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MAP OF AFRICA.
31° 21' N. 30 6 E. Accra, Guinea
0 13 W. Anamaboo, Guinea
1 7 7 Angra Pequena, West Africa 26 39 S. 15 3 E. Apollonia Cape, Guinea
4 44 N.
2 33W, Axum, Abyssinia
14 30 38 40 E. Bubelmandeb Peak, E, Africa 12 42
32 Barbara Point, West Africa 15 55 16 33 W Bathurst, West Africa
16 35 Bambouk, West Africa .... 13 35 10 50 Bengazi, Tripoli..
20 3E Bianco Cape, Tunis
9 48 Bizerta, Tunis..........
9 49 Blanco Cape, Morocco
8 Bojador Cape, West Africa 26 7
1 31 Bomba, Tripoli
32 24 23 11 E Bona, Algeria..
7 48 Bon Cape, Tunis
11 2 Braya, East Africa
43 58 Cabes, Tunis
83 53 10 4 Cantin Cape, Morocco
9 13 W Ceuta, Morocco ......
5 17 Corrientes Cape, East Africa | 24 8
85 25 E Cosire, Egypt
26 7S. 34 21 Cyrene, Tripoli
32 80 N. 21 49 Damietta, Egypt
31 50 Delgado Cape, East Africa 10 41 s. 40 35 Dendera, Egypt..
26 10 N. 32 40 Derna, Tripoli
22 41 El Arish Fort, Egypt
88 48 Falcon Cape, Algeria
0 48W. Ferro Cape, Algeria
5 Formosa Cape, West Africa
6 5. Frio Cape, West Africa... 18 23S, 11 67 Guardafui, East Africa
11 41 N.
51 12 Hammamet, Tunis.
10 89 Jerba I, Tripoli,
38 53 10 63 Join (St.) Cape, West Africa 1 10
9 18 Kudia, Tripoli..
30 44. 18 11 Lamoo, East Africa
2 16 S. 40 51 Lagos R., West Africa
6 26 N. 3 22 Lagullas Cape, South Africa, 34 31 S. 19 57 Lebida, Tripoli
14 14 Loango R., West Africa.... 4 40 S. 11 12
! Lopez Cape, West Africa
8 40 Louis (St.) Fort, West Africa 16 IN. 16 Massowah, Abyssinia
15 36 1 9
33 E Matafou Cape, Algeria
3 14 Mellila, Morocco.
2 58W Mesurada Cape, West Africa 6 19 N
10 49 Mesurata Cape, Tripoli.
15 10 E. Mirik Cape, West Africa
32 W. Yogadore I., Morocco
1 9 44 Monasteer, Tunis
10 52 E. Morgan Cape, South Africa 32 42 S. 28 19 Natal Cape, South Africa.... 29 53
30 57 Negro Cape, West Africa... 15 41
11 53 Non Cape, Morocco
28 41N. 11 15 W. Nunez R. West Africa
14 42 Oliphant R., N. West Africa.. 31 41 S.
18 10 E. Oran Castle, Algeria
0 38 W. Palmas Cape, West Africa 4 24
7 46 Paul's (St.) Cape, West Africa 5 45
0 52 E. Portendik, West Africa... 18 19
16 2 W. Quillimane, East Africa
17 52 S. 36 56 E, Recif Cape, South Africa
25 36 Rovetta, Egypt
31 25 N. 30 28 Rnxo Cape, West Africa
16 51 W. Sallee, Morocco
6 46 Santa Cruz, Morocco..
9 42 Seven Capes, West Africa.. 24 41
15 1 Socotra I., East Africa ... 12 80
4 E. V Sookren. Tripoli.
19 18 Souakin, Nubia
37 26 Spartel Cape, Morocco
54W. Suez, Egypt
37 E. Syene, Egypt
32 55 Tangier, Morocco
5 54 Tetuan, Morocco
5 19 W. Three Points Cape, Guinea .. 4 45
4 Thebes (ruins), Egypt
82 39 E. Toubrouk, Tripoli
28 13 Verde Cape, West Africa.... 14 43
17 31 W Voltas Cupe, West Africa. 28
16 27 E. Whyda, West Africa..
