higher regions. It further appears to me that every particle of soft iron attracts indifferently both kinds of magnetic particles, but that magnetised iron attracts the one kind and repels the other, from a tendency to restore the equilibrium. Whether experiments will confirm these conjectures must remain, for some time, doubtful, but I do not conceive that the conclusions I have already come to in this paper will be at all invalidated by the result.

The most interesting practical application of the foregoing theory is to the deviations which take place in the compasses employed on board of ships in their navigation; and there can be no doubt, that the results deduced in such cases from this theory would be perfectly accurate, since the greatest care is invariably taken that no iron shall be in the immediate vicinity of the compass, and the disturbance, which it appears has sometimes proved of fatal consequence, arises wholly from distant large masses, necessarily distributed throughout the vessel. The situation of the centre of attraction of the whole of the iron contained in the ship might be found experimentally, from the deviations of the compass at particular places where the dip was known, and the deviations would thence be determined, on any particular bearing of the ship's head, in another part of the globe, provided the dip of the needle were also known at that place; but unfortunately this is a datum by no means easily obtained on board a ship, since the vessel must be perfectly at rest during the observation, and besides, this element would be liable to some error, the dipping needle being itself disturbed by the action of the iron on board. Should however any theory of the inclination of the needle be found to agree with all the observations made in different regions of the earth, as that given by M. Biot, founded principally on the

observations of M. Humboldt, agrees with those in certain regions near to the equator, the dip of the needle might then be found from the latitude and longitude of the place of observation, and the deviations of the needle could be determined, on every bearing of the ship's head, from the preceding theory. Another subject, but more of a philosophical nature, to which this theory may be applied, is the changes which have taken place in the variation and dip of the needle. On this I shall not at present enter, since the table of the variations and dip of the needle, which I have been able to procure, for any particular place, is very imperfect. I have however made some computations founded on this theory, and, in the absence of the requisite data, to be derived from accurate observations at distant dates, making certain assumptions, respecting the period of the changes and the alterations in the dip of the needle, find that the variations deduced from the theory coincide, within less than half a degree, with those observed in London, as far as I can judge from the table in my possession, during a period of two hundred years. I am not aware of the dip of the needle having been observed more carefully at any other place than in London, but should I be able to procure a tolerably correct table of the dip and variation of the needle observed at any place, for a long period of time, so as to have more certain data than in the computations I have already made, I shall resume the enquiry, and the result may form the subject of a future communication.

Royal Military Academy, Woolwich,

May 10, 1820.

IX. An Account of some Fossil remains of the Beaver,

found in Cambridgeshire.

BY JOHN OKES, Esq. OF CAMBRIDGE.

HONORARY MEMBER OF THE SOCIETY, MEMBER OF THE COLLEGE
OF SURGEONS, &c.

[Read March 6, 1820.]

FROM all that has been collected by naturalists relative to the abode and habits of the beaver, as well as its anatomical peculiarities, we may not only conclude that the fossil remains of that animal found in this and other countries, are of the same species, but also that the beaver has once been indigenous to Great Britain. In addition to the facts already published in support of this opinion, many of which have been detailed in the first number of the Edinburgh Philosophical Journal, I will relate the following account of some fossil remains found in this county, the only specimens, as it appears, that have been yet discovered in England. They consist of the left halves of two lower jaw-bones, which were dug up by a labourer two years ago about three miles south of Chatteris, in the bed of the Old West Water, formerly a considerable branch of communication between the Ouse and river Nen, but which, according to the traditions of the fen people, has

been choked up for more than two centuries*. These bones, the only remaining portions of four skulls, are nearly equal in size though not equally perfect, and like most other mineralized remains taken from a peat soil are stained a dark brown colour, arising perhaps from the great commixture of vegetable matter with the soil. The long and very powerful incisive tooth belonging to each halfjaw is perfect, and of the four grinding teeth proper to each in a complete state, the last only has been lost. It is from the singular structure of these teeth, that Cuvier has derived one of the distinguishing features of this tribe of gnawers (rongeurs); he says, "le caractere generique des molaires de castor, est d'avoir l'email de leur couronne replié de maniere de former trois lignes rentrantes du bord externe, et une seule de l'interne a la machoire superieure et precisément l'inverse a l'inferieure. Leur nombre est partout de quartre, dont la premiere seule est susceptible de changer." The more perfect of our fossils, is only defective in a part of the coronoid process, the other having lost both the coronoid and condyloid processes, as well as a great part of the incisive canal.

Besides these bones of the beaver, it appears from a communication, for which I am indebted to Mr. Girdlestone of Chatteris, that in a stratum of clay, about half a mile eastward of that town, has been found part of an elephant's skull, which the labourers broke to pieces, preserving only the two grinding teeth that were contained in it; and that near the same spot was dug up

* The accuracy of this tradition respecting the old West Water, is proved by the following extract from an Order of Council quoted in Dugdale's History of the Fens.

Anno 1617. 9 Maii. 15 JAC.- -“That the rivers of Wisbeche and all the branches of the Nene and West Water be clensed, and made in bredth and depth as much as by antient record they have been.”

It is important to shew the antiquity of the river from whose bed the fossils were removed, for by distinguishing it from those artificial and comparatively recent channels by which the fens have been drained, we refer its existence to a period, when the animal may with great probability be supposed to have been indigenous.