captain South's estimate was taken from the poil-tax, in 1695, we have already observed that it must be extremely deficient, and far below the truth; and from the table formed upon the late returns of the registers of baptisms, burials, and marriages in this country, the population in England in 1700 does not appear to have been quite five millions and a half. By comparing captain South's estimate with the return of 1791, Mr. Newenham supposes the population of Ireland to have more than twice doubled in ninety-six years, while the increase in England is only supposed to be as 9 to 7.

By comparing, on the other hand, the return to the House of Lords, in 1731, with that in 1791, we find that the popu lation in Ireland only doubled in sixty years; and by the results of the Population Act, the increase in England, during the last century, has been as 10 to 6. It still, however, must be allowed, that there is an apparent disparity, the subordinate causes of which, in England, our author supposes to be the establishment of manufactures unfavourable to health, the Increase of luxury, and the consolidation of farms; but the great efficient causes he takes to be the less uniformly abundant supply of the sort of food on which the inferior classes of people have been accustomed to subsist, and the comparative infrequency of marriage. The latter circumstance he attributes to the operation of the Poor Laws, the tax on marriages, but chiefly to the characteristic difference in the modes of living. The labouring poor in Ireland, to induce them to enter into the marriage state, require only a mud cabin and a potatoe-garden. The wages of their labour they seldom receive in money, and think themselves in a highly thriving state when they can afford a pig or two, some poultry, a dog, and a cat, to help themselves, without ceremony, out of the same large dish, round which the family squat themselves to enjoy a hearty meal of milk and potatoes.

In the sixteenth section we have rather an interesting account of the numerical proportion of the Roman Catholics to the Protestants in Ireland. This proportion differs materially in different parts of the country. In many parishes the inhabitants are almost all Roman Catholics; in others the proportion is as high as 50 and 60 to 1; and in the three southern. provinces of Leinster, Munster, and Connaught, taken together, the proportion is at least 9 to 1. Upon the whole, it seems certain, that making allowance for the greater number of Protestants to be found in the northern counties, the proportion of Roman Catholics to Protestants throughout Ireland exceeds 4 to 1. It appears also, that the Roman Catholic religion has, in fact, gained ground upon the Protestant. We shall make no comment at present on this part of the subject, though the

following remarks of the author might give rise to much observation.

When a proscribed, or nearly tolerated religion greatly exceeds the established one, in point of numerical strength, the or dinary causes of the extension of the former will always be effectually aided by the concurrent operation of many others.

That the Roman Catholic religion, under its present circumstances, will continue to gain ground on the Protestant religion, in Ireland, is, I think, indisputable. The increasing wealth of the country, it is true, annually raises up a considerable number of individuals, from the middle classes of the community, consisting at present, in the three provinces before-mentioned, chiefly of Koman Catholics, to the higher ones, consisting almost wholly of Protestants. But we find instances of conversion among the wealthy Roman Catholics, notwithstanding their association with Protestants, extremely rare. They look to the attainment of much greater political weight by adhering to, than by forsaking the religion of their ancestors. By the former they expect to stand among the leaders of a most powerful party; by the latter, they perceive that they must rely on their talents and good fortune alone for future political distinction.

As for the lower orders of the Roman Catholics, not the slightest hope of converting them can now be entertained. Whatever ground the Roman Catholic has, in reality, gained upon the Protestant religion in Ireland, such ground, I have not the smallest doubt, will not merely be maintained, but enlarged, at least so long as the principal efficient causes of the extension of the former religion continue to operate.'

The concluding section is a species of Romance on the competency of Ireland to support a much greater population than it now contains; in which, after prophesying that in 1837 there will be found no less than 8,413,224 inhabitants, he proceeds with the utmost facility to the improvement of some millions of acres, leaving little uncultivated but what is barely necessary for lakes, rivers, and highways; and with the same ease and certainty raises above twelve millions of tons of potatoes, together with abundance of all other sorts of provisions, to afford sufficient and ample entertainment for his increasing multitudes. He at last winds up his speculations with the following peroration:

A due consideration of the various facts which have been brought into view in the foregoing pages, cannot, it is presumed, fail to impress every reader with the vast and increasing importance of Ireland in the political scale of the British empire: and to excite in every good, loyal, and patriotic man, the utmost solici tude for the continuance of internal tranquillity in that country, manifestly qualified to furnish, in the greatest abundance, the

means of sustaining the power of the United Kingdom amidst the momentous changes which Europe seems likely to undergo.

The recollection of recent events, accompanied by reflection on the nature and inveteracy of those principles of disunion, which have hitherto so frequently had the effects of blasting the growing prosperity of Ireland, and rendering it one of the most vulnerable parts of the British dominions, may create despondency in some. For my part, I think there are considerations which strongly tend to excite sensations of a very different nature.

Surely Irishmen, of all sects, have sufficiently experienced the diversified mischiefs of religious animosity; and must languish for its utter and final extinction. Surely Irishmen, of all parties, have had sufficient reason to lament the calamitous effects of internal feuds and commotions. Surely Irishmen have no longer to learn that dark, foul, and treasonous conspiracies, confederacies, and alliances, not only involve individual ruin, but induce political imbecility, national poverty, humiliation, and subjection; and that industry, civilization, internal tranquillity, and alacrity in maintaining the authority of the laws, while they must necessarily be productive of the happy effects of drawing over a large proportion of British capital, ingenuity, and experience, and eventually giving additional and lucrative employment to thousands, are the true and only means whereby Ireland can attain that enviable pre-eminence which nature has qualified her to enjoy. Surely Irishmen are prepared to admit that although the late political system of their country did undoubtedly supply the means of rendering it conspicuous amongst the nations of Europe, yet that, under an equitable and well-cemented union, the sister islands cannot fail to experience the highest possible commercial and political advantages, mutually enriching, strengthening, and aggrandizing each other. Surely Irishmen must derive some consolation from the thought of their country's having become, after ages of politi cal depression and turmoil, a prominent and most influential part of a vast empire, distinguished by an unprecedented combination of exalting circumstances; by great and increasing opulence, high martial renown, undisturbed internal repose, and perfect civil liberty, enjoyed by all ranks and descriptions of the community: an empire possessing the means of becoming irresistible; and much more likely to endure than any which has ever existed.