6 19 N.
ON PHYSICS, OR NATURAL PHILOSOPHY.-No I.
OBJECT OF THE SCIENCE,
The object of physics, or natural philosophy, is the study of all 'in the air, and a great number of other bodies, to which the phenomena which material substances present, except those general appellation gas or aëriform fluid is applied. which relate to changes of internal composition; the latter the mobility of the molecules is still greater than in liquids; but come under the domain of chemistry. For example, selecting the special characteristic of gases is their unceasing tendency the metal iron as a subject of contemplation, we may study its to expand into a greater volume; a characteristic expressed by specific gravity, its degree of hardness, its property of weld- the term expansibility, and which will hereafter be demonstrated ing, of being drawn out into wire, and rolled or beaten into experimentally. The general term Auid is applied both to plates; all these phenomena depend upon the physical proper- liquids and to gases. The greater number of simple bodies, ties of the metal, and the study of such phenomena comes under and many compound ones, are capable of presenting themselves the domain of physics, or natural philosophy, sometimes called successively under the three forms of solid, liquid, and gaseous, mechanical philosophy. But iron is endowed with another according to the rariations of temperature to which they are set of qualities. It is capable of being dissolved in certain exposed. Of this successive change, water affords a well-known acids, and rendered invisible as iron, although its presence may example. Hereafter, when we farther advance into the regions be recognised by various tests. All this department of study of natural philosophy, it will be found that the three states of belongs to chemistry.
solid, liquid and gaseous, depend chiefly on variations of We have stated that matter (or material bodies) admits of molecular attraction and repulsion. being studied under two aspects : but what is matterIt is
On Physical Phenomena.-Every change which the state of a necessary to arrive at some understanding as to this qucstion body may undergo without involving alteration of composition before proceeding farther. Perhaps the best definition of mat- is a physical phenomenon. The falling of a body, the sound ter is comprehended in the expression, whatever falls or is produced by such falling, the freezing of water, all are physical capable of falling under the immediate cognisance of tho phenomena.
Lares and Physical Theories.—The term physical law is applied At this time, there are sixty-three known elementary or
to designate the constant relation which exists between any simple bodies ; that is to say, hodies out of which chemicai particular phenomenon and its cause. For example, in demons analysis has not succeeded in extracting more than one species atrating the fact that a given volume of gas becomes one-half, of matter. Nevertheless the number sixiy-three is by no one-third, one-fourth, &c., its original size, according as it is means to be regarded as the permanent representative of simple exposed to a degree of pressure, twice, three times, &c., we ilius. bodies. Possibly their number may hereafter be increased or trate the well-known physical law which is expressed by say. diminished, according as new sinple bodies may be discovered, ing that the volumes of gases are in an inverse ratio to the or those with which chemists are at present acquainted may pressures under which they exist. A physical theory is the colbe proved to be made up of simple constituents.
lection of laws relating to the same class of phenomena. Thus Bodies, Atoms, Molecules.-Every definite or limited amount we speak of the theory of light, the theory of electricity. of matter is termed a body or mass, and the properties of such Nevertheless this expression also applies, though in a more bodies or masses show that the matter of which they are com- restricted sense, to the explication of certain particular phenoa posed is not continuous, but is made up of elements, as it were, mena. In this latter sense, we speak of the theory of dew, the infinitely small; so small that they are incapable of physical theory of mirage, &c. or mechanical division, and not in actual contact, but in near Physical Agents.-as causes of the phenomena which bodies proximity; the distances between them being maintained by present, philosophers admit the existence of physical agents or reciprocal repulsions, known under the name of molecular natural forces, by the operation of which all matter is governed. forces. These minute elements of bodies are terned atoms, These agents are universal attraction, caloric or heat, light, and groups of atoms are termed molecules,-of which latter, a magnetism and tlectricity. Mere physical agents only manifest body or mass is only an aggregated collection.
