through the parish, the bill for the preceding year, makes an actual enumeration of the families, houses, and individuals. In the year 1776 the number of inhabitants was 7936, and, in the year 1785, 10522, so that in nine years there has been an addition of 2586 people. And, if we may trust the obfervation of our fenfes the increase has been, at leaft, equal, in most of the parishes to which the manufactory extends.

I find an article in the bill of mortality, for the parish of Eccles, in the year 1784, afcertaining the number of ex-parifhioners, buried there, in that year, which amounts to ninetyfive. From the fituation of the church, as diftant from every other parish but that of Manchester, I am convinced that, by far the greatest proportion of them come from hence. And as I have alfo no doubt, but there are greater numbers carried out to the different chapels of eafe and neighbouring parishes than are brought in from other townships and parishes, I believe I may ventureto affert that, the number of deaths, in Manchester and Salford, are greater than they appear to be from our own parish register. The burial grounds within the towns, are either fo crowded, or fo expenfive, as to deter many perfons from depofiting their deceased relations in them. Yet, even making every allowance of this kind, the great fuperiority of the births over the burials cannot be difputed. During the laft

fix years, though the latter have been unusually numerous, the registered births have exceeded the registered burials, by an average of 433, annually*.

Since this paper was read, the bills of mortality, for the years 1786 and 1787, have been published. In the former year, the registered births amounted to 2219, and the burials to 1282; fuperiority of births 937. In the latter, the births were 2256, and the burials 1761-fuperiority, 495. And as none of the diffenters are baptized, though many are buried, at the churches, the proportions of births to burials is ftill greater than is stated. Taking the year 1785 into the account fo as to form a period of three years; the average annual number of births, during that period, will be 2139, and that of the deaths, 1592. The former multiplied by 26.5 produces 56683, and the latter, by 30.5 produces 48556; the average of thefe numbers will be 52619, and if we allow fifty unregistered funerals and 150 births for the diffenters, and multiply and average these as above, we shall have 2745, which added to 52619, will prodace 55364, and may be received as nearly the number of inhabitants in Manchester and Salford at the beginning of the present year.

AUGUST 25, 1788.

CONJECTURES

CONJECTURES relative to the CAUSE of the INCREASE of WEIGHT acquired by fome HEATED BODIES, during cooling; by THOMAS HENRY, junior. Communicated by THOMAS HENRY,

F. R. S. &c.

READ MARCH 28, 1786.

MAN

ANY experiments have been made by different perfons, with a view to determine, whether the addition of actual heat to bodies does increase their weight. M. Buffon has afferted, that a ball of iron, weighing, when cold, 49lb. 110Z. increafed in weight, when made of a white heat, in the proportion of 19 grains to every pound. But, it is very probable, that, in this experiment, there was some fallacy, fince we find it directly contradictory to the refults both of the experiments made by Dr. Roebuck*, and of those made by Mr. Whitehurst. The first of these two Gentlemen found, that a cylinder of wrought iron, heated to a welding heat, at which time it weighed, in a very accurate balance, fifty-five pounds,

Phil. Tranf. vol. LXVI.

+ Ib.

gradually

gradually acquired, as it cooled, an increase of weight, fo that, at the end of twenty-two hours, it weighed fix penny weights, feventeen grains more, than it did when firft committed to the balance. This phænomenon, which, by fome has been adduced to prove, that heat is the principle of levity in bodies, Mr. Whitehurst has endeavoured to explain, by fuppofing, that the air, above the fcale being rarefied by the heated iron, the cold air below rushed up, and, ftriking against the bottom of the scale, not only prevented its defcent, but even buoyed it up. Something may perhaps be attributed to this caufe. But would not the circumambient air beneath the fcale be nearly as much rarefied as that above? And is it not probable, that the fuppofed force of this current of air, would be, in great measure, counteracted by the greater tendency a body has to defcend in a rarefied, than in a denfe medium? Is it not probable, likewife, that the end of the beam, to which the heated iron was appended, would by the fame heat which rarefied the air, be more expanded, and lengthened, owing to its nearer approximation to the fource from which the heat flowed, than the more diftant end of the beam? I would likewife obferve, that in the experiment of M. Buffon above quoted, and in one made by Dr. Roebuck on a fmaller fcale, the mafs, owing perhaps to the

joint action of the above causes, weighed more when hot, than when cold.

Having thus endeavoured to fhew, the infufficiency of the explanation given by Mr. Whitehurft, I will venture, with the greatest diffidence, to propofe the following query. May not the increase of weight, acquired by heated iron, and copper, during cooling, be ascribed to the calcination, and confequent abforption of air, continuing to proceed after the removal of the mafs of metal from the fire, the abforption of air in particular, in the firft ftages of the cooling, perhaps, with increased rapidity? In fupport of this conjecture, the following facts may be adduced. Firft; That fome metals, particularly copper, are found to calcine more rapidly, in a moderate degree of heat, than in one more intenfe. Secondly; That, the calces of fome metals, as that of lead, have been obferved to increase in weight by long expofure to the air, and that they now afford by proper treatment, more air, than could have been obtained from them, previous to fuch expofure. Thirdly; We fhall find by examining Dr. Roebuck's account of his experiments, that the weight continued to increafe long after the cause affigned by Mr. Whitehurst must have ceased to act. The cylinder, which was repeatedly

* Macquer's Inft. of Chemistry, vol. I.

weighed