taste, and none the less so because he laboured generously to make music the property of the people, thus concludes:"Let any one sing the above scales one after the other (four varieties of the so-called "minor scale"), and assuredly he will not be long in discovering which of the four is the most agreeable and natural, and most in the character of the minor tonality (key). It is evident that the scales with leading notes (NE), instead of being pleasing, are disagreeable to the ear, and impracticable to the voice. The absence of the leading (note (NE) on the contrary often gives to the melody something majestic and solemn. The Gregorian chant, so remarkable for melodious beauties, affords many proofs of this, and also the popular melodies of different countries, especially those of Ireland and Scotland, so much admired by the greatest musicians." Surely here is example and testimony enough to prove these noteswhether good or bad-at least non-essential and arbitrary. One question yet remains. Should not the scale on which minor tunes are framed be still treated as a distinct one, and something more than the common scale used in a peculiar manner? To which we answer-Yes, if it is distinct; but, if otherwise, why multiply difficulties and conceal the truth? But it clearly is not, in any particular, distinct. First, in reference to the "character or musical effect of the notes-the most important particular of all-the notes of the so-called minor scale correspond precisely with those of the common one (reckoning from LAH to LAH'.) Not a single note of the common scale changes its character when used in a minor tune. LAH is still the sorrowful, TE the piercing, FAH the awe-inspiring note, &c., as before. Next, in reference to the exact intervals between the notes-they are precisely the same as those of the common scale (from LAH to LAH1) with only this peculiarity, that the graver (flatter) position of the "variable note " RAY is ordinarily used in tunes of this character, whereas it is only occasionally used in other tunes. Premising that from DOH to DOH is commonly called by musicians a major key (beginning with a major, or greater, third, DOH ME), and that a minor key beginning on a note in the position of our LAH would be called its relative minor, let us quote the following testimonies to the last point. Colonel Thompson says-"The change to the relative (or, as it would more properly be called, the synonymous) minor reduces itself to avoiding the acute second of the old key (r) and using only the grave (r)." (See "Westminster Review," April, 1832). Dr. Crotch says "Some authors make it" (the first note of the principal minor key) "the same as the note LAH of the relative major key, viz., ▲ in the key of c, a minor tone" (smaller tone-of eight degrees) "above a (SOH). In that case all the natural notes excepting D (RAY) correspond with those of the major key of c." (See Crotch's "Elements"-Tuning, &c.) Turning to his illustrative plates, we find the scale of minor tunes requiring the smaller tone (eight degrees) between DOH RAY, and the larger tone (nine degrees) between RAY ME, while other tunes usually require a larger tone between DOH RAY and a smaller one between RAY ME. In fact the variable note assumes its grave position. But it sometimes does the same in the common scale. Is this, then, a peculiarity sufficient to establish a new scale? More over, is it not natural to suppose that the common scale, which is found to be essentially the musical scale of all nations, must hold a peculiar accordance with the ear and the sympathies of the human race? and is it not proper, therefore, to consider this as the one scale, and everything else that cannot establish a distinct and independent character as but a modification or a peculiar use of it? It is certain that great detriment must be done to the mind of our pupils, and great hindrance given to their progress, if we first cause them to study and practise our theory, of a new and self-contradictory minor scale, and then leave them to discover that, in music itself, instead of the artificial difficulties they have so laboriously mastered, there is only to be found the common scale, so used as to produce a peculiar effect and the merely occasional, non-essential, introduction of a new note! [We were present, in October last, at several choral performances of pupils who were taught to sing on the method developed in these lessons, some of which were attended by more than 3,000 people. We aw a choir of children who sang music at first sight, a thing quite new The "Tonic Solfa Association " numbered 2,000 pupils in Lonon alone last year, and the meetings referred to were the means of o ginating at once three new classes of about 200 pupils each. We may claim, for the POPULAR EDUCATOR, the credit of giving a cosmopolitan influence to these valuable efforts.]-ED.