themselves to us by their effects, their ultimate nature being Mass.-The rerm mass of a body is applied to the amount of completely unknown. In the present state of science, the matter which it contains. The absolute mass of a body cannot question still remains undetermined, whether the physical be determined, but its relative mass, considered with regard agents are to be regarded as properties inherent in matter, or to the miss of some other body taken as unity, can be readily whether they are in themselves subtle material bodies, impal: arrived at.
pable, pervading all nature, and the effects of which are the Physical Conditions or States in which Boilies exist.--These result of inovements impressed upon their mass. The latter states are three, each being well characterized and readily dis- hypothesis is that most generally admitted ; but being admit: tinguishable from the others. 1. The solid state. This condition ted, next follows the important question, Are these kinds of is manifested at ordinary temperatures by wood, stone, and
matter distinct amongst themselves, or are we to refer them to metals. It is characterized by an entire adherence of mole.
one and the same source:" This latter opinion appears to gain cules amongst themselves, so that they only admit of separa- ascendency in proportion as the boundaries of natural philosotion by the exercise of a certain degree of force, varying for phy, become expanded. Under the assumption that the phydifferent solids, and for the same under different circumstances. sical agents are subtle forms of matter, devoid of all appreci
: It is a direct consequence of this molecular adherence, that able weight when tested by balances of the highest sensibility, solid bodies retain their original forms. 2. T'he liquid state. they have been termed imponderable fluids ; hence arises the Of which we are furnished with examples in water, alcohol, distinction between ponderable matter, or matter properly and oils. The distinctive character of liquids is an adherence
so called, and imponderable matter, or imponderatle physical of 30 feeble a degree between their molecules, that the latter agents. slide upon and pass each other with extreme facility, in consequence of which it results that liquid bodies do not affect any form l
Different Kinds of Properties.-By the term properties of bodies containing vessel. 8. The gaseous state. Of this we have examples 1 or of matter is understood, the different methods by which they VOL. IV.
ON THE GENERAL PROPERTIES OF BODIES.
come within the spnere of our cognisance. These properties | diagram this correspondence occurs at the eighth division of are distinguished into general and special. The former are the vernier, counting from the point N. This coincidence those which belong to all bodies, of whatever kind and in what shows that the fraction to be measured is equal to eight-tenths. ever state they may be examined. The properties necessary to In other words, the divisions on the vernier being smaller than be considered at this time, are impenetrability, extension, divisi- than those on the fixed rale by one-tenth, it follows that if we bility, porosity, compressibility, elasticity, mobility and inertia. begin to count at the point of coincidence, and proceed in the Special properties are such as are observed in certain bodies, direction from right to left, each successive degree on the veror under certain physical conditions. Of this kind are solidity, nier falls in arrear of the corresponding degree on the fixed fluidity, tenacity, ductility, malleability, hardness, transparency, rule by one-tenth. Hence it follows, that in the case under colour, &c. For the present we shall only be concerned with consideration from the extremity n of the vernier, to the fourth the general properties of matter already mentioned; but it is division on the fixed rule, the intervening space is eight-tenths, proper to remark that impenetrability and extension, are not and we arrive at the final conclusion that the length of the so much to be regarded in the light of general properties of object M N to be measured, is equal to four of the divisions of A B matter as the essential attributes of matter itself, and which plus eight-tenths. Consequently if the divisions on the great or serve to define it. Furthermore we may here remark, that fixed rule are hundredths of inches the length of M N will be the terms divisibility, porosity, compressibility, and elasticity obtained almost exactly correct to one-thousandth of an inch. only apply to bodies regarded as made up of aggregated mole- Were it desired to be still more accurate, to obtain the length cules; they are inapplicable to atoms.
