"The problem... which specially belongs to the physicist is to investigate whether there is a sensible magnitude which is infinite. We must begin by distinguishing the various senses in which the term 'infinite' is used. 1) What is incapable of being gone through, because it is not in its nature to be gone through (the sense in which the voice is 'invisible'). 2) What admits of being gone through, the process however having no termination, or what scarcely admits of being gone through. 3) What naturally admits of being gone through, but is not actually gone through or does not actually reach an end. Further, everything that is infinite may be so in respect of addition or division or both."