Very dangerous errors arise from statistical returns and insurance tables of the mean chances of life made up from gross returns of the mortality prevalent amongst large classes, who differ widely in their circumstances. Thus we find, on inquiry into the sanitary condition of the population of different districts, that the average chances of life of the people of one class in one street will be 15 years, and of another class in a street immediately adjacent, 60 years. In one district of the same town I find, on the examination of the registries, the mortality only 1 out of every 57 of the population; and in another district 1 out of every 28 dies annually. A return of the average or the mean of the chances of life, or the proportions of death in either instance, would and does lead to very dangerous errors, and amongst others to serious misapprehensions as to the condition of the inferior districts, and to false inferences as to the proper rates of insurance. With the view of arriving at some estimate of the comparative extent of the operation of the chief causes of sickness and mortality proved to be prevalent, amidst the different classes of society, in the towns where the sanitary inquiries have been made; I have obtained the following returns from the clerks of the several unions acting as superintendent registrars. These returns have, as far as practicable, been corrected by particular local inquiry, and are submitted as the best approximations that can readily be obtained. In all districts, and especially in the manufacturing districts, there is some migration of labourers which would, for the obtainment of perfect accuracy as to the chances of life in particular localities, have rendered necessary an examination of every individual case enumerated. This extent of labour has been considered unnecessary. In the returns from single towns, the numbers of deaths of persons of the first class are too small not to be affected by accidental disturbances, but when large numbers of the like class are taken, the uniform operation of the like circumstances are shown in the like results. It is at present a general defect of the important head of information, “the occupation of the deceased,” that the deaths of masters are not carefully distinguished from the deaths of journeymen. So far as this error prevails, it will tend to raise the apparent chances of life amongst the labouring classes. In some instances the occupations of the deceased, or of the parents of the deceased, in the case of children, are not described in the registries. With these and possibly with other defects that may have escaped notice, these returns will be received as corroborative of the reports of the medical officers and physicians who have attended and observed many of the individual cases themselves, though not enumerated by them. Had the mortality prevalent amongst workpeople of particular trades and their families