correct to the two or three thousandth part of an inch, it would Impenetrability. This is the property by virtue of which no then be necessary to divide a Binto hundredths of an inch, to cut two material elements can simultaneously occupy the same off the vernier rule until its length should be equal to nineteen point in space. This property, strictly speaking, only applies or twenty-nine divisions of the great rule, as the case might be,
In a great number of cases bodies appear to be and finally to divide the vernier into twenty or thirty equal parts. susceptible of penetration. For example, there exist certain But when such minute divisions as these have to be observed, alloys, of which the volume is less than the joint volume of the and the exact line of coincidence between the degrees of the vermetals entering into their composition. °Again, on mixing nier and the fixed rule accurately read off, the aid of a lens is water with oil of vitriol or with alcohol, the mixture contracts absolutely necessary. The vernier is not invariably a linear in volume. Such phenomena do not represent actual penetra- measure, as we have already described it; very frequently gra-: tion. The appearance is solely referable to the fact, that the duated circular arcs are supplied with' verniers, which are materials of which the acting bodies are composed are not in then usually engraved in such a manner that fractions of a actual contact. Certain intervals exist between them, and degree are read off in minutes and seconds. It may be proper these intervals are susceptible of being occupied by other here to remark that the vernier is also occasionally termed a matters, as will be demonstrated further on, when we come to nonius, and still more frequently in mathematical books of a treat of porosity.
past era, the norius vernier. It derives this name from Nunez, Extension. This is the property which every material body a Portuguese mathematician, who is considered by some to possesses of occupying a limited and definite portion of have been its inventor. This, however, is not the case. The space. A multiplicity of instruments has been constructed, instrument of Nunez, although designed for accomplishing a having for their object the measuring of space. Amongst similar purpose with the vernier, differed from it in some imthese the vernier and the micrometric screw
portant respects, and was far less efficient. important; we will therefore proceed to their consideration. The Micrometric Screw and Dividing Machines. The term microThe Vernier is so called from the name of its inventor, a metric is applied to that variety of screw employed for measur. French mathematician, who died in 1637. This instrument ing with precision the extension of length and breadth. It enters into the construction of numerous kinds of apparatus follows, from the very nature of a screw, that when it is well used in the study of the physical sciences, such, for example, as and accurately made, its pitch, or the interval exis ng between barometers, cathetometers, goniometers, &c. It is composed of any two successive threads, must be everywhere throughout its two engraved rules, the larger of which A B (fig. 1), is fixed and length the same. From this it follows, that if a screw be rotadivided into equal parts. The smaller rule is moveable, and to ted in a fixed nut, the former will advance a certain equal disthis in strict language the term vernier is alone applicable. I tance for each révolution, the rate of advance being proporTo graduate the vernier, the process is as follows. First of tionate to the degree of obliquity of the screw-thread. It fol. all it is cut to such a length as corresponds with nine divisions lows, moreover, that for every fraction of a turn, say Idoth, it of the large or fixed rule. It is then divided into ten equal only advances the izoth of the length of an interval between parts, from which arrangement it follows that every division aný two threads. Consequently if this interval be equal to a of the rule a d is smaller than a division of the rule A B by hundreth of an inch, and if at the handle extremity of the screw
there is attached a wheel or circle graduated into 400 divisions,
and tuming with the screw, then on turning the graduated Fig. 1.
wheel through only one division, the screw itself will be caused to advance to the extent of one 400th of an inch.
Dividing machines, as they are termed, depend on the application of this principle. Fig. 2 represents a dividing machine, intended for the division of straight lines. It is composed of a long screw, the thread of which ought to be perfectly regular, working through a fixed metallic plate, and its handle part attached to a fixed metallic circle A. Adjacent to this graduated wheel is attached a fixed index B-by means of which every fraction of a turn made by the wheel, and consequently the screw itself, may be easily discriminated. The nut