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Sometimes in the course of a tune the music takes the "minor" character, introducing the new note NE, and returns again to the ordinary use of fi the common scale. Occasionally, too, the music passes into the minor of the soH KEY, making a new note, a tonule below ME, which (to distinguish it from NE of the original key) we call NU; and, not unfrequently, it enters the "minor" of the FAH KEY, originating another note, a tonule below RAY (r'), which we call NI. The modula-ni-1 tor at the side will illustrate these changes.

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Another "transition" into what is called the "minor of the same tonic" (DOH becoming LAH), is more proper to "tempered" musical instruments than to music itself or the unaided voice. You may treat it as transition into the key of ME flat, or, retaining the syllables of the original key, the new notes may be treated as chromatic. Thus you will have the oddlysounding notes мow, Low, and Tow, as any one may perceive by drawing the two keys side by side, and bearing in mind the difference between the tonule and the chromatic part-tone. Our pupils will now be able to ransack the stores of classical music, and to take their "part" in fireside glees, at their pleasure. They will be very largely, and, we hope, very long, rewarded for all the patience and painstaking which we have demanded of them.

ON PHYSICS OR NATURAL PHILOSOPHY. No. XIX.

(Continued from page 261.)

Fig. 79.

THE ELASTIC FORCE OF GASES. Experiments of Boyle. The principle that the elastic force of air increases in proportion to its density, was first proved by Boyle in 1660, in the following manner :-He took a uniform tube ABC, fig. 79, closed at c and open at A, and bent upwards so that the part CN was parallel to the part AM. Mercury was poured in at the open branch ▲ until the level in both branches of the tube stood at M and N respectively, and the air in the closed branch CN was of the same density as the external air in the sured and found to be 12 inches; the pressure branch AM. The distance ON was then meain both branches was equal to 30 inches of mercury, being that of the atmospheric air; and the height of the mercury in the longer branch AM above the level of that in the shorter branch was 0. More mercury was poured in at A, until the distance C N was diminished to 10 inches, and the mercury stood in the longer branch 6 inches above that level; the pressure in both branches was now equal to the atmospheric pressure, 30 inches of mercury, and 6 all; more mercury was again poured in at A, inches of mercury additional, or 36 inches in until the distance CN was diminished to 8 inches, and the mercury stood in the longer branch 15 inches above that level; the pressure in both branches being now equal to the atmospheric pressure and 15 inches additional, or 45 inches in all. The experiment was repeated again and again, and the results tabulated as

82.

The Manometer.-The name manometer (from the Greek, raritymeasure) is generally applied to instruments employed in measuring the tension of gases or vapours when it is greater than the pressure of the atmosphere. There are various kinds, as the freeair manometer, the compressed-air manometer, and the metallic manometer. In these different kinds, the unit of measure which is employed is the atmospheric pressure, when the barometer stands at 30 inches. Now, we have seen that this pressure on a square inch is 14 lbs.; consequently, if we say that a gas has a tension of two or three atmospheres, we mean, that it acts on the sides of the vessel which contains it with a pressure of twice or thrice the weight of 144 lbs. per square inch.

Free-air Manometer.-This manometer is composed of a strong glass tube BD, fig. 82, about 5 yards long, and a cistern D, made of iron, containing the mercury in which the tube is immersed. This tube is cemented to the cistern and fixed on a board, along side of which is placed another tube a c, made of iron, and about 5 yards long; by means of this tube the pressure of the gas or of the vapour is transmitted to the mercury in the cistern. As manometers of this kind are most frequently used in cases where vapour of high temperature, or steam, would soften the cement which is employed to fix the glass tube to the cistern, the tube A c is filled with water; and it is by this means that the pressure of the vapour is transmitted to the mercury.

