We must next combine the above enormously unfavourable chance, which we will call _a_, with the other chances of not guessing correctly beforehand the surrounding conditions under which _a_ was calculated. These latter are divisible into _b_ and _c_; the chance _b_ is that of not guessing correctly the general course of the ridges adjacent to each square, and _c_ that of not guessing rightly the number of ridges that enter and issue from the square. The chance _b_ has already been discussed, with the result that it might be taken as 1 to 20 for two-thirds of all the patterns. It would be higher for the remainder, and very high indeed for some few of them, but as it is advisable always to underestimate, it may be taken as 1 to 20; or, to obtain the convenience of dealing only with values of 2 multiplied into itself, the still lower ratio of 1 to 2{4}, that is as 1 to 16. As to the remaining chance _c_ with which _a_ and _b_ have to be compounded, namely, that of guessing aright the number of ridges that enter and leave each side of a particular square, I can offer no careful observations. The number of the ridges would for the most part vary between five and seven, and those in the different squares are certainly not quite independent of one another. We have already arrived at such large figures that it is surplusage to heap up more of them, therefore, let us say, as a mere nominal sum much below the real figure, that the chance against guessing each and every one of these data correctly is as 1 to 250, or say 1 to 2{8} (= 256). The result is, that the chance of lineations, constructed by the imagination according to strictly natural forms, which shall be found to resemble those of a single finger print in all their minutiae, is less than 1 to 2{24} x 2{4} x 2{8}, or 1 to 2{36}, or 1 to about sixty-four thousand millions. The inference is, that as the number of the human race is reckoned at about sixteen thousand millions, it is a smaller chance than 1 to 4 that the print of a _single_ finger of any given person would be exactly like that of the same finger of any other member of the human race. When two fingers of each of the two persons are compared, and found to have the same minutiae, the improbability of 1 to 2{36} becomes squared, and reaches a figure altogether beyond the range of the imagination; when three fingers, it is cubed, and so on.