tend that endeavour, and the actual re-union, constitute thecurious appearances called ELECTRICAL and GALVANIC. I must not attempt to carry you through these experimental scenes, because the apparatus will teach you more in an hour, than you could learn by reading in a week, and Dr. -, the geography master, sometimes indulges you in this way; but I must put you on your guard against the vulgar error, that there is, properly speaking, any electrical or galvanic fluid.

The appearances can be produced wherever there is air, composed of oxygen and nitrogen, as in electricity; or whenever nitrous acid (that is the same principles as in air) are put between plates of different metals, having different reactions; therefore the introduction of a special fluid is gratuitous. It was feasible enough before it was discovered that the air contained two principles, whose separation and reunion were sufficient to produce the phenomena; but it is monstrous to foist such a barbarism on the world in the present state of our knowledge.

Air is accounted 850 times lighter than rain water, and 2500 times lighter than glass; but I doubt whether its weight is any just and proper test of the number of atoms which it contains. Weight is a test of fixed bodies, but not of bodies whose essential characteristic is motion, and in motions contrary or lateral to the direction of the force of weight. I suspect that every space filled with gas is as full as gold, but the solidity is rendered insensible by the perfect fluidity and mobility of its parts.

From what I have said of the construction of air, you may infer its powers of expansion, compression, and elasticity. These, of course, are governed by the excitement, or by the size of the orbit, which the atoms by greater or less motions are excited to perform.

So much for the air of your school-room; and hereafter you will perceive that you constantly live

and move among wonders of the highest order. I hope I have not been prolix, tedious, unintelligible or uninteresting.

LETTER XL.

Light and Colours.

MY ESTEEMED Children,

Notwithstanding the seeming close of our aerial discussions in my last, there is one other subject, even lighter than air; I mean the glorious means by which your eyes are enabled to convey to your understandings the contents of these pages.

How is this effected? The pages do not touch the eye, and yet by some miraculous means the eye feels what is printed. The ancients imagined that something proceeded from the eye itself to the objectthe philosophers of the last two centuries believed that rays of light proceeded from the luminous body like sand or grape shot, and in their numerous reflections, reached objects first, and then the eyewhile it is more recently taught, in connexion with the chemical theory of combustion above described, that light consists of the propulsive excitement of the atoms, which fill every space, the different sizes producing different colours, and the affection of the whole, white light.

Sound, it is said, is an affection in mass, and light is an affection of atoms in trains not by undulations, but by propulsion from atom to atom. Transparent bodies, as glass, it is alleged, contain the atoms affected, and hence are seen through; and opake bodies do not contain them, or a sufficient proportion of them. The difficulty of conceiving that such atoms, as assumed rays of light, penetrate so

lid diaphanous bodies, and travel as is required 12 millions of miles in a minute, is removed by the new theory, because by it the propulsions, from atom to atom, are merely required to extend through every 12 millions of miles in a minute, each atom travelling, perhaps, not more than the millioneth part of an inch.

The explosion and collision of the hydrogen and carbon evolved by a combustible, and the crossing of the condensed oxygen, in the sphere which constitutes the film or surface of the flame, is considered as the competent cause of the excitement among the similar atoms which fill every space. It is, indeed, conceived, that the prismatic spectrum is merely a mechanical decomposition of the atoms affected, which are the mere identical atoms comprising atmospheric air.

The refraction or turning aside which the action of light undergoes, at the surface of diaphanous bodies, when it falls obliquely, owing to the light within the body being parallel to the surface, is the foundation of several delightful instruments by which the angle under which objects are seen by the eye, can be indefinitely enlarged. These are the TELESCOPE for distant objects, and the MICROSCOPE for near ones. Distant objects cannot be seen distinctly, merely, because the angle under which the parts appear are too small to be discerned, hence an image is created by the object glass of a telescope, and this image is viewed by an eye glass very close; and therefore the object itself appears magnified. The same purpose is effected by the microscope; for, with the naked eye, no object can be seen distinctly, within 6 or 8 inches; but by creating an image with one glass, and viewing the image very closely, by means of an eye glass, we magnify to any extent. In a word, the telescope and microscope are among the most glorious applications of art to nature, and open a noble field for the gratification of your curiosity. The telescope en

ables you to enlarge the angle under which the planets are seen, to discern the spots in their discs, and to number their invisible satellites; while the microscope enables you to view diminutive nature, and see perfect insects, hundreds of whom might dance on the point of a needle!

The science of light and colours also teaches us the true cause of the rainbow, and proves that it is the necessary effect of the double refraction and single reflection of drops of rain, when viewed in a determinate angle; and that another angle gives us a reversed bow from two reflections and two refractions, discoveries for which we are indebted to the genius of Descartes.

The PRISM which analizes light was a discovery of Grimaldi, and it shews us that a ray of white light is divisible into the seven colours of the rainbow, red, orange, yellow, green, blue, purple, and violet, the quantities or breadth of which correspond with the measures of the notes in the diatonic scale, and the coincidence seems to prove that light and sound are connected with the elementary proportions of atmospheric air.

In fine, the atmospheric air, yea, the very air which you breathe, and are so familiar with, is, in all its manifold qualities, one of the most useful and surprising things in nature. It is at once the source of animal life and its power, of sound, of light, and of various chemical agencies which operate on vegetables and minerals. It creates, by its separation, lightning and thunder, it holds clouds in suspension, it distils vapours, and precipitates rain, and it is in other respects a permanent source of comforts, blessings, and wonders.

LETTER XLI.

Dancing and School Balls.

MY ESTEEMED Children,

But while you are thinking of nature in her depths and heights, you must not forget the graces of your own persons. The dancing master after all is an important personage in every female seminary. I was always fond of his day, for it led you into healthful exercise, and seemed an employment so congenial to your minds and youthful spirits.

As the best practical results of this art are graceful attitudes and a good carriage of the person in walking, I have always been friendly to the daily use of the reclining board, and to the practice of promenading before the master. The mere arts of dancing follow of course, and you proceed in due progression from your steps to the sociable country dance, the graceful minuet, the lively quadrille, and the fashionable waltz. Figure dances are not only less useful, but they create a theatrical air which I never could approve.

As the public ball is the governesses's grand gala, I have often observed that too much is sacrificed to its effect. A month is commonly lost for the ostentatious display of a single evening. It ought not to be so, and I never permitted it. The dancing master ought through the whole year to be looking forward to his ball, and not derange every thing that he may fetch up his lost time.

To me, I confess, that my annual ball has always afforded the highest gratification, and it would have mortified me if the performance of my pupils on that occasion had not drawn forth the applause of all my judicious friends. I naturally expected all ages to exert themselves for my sake as well as their own