Surely Irishmen must perceive that while, on the one hand, it is demonstrably inconsistent with the real welfare of their country to urge any factious, frivolous, unfounded, or unnecessary claim; it is, on the other, no less so with that of England, to withhold any benefit which Ireland may acquire a right to enjoy. Surely Irishmen may find grounds for being persuaded that the statesmen of the United Kingdom, sensible of the vast real importance of Ireland, will ever be disposed to investigate promptly, patiently, and minutely the grievances and claims of that country; to redress the former, if real, and admit the latter, if well founded, and notified in the temperate, cautious, steady, and becoming manner

which accords with the spirit of the British constitution, and corresponds to the dictates of political wisdom."

As Englishmen, we surely and most cordially agree with our author in every sentiment dictated by a sincere regard for the general prosperity of the United Kingdom. We shall view, with the utmost pleasure, every improvement in the circumstances and conduct of Ireland which may entitle her to her due proportion of the glory and happiness of the empire at large, and shall at all times be happy to find Mr. Newenham attending more to limited practice than to extensive theory, in promoting these important and beneficial effects.

ART. VIII.— An experimental Inquiry into the Nature and Propagation of Heat. By John Leslie. 8vo. 145. 1804. Mawman.

IT is not our intention to enumerate, in a prefatory discussion, the many difficulties that embarrass the subject of heat: nor to attempt the statement or the refutation of the opinions, some whimsical, many wild and merely conjectural, that have been promulgated concerning it. The present author, wisely and modestly, announces his inquiry to be experimental: and with his experiments is our chief concern. It is our intention to state them in their order and connexion, so that they may of themselves indicate the inferences to be made, and suggest the classification of the facts that are established.

The fact of the reflection of heat by concave speculums has been long known; but no philosopher, previously to Mr. Leslie, we believe, has examined the difference of the intensity of the reflected heat, as arising from the difference of substance and surface in the heated body; nor the difference of the intensity of the reflected heat as dependent on the nature of the reflecting speculum. This examination forms the first part; and, in our opinion, the chief merit of the present volume.

Small accessions of heat are, it is known, conveniently and sensibly indicated by an air thermometer; and the common instrument, now in use, would, perhaps, have been adequate in all the leading experiments narrated in the first part, to the purposes rendered by Mr. Leslie's differential thermometer. This instrument consists of a glass tube bent into the form of an U, the tops of the syphon being surmounted with bulbs; the tube contains coloured liquor, which, it is clear, all other things equal, would stand at equal heights in each branch. If, however, the air in one bulb is more heated than the air in the other bulb, an increase of elasticity, or of expansive force,

takes place, and the coloured liquor is forced to ascend in the opposite branch above the ordinary level. This instrument is ingeniously contrived, and is properly called a differential thermometer, since it indicates the difference of the respective or absorbing powers of heat, which different substances possess, such substances being made to envelope, or to adhere to, the bulbs.

The apparatus of Mr. Leslie consisted of the differential thermometer, of concave reflectors, and of cubical canisters, made of metal, glass, &c. Suppose now two canisters, one of metal, the other of glass, placed similarly at equal distances, between two equal reflectors, in the foci of which are placed the bulbs of differential thermometers. According to our author, the effects from metal and glass are, a and a + b, (a = 12, b = 84 ±): nearly the sanie effects result, if the side opposed to the reflector be paper, or a thin coating of lamp-black. Hence a very remarkable, and to the generality of philosophic observers, an unlooked-for difference is manifest in one of the modes, by which vitreous and metallic substances disperse their heat.

Will any difference result if the focal ball of the thermometer be covered with tin foil? The effect on the thermo meter, from the blackened side of the canister, instead of being 90 degrees, is 20, and from the bright side of the canister only 24 degrees: hence, without the presumptuous propaga tion of any theory, it should seem that the receptive power as well as the propagative power of metal, is much less than that of glass or of paper. But if the receptive or absorbing powers are different in metal and glass, must not the reflecting powers be different? or, glass absorbing more heat than tin, less heat ought to be reflected on the focal ball from a glass reflector, than from a tin reflector. Experiment proves, that from a concave mirror the effect on the focal ball is very small and the same, when the back of the mirror is freed from the silvering, or is made rough by the attrition of emery; but, let the face of the mirror be covered with tin foil, then the effect is ten times that which is produced by the naked mirror.

The facts related in this chapter will be deemed at least very curious: and viewed all together, they are calculated, I think, to affect us with surprise. Nay, they are repugnant to our first notions, and might experience contradiction, if they were not so easily verified. We might admit, perhaps, without much hesitation, that blacking, and even paper, are, by their constitution, more receptive of heat than the bright surface of metal; but if this quality results from any particular affinity or superior attraction, how shall we conceive that those soft substances likewise discharge CRIT. REV. VOL. 4. April, 1805.

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