Another cause of the greater frequency of fires in New York and their more destructive nature is the greater density of population in that city.  The London Metropolitan Police District covers 690 square miles, extending 12 to 15 miles in every direction from Charing Cross, and contained in 1881 a population of 4,764,312; but what is generally known as London covers 122 square miles, containing, in 1881, 528,794 houses, and a population of 3,814,574, averaging 7.21 persons per house, 49 per acre, and 31,267 per square mile.  Now let us look at New York.  South of Fortieth Street between the Hudson and East Rivers, New York has an area of 3,905 acres, a fraction over six square miles, exclusive of piers, and contained, according to the census of 1880, a population of 813,076.  This gives 208 persons per acre.  The census of 1880 reports the total number of dwellings in New York at 73,684; total population, 1,206,299; average per dwelling, 16.37.  Selecting for comparison an area about equal from the fifteen most densely populated districts or parishes of London, of an aggregate area of 3,896 acres, and with a total population of 746,305, we obtain 191.5 persons per acre.  Thus briefly New York averaged 208 persons per acre, and 16.37 per dwelling; London, for the same area, 191.5 persons per acre, and 7.21 per house.  But this comparison is scarcely fair, as in London only the most populous and poorest districts are included, corresponding to the entirely tenement districts of New York, while in the latter city it includes the richest and most fashionable sections, as well as the poorest.  If tenement districts were taken alone, the population would be found much more dense, and New York proportionately much more densely populated.  Taking four of the most thickly populated of the London districts (East London, Strand, Old Street, St. Luke’s, St. Giles-in-the-Fields, and St. George, Bloomsbury), we find on a total area of 792 acres a population of 197,285, or an average of 249 persons per acre.  In four of the most densely populated wards of New York (10th, 11th, 13th, and 17th), we have on an area of 735 acres a population of 258,966, or 352 persons per acre.  This is 40 per cent. higher than in London, the districts being about the same size, each containing about 1-1/5 square miles.  Apart from the greater crowding which takes place in New York, and the different style of buildings, another very fertile cause of the spreading of fires is the freer use of wood in their construction.  It is asserted that in New York there is more than double the quantity of wood used in buildings per acre than in London.  From a house census undertaken in 1882 by the New York Fire Department, moreover, it appears that there were 106,885 buildings including sheds, of which 28,798 houses were built of wood or other inflammable materials, besides 3,803 wooden sheds, giving a total of 32,601 wooden buildings.