E, through wbich the screw plays, is attached to an iron rule The vernier being thus constructed as already described, let CD, which moves with the nut by a motion parallel to the axis u8 explain the manner of its application. Suppose it was desired of the screw. It is upon this rule which is fixed the object to measure the length of an object M N. We place it as repre- mn intended to be divided. Lastly, the table is supplied with sented in the figure.upon the great rule, the long axis of which two brass grooves perpendicular to DC, and upon which moves corresponds with that of the body to be measured, and we the slide-rest K, armed with the steel graver o. find that its length equals four units plus a certain frac- The machine being arranged according to the description tion. To value the amount of this fraction is the object of just given, two different cases may present themselves. Either the vernier. This is accomplished by sliding the vernier the rule m n has to be divided into equal parts of a determinate along the length of the fixed rule, until the end of the vernier length--for example, four hundredths of an inch-or it may corresponds with the end m n of the object to be measured. have to be graduated into a given number of equal parts. Under This adjustment being made, we next seek for the point of the first conditions, the course of the screw, or its length from coincidence between the divisions of the two rules, “In the thread to thread, being equal to one hundredth of an inch, the
operator turns the circle A through one-fourth of an entire revo- substance in an apartment the air of which is frequently lution, engraves a mark on the rule, then turns the wheel through renewed. another fourth of a revolution, engraves another mark, and so Another example of the extreme divisibility of matter, even proceeds until the operation is completed. Under the second when organised, is furnished by the globules of the blood. conditions, let us suppose the division of the rule mn into Blood is made up of red globules, floating in a liquid termed eighty equal parts to be the problem for solution. The serum. In man, these globules are spheroidal, and their diaoperator now commences by causing the screw to turn in meter only amounts to about the .0003tb part of
an inch. the direction from right to left, as relates to our diagram, Nevertheless, the particle of blood capable of being taken up. until the extremity m exactly coincides with the point of the on the point of a needle contains nearly 1,000,000 of such graver; then reversing the direction of rotation, and causing globules. But, what is more wonderful still, certain animals, the wheel to move from left to right, in relation to the diagram exist so amazingly small, that they can only be seen by the aid until the other extremity n of the rule corresponds with the of a microscope of high power. They move about as large point of the graver. The operator counts the number of turns, animals do; they are nourished; they possess organs; how
and the value of the fraction of a turn, if such exist, gone immeasurably small must those particles be of which sucha through by the graduated wheel in causing the rule cd to animals are composed ! advance from one extremity of the object mn to the other. The divisibility of any kind of matter having been pushed Then, dividing the total number of revolutions by 80, the so far that its particles are altogether imperceptible, even by quotient indicates the space along which the screw E must the aid of the most powerful microscope, experiments can advance for each both of in n. It only now remains to engrave no longer determine whether such matter be finitely or a mark on mn at the cessation of each partial revolution of infinitely divisible. Nevertheless, the stability of chemical the wheel.
properties belonging to each kind of matter, the invariability
of relation subsisting between the weights of combining eleDivisibility. This is the property which all bodies possessments, and other important considerations, point to of being susceptible of division into distinct parts. Numerous belief in a finite limit to material divisibility. Circumstances examples might be cited illustrative of the extreme divisibility of this kind have led philosophers to assume that bodies are
Thus one grain of musk is sufficient to evolve constituted of material elements not susceptible of division, during many years the peculiar odorous particles of that and to which, therefore, the term atoms is applied.
LESSONS ON CHEMISTRY.No. II.
latter is by far the more convenient plan of the two. I have TAKING up the subject at the point where we left off in our
not assumed the student to possess a cork-borer, but I will last lesson, the reader will remember that he must perform
describe the instrument, so that it may be made or procured at certain operations on certain corks. He must then adapt these such as is employed for the ferrules of fishers' rods, of equal size
once if convenient. It merely consists of a piece of brass tube, corks so treated, one to a four-ounce phial, another to a Florence flask, in such a manner that two instruments may be saw-edge at one end. If a transverse hole be bored through
with the hole to be bored, and sharpened by filing to a rough formed as represented in the diagram annexed.
the brass tube towards the other end, all the better: the conFig. 1,
The four-ounce bottel with its tobacco-pipe attachment, wil not be required just now, but we shall speedily want it, therefore let the arrangement be made at once. Now the treatment of the cork involves two separate processes, boring and external fitting, and the order in which these operations are performed is not immaterial. The boring operation must come trivance permitting the insertion of an iron wire as represented first. There are two methods of boring a cork; either by by a, thus attaching to the instrument a sort of gimlet handle, thrusting a pointed red-hot wire through it, and afterwards and conferring that kind of additional power which mechanics accurately enlarging the orifice by means of a rat's-tail file, or term for the sake of brevity "purchase," — with such an instrue by the use of a special instrugent termed a cork-borer. The ment as this, cork-boring is a very simple affair. A cork-bore,