Counting experiments have been tried on birds more frequently than on any other class of animal, and several species, notably ravens, rooks, and jackdaws, have solved this type of problem. This success may not be entirely by chance, for there is reason to believe that…

…of objects present is called counting. The numbers thus obtained are called the counting numbers or natural numbers (1, 2, 3, …). For an empty set, no object is present, and the count yields the number 0, which, appended to the natural numbers, produces what are known as the whole…

The concept of the atom is an ancient one; the Greek philosopher Democritus (c. 460–c. 370 bce) proposed a form of “atomism” that contained the essential features of the chemical atom later introduced by the British chemist John Dalton

…such as the system of counting by 20s, are clearly innovations, but this system is shared by English (“three score and ten”), French (quatre-vingts “80”), and Danish, in all of which it is also an innovation, as well as Basque, in which it appears to be old.

…theories is the concept of countability. If a certain number of particles is known to be present inside a certain space, that number will be found there later, unless some have escaped (in which case they could have been detected and counted) or turned into other particles (in which case…