In order to form a correct estimate of the average mortality in any district, it is indispensable that one’s records should extend over many years. Thus only is it that fallacies can be avoided which arise from the alternate pressure and remittance of epidemic disease. The havoc effected by a periodical visitation of influenza, cholera, or plague, varies, in like manner as the ordinary death-rate varies, in different localities; and its variation contributes importantly to fix the healthiness or unhealthiness of such localities. But obviously, if we wish for practical purposes to calculate an annual rate of mortality, and to decide, in respect of any district, what are the chances of life for its population, we must distribute the peculiar mortality of the pestilence-period over those years which intervene between visitations of the pestilence. Hitherto, in respect of the City of London, I have the record of only two years; two years differing from one another in the proportion of 30 to 22, and the mean mortality deduced from that biennial period would be 26 per thousand per annum.[31] I am, of course, unable to tell you with certainty whether that ratio be the true average death-rate of the City; but I incline to believe that an average calculated from a longer period, with less abrupt fluctuations, would give a lower figure as the accurate one. [31] On account of corrections already adverted to, this mean death-rate should be reduced, probably to 25.2. In future years, so long as I may have the honour of reporting to the Commission, I purpose proceeding, step by step, to the construction of a cyclical average from the materials which will constantly be increasing; and I trust that many years may elapse before any approach shall again be made to the high death-rate with which the cycle commenced. It may be useful, for the sake of comparison, that I should remind your Hon. Court of some of the more important differences which prevail throughout the country, in regard to the local rates of mortality. The extreme rates recorded in the Registrar-General’s last publication, relating to the septennial period 1838-44, give 14 per thousand per annum as the lowest average, and 33½ as the highest average, for a population male and female in equal proportion. The low average belongs to a district in Northumberland, numbering 27-28,000 inhabitants; the high average is assigned to Liverpool. For the whole south-east division of England (comprising more than a million and a half of inhabitants) the death-rate is but 19; while in parts of the division it falls very considerably below this average. I have thrown these and some similar comparisons into a tabular form, which may perhaps be interesting to you.[32] [32] Vide page 84.