Under the assumption that the physical agents are subtle forms of matter, devoid of all appreci able weight when tested by balances of the highest sensibility, they have been termed imponderable fluids; hence arises the distinction between ponderable matter, or matter properly so called, and imponderable matter, or imponderable physical agents. ON THE GENERAL PROPERTIES OF BODIES. Different Kinds of Properties.-By the term properties of bodies or of matter is understood, the different methods by which they 79 |