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55. From what has been said, (10, &c.) it appears that if bodies be impregnated with two systems of particles which are endued with forces attractive in their action on particles similar to themselves, but mutually repulsive of each other, the following results will ensue.

That a transverse vibratory motion of the one must, in general, be accompanied by a transverse vibratory motion of the other, (10) (34); that a translation is generally consequent on, and varying in intensity with, this vibratory motion (36). That when one fluid moves forward the other moves backward (10). By reference to those substances in which it would appear that the vibrations of the internal ether were considerable, the velocity of transmission of heat was found (by means of the hottest point of the spectrum) to be also considerable. And further, that when a body contained a large quantity of caloric, it uniformly (with one exception, and that not a striking one,) has been found to contain a proportionably small quantity of ether; results in which theory is confirmed by experiment.

SECTION IV.

Combination of Vibratory Motion with Motion of Translation when the Forces are repulsive.

56. IN the last Section we were occupied with the interpretation of the equations resulting from supposing the particles attractive, or, at least, the force on any one of the same denomination as would result from this hypothesis. It is possible to conceive that in nature the particles are so mixed and so varied in their properties as to allow the above supposition, at the same time that the total action produced on another system is of the opposite denomination. We ought then to examine the nature of the motion on each supposition separately, and, finally, to combine them.

57. I should be trespassing beyond the bounds of my subject, were I to proceed to the consideration of the modification which such an hypothesis introduces.

I shall therefore content myself with a few observations.

If we examine the equations of motion of the medium acted on by repulsive forces, we find them assume the form

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from which we conclude, as before, that there is a vibration in the direction of transmission, and that there is a transfer, the motion of any particle being in the plane of the front of a wave.

This seems to be connected with the fact of Electro-Magnetism, in which a current produces a force in a plane perpendicular to its direction. I said a force, but it will easily be conceived that if a system be put in motion, and some other body containing similar particles be within its sphere, the effect will be a repulsion in the direction of the motion, as a particle within the body will have a tendency to motion.

58. The conclusions at which we have arrived, as to the difference of motion in the two systems of fluids, seem also to bear upon this point; for, from our analysis, it appears that the motion of one fluid will be exactly the opposite of that of the other. The greatest difficulty that Electro-Magnetism presents, is the circumstance that each system acts always in one direction.

It is foreign to my present purpose to consider this point, but it seems probably connected with the circumstance that a flow of Galvanism necessarily commences from the source; whether that be the positive or negative, I am not prepared to say.

59. In conclusion I would observe, that nothing which I have advanced has the slightest tendency to invalidate the results to which M. Fourier and others have been led.

The equations which they obtain may be deduced from the principles of this method with the same facility as from their own. I regret that it is not in my power to multiply examples by which, not only the application of a process can be tried, but even the truth of the principles be tested. The relation between the sign of a small term in the expansion, when the coefficients are determined by observations of the places of the fixed lines in the spectrum, and the permeability of the substance to heat combined with the place of the hottest point in the spectrum, is of a kind that tends to strengthen our convictions in the truth of the principles when satisfactory; and, to help us to modify those principles when unsatisfactory: on which account, I cannot help expressing my regret that those Philosophers, who have so admirably shewn the intimate connexion between Heat and Light, should not have undertaken observations on substances such as to compare the gradations in the affection of the latter with

those of the former.

The nature of the investigation I have here attempted must plead my excuse for having been rather discursive. My object has been so to consider the constitution of the atmosphere, that one single hypothesis shall suffice as a key by which to proceed to the examination and explanation of the varied phenomena which present themselves to our notice. I do not presume to suppose that I have succeeded, but the necessity of keeping the different kinds of phenomena in as intimate connexion as possible, has induced me to offer the above to the notice of the Society.

ERRA TU M.

Is Part I, page 179, replace the seven lines from the bottom by the following:

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XI. On the Relative Quantities of Land and Water on the Surface of the Terraqueous Globe. By S. P. RIGAUD, A.M. Savilian Professor of Astronomy in the University of Oxford.

[Read Feb. 13, 1837.]

From the constitution of the Earth it is obvious that the greatest part of it is unfitted for the habitation of human beings. This, however, has been well accounted for. The fertility of the land depends upon the moisture of the atmosphere, which could not be furnished in sufficient supply, except from a wide expanse of waters and with mountains which may assist in its condensation. The oceans, therefore, bear a large proportion to the continents; but the relative distribution of them still remains a subject of great difficulty. The more accurately we study nature, the more clearly we see the operation of final causes, and, as a general truth, there can be no doubt that some beneficial objects are attained by the relative situation of those different portions of land, which rise above the level of the waters. Future investigations may lead to the discovery of them, and the best assistance, which can at present be given to the inquiry, must depend upon obtaining an accurate view of the facts. Even if we can as yet advance no further than physical phaenomena, it is well worth while to examine them with precision.

The irregular figures and sinuous outlines of the land are serious impediments to the common methods of measuring its extent. It has therefore been suggested, that by cutting out the delineations of it and weighing the several parts, an estimate might be made of its relative magnitude. Dr Halley, in 1693, published an account, which he had in this manner collected of the number of acres in each

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