In order to graduate the manometer, the orifice A is allowed to communicate with the atmosphere, and at the level where

1 is marked, signifying one atmosphere; then, proceeding from this point by 30 inches at a time, the figures 2, 3, 4, 5, and 6, which indicate the number of atmospheres, are marked, because a column of mercury of the height of 30 inches represents the pressure of the atmo sphere. Then the intervals from 1 to 2, 2 to 3, &c., are divided into ten equal parts, which give the tenth parts of an atmosphere. If the tube a be now put in communication, for example, with a steam boiler, the mercury will rise in the tube BD to a height which measures the tension of the steam. In the figure, the manometer is shown as marking 4 atmospheres, which are represented by 3 times the height of 30 inches, besides the atmospheric pressure at the top of the column. This kind of manometer is only used for pressures which do not exceed 5 or 6 atmospheres. Beyond this point it would be necessary to make the tube so long that it would be easily broken. In this case, recourse must be had to such a construction as that explained in the next paragraph.

Compressed-air Manometer. This manometer, founded on the principle of Mariotte's law, is composed of a strong glass tube closed at its upper extremity and filled with dry air. This tube is immersed in a cistern partly filled with mercury, to which it is cemented. The cistern, by means of a side tube ▲, fig. 83, is put in communication with a close vessel, which contains the gas or vapour whose elastic force is to be ascertained. As to the graduation of this manometer, the quantity of air contained in the tube is such, that I when the orifice A communicates with the atmosphere, the level of the mercury is the same in the tube and in the cistern. At this level, therefore, 1 is marked on the board to which the tube is attached. In continuing the graduation, it is necessary to observe that the pressure which is transmitted through the tube increasing, the mercury rises in the tube until its weight, added to the tension of the compressed air, balances the exterior pressure. If, therefore, we mark 2 atmospheres in the middle of the tube, we shall commit an error; for, when the volume of air in the tube is reduced to one-half, its tension, by the law of Mariotte, is that of two atmospheres; and, therefore, when increased by the weight of the column of mercury which is elevated in the tube, it represents a pressure greater than two atmospheres. The number 2 must not therefore be marked in the middle of the tube, but a little lower, and at such a height that the elastic force of the compressed air, added to the weight of the column of mercury in the tube, shall be equal to two atmospheres. By such a calculation as this, the exact position of the figures 2, 3, 4, &c., on the scale of the manometer is determined. This instrument is not very accurate when the pressures are great; for the volume of air becoming less and less, the divisions of the scale approach too near to each other.

The inconvenience of both the preceding instruments has been attempted to be remedied by employing an apparatus of the following description, fig. 84, Nos. 1 and 2. This manometer, invented by M. Richard, and of which No. 1 is the front view, and No. 2 the side view, is of the free-air description, indicates very high pressures, and is of a very moderate height. It consists of a tube doubled several times on itself, so as to present a series of vertical branches connected with one another by bent knees; that is, the instrument presents a continued series of siphons in the same vertical plane, alternating up and down and having the same vertical branches. The columns of mercury are separated by columns of water, which occupy the upper bent knees and the upper half of the height

of the branches. The apparatus being completely filled with columns of mercury and water, if one of the extremities of the tube be put in communication with the vessel of gas or vapour whose tension is to be ascertained, the other extremity remaining open to the free-air, the excess of the pressure in the vessel over Fig. 83.

the columns of mercury. This correction will be made by multiplying the preceding product by the fraction, which represents the ratio of the excess of the density of mercury above that of water, to the density of mercury. The doubled tube is made of iron; the second vertical branch open to the air is mounted with a glass tube to show the extremity of the column of mercury; and the scale, which is made of brass, is graduated to atmospheres.

Metallic Manometer.-M. Bourdon, a mechanician of Paris, has recently invented a new manometer, represented in fig. 85

This instrument, which is wholly metallic and without mercury, is constructed on the following principle, discovered by the inventor; when a tube having flexible sides and a slightly flat tened or oval shape is wound up in the form of a spiral, in the direction of the less diameter, every interior pressure on the sides has a tendency to unwind the tube; and, on the contrary, exterior pressure has a tendency to wind it up.

According to this principle, the manometer of M. Bourdon is composed of a brass tube, about 24 feet long, having its sides thin and flexible. A section across the tube, represented at s on the left in the figure, is an ellipse whose greater axis is about of an inch, and smaller axis about of an inch. The extremity a, which is open, is fixed to a tube with a stop-cock d, for the purpose of putting the apparatus in communication with a steamboiler.

The extremity b is closed, and moveable like the rest of the tube. Now, when the stop-cock d is open, the pressure which is produced by the tension of the vapour on the interior sides of the tube causes it to unwind. The extremity b is then drawn from left to right, and with it an index e, attached to it, which indicates on a dial-plate the tension of the vapour in atmospheres. This dial-plate is previously graduated by means of a free-air manometer, by putting the apparatus in motion with compressed air. This manometer has the great advantage above the preced ing manometers, of being extremely portable and not easily broken. It is now in operation in the locomotives upon several railroads in France.

Metallic Barometer.-M. Bourdon is also the inventor of a metallic barometer founded on the same principle as his manometer. This apparatus, represented in fig. 86, is composed of a tube similar to that of the manometer, but shorter, hermetically closed, and fixed at its middle point; so that the vacuum having been made in it beforehand, whenever the atmospheric pressure diminishes, this tube unwinds itself in consequence of the principle above mentioned. The motion is thus communicated to an index which indicates the pressure of a dial-plate. As to the transmission of the motion, it is effected by means of two small wires b and a, which connect the extremities of the tubes with a lever fixed on the axis of the index. If the pressure increases instead of diminishing, the tube will close in upon itself, and there is a small spiral spring at c, which then brings back the index from right to left, under the dial-plate. This barometer is of small

1st. The mixture, which always takes place rapidly, is continuous and homogeneous, so that all the parts of the whole mass contain the same proportions of each gas.

2nd. The sides of the vessel where the mixture takes place being inextensible, and the temperature constant, the elastic force of the mixture is equal to the sum of the elastic forces of the gases contained in the mixture, when each is referred to the whole mass, according to the law of Mariotte.

The first law is a consequence of the extreme porosity and expansive force of gases. It was first proved by the French chemist Berthollet, by means of the apparatus shown in fig. 87,

Fig. 87.

which is composed of two glass globes, each furnished with a neck and stop-cock, and screwed to each other. The upper globe was! filled with hydrogen, of which the density is 0692, and the other globe with carbonic acid, of which the density is 1.529 or 22 times greater than the former. The apparatus was placed in the cellars of the Observatory at Paris, in order to keep them from being shaken, and from every variation of temperature. The stop-cocks being then opened, as in fig. 88, the carbonic acid in the lower globe B, notwithstanding its greater weight, passed partly into the upper globe A, and, at the end of a little time, it was observed that the two globes contained equal proportions of hydrogen and carbonic acid.

LESSONS IN CHEMISTRY.-No. XVIII.

Consideration of the Results of Combustion in Oxygen Gas.-The experiments performed in our last lesson require that we should now investigate the theory of combustion.

We have seen every instance of combustion which has hitherto come under our notice to have been the result, or at all events the concomitant, of the union of the combustible with oxygen as the supporter. In point of fact, almost all instances of combustion are the result of the powerful action of oxygen upon combustibles: not all, however, as was formerly supposed; hence the definition of combustion, formerly accepted, namely, "rapid union of a combustible with oxygen," is not strictly true. Chlorine, iodine, bromine, sulphur, and perhaps certain other elements, may in some cases take the place of oxygen as supporters of combustion. The only definition of combustion justified by known facts is, "rapid chemical action attended by the evolution of light and heat."

The result of the combustion of substances in oxygen gas may be an oxide, an acid, or an alkali, according to the nature of the combustible. The first and second we have generated in the course of our preceding experiments; the third we shall form hereafter.

Returning now to a consideration of the contents of the jars or bottles in which our various substances were deflagrated, let us begin with that vessel in which the iron was burned. You will observe, scattered all over its sides and base, various little globules of a material not unlike iron to look at. If you remove these globules from the vessel, you will find them to be heavy and hard; not unlike the original iron in appearance, but more dull. In reality, they are a compound of oxygen with iron, or, in other words, the oxide of iron, "the black oxide," as we may call it, by way of contradistinction to iron rust, or "red oxide" of that metal.