Intensive magnitude or Degree is in its notion distinct from Extensive magnitude or the Quantum. It is therefore inadmissible to refuse, as many do, to recognise this distinction, and without scruple to identify the two forms of magnitude. They are so identified in physics, when difference of specific gravity is explained by saying, that a body, with a specific gravity twice that of another, contains within the same space twice as many material parts (or atoms) as the other. So with heat and light, if the various degrees of temperature and brilliancy were to be explained by the greater or less number of particles (or molecules) of heat and light. No doubt the physicists, who employ such a mode of explanation, usually excuse themselves, when they are remonstrated with on its untenableness, by saying that the expression is without prejudice to the confessedly unknowable essence of such phenomena, and employed merely for greater convenience. This greater convenience is meant to point to the easier application of the calculus: but it is hard to see why Intensive magnitudes, having, as they do, a definite numerical expression of their own, should not be as convenient for calculation as Extensive magnitudes. If convenience be all that is desired, surely it would be more convenient to banish calculation and thought altogether. A further point against the apology offered by the physicists is, that, to engage in explanations of this kind, is to overstep the sphere of perception and experience, and resort to the realm of metaphysics and of what at other times would be called idle or even pernicious speculation. It is certainly a fact of experience that, if one of two purses filled with shillings is twice as heavy as the other, the reason must be, that the one contains, say two hundred, and the other only one hundred shillings. These pieces of money we can see and feel with our senses: atoms, molecules, and the like, are on the contrary beyond the range of sensuous perception; and thought alone can decide whether they are admissible, and have a meaning. But (as already noticed in § 98, note) it is abstract understanding which stereotypes the factor of multeity (involved in the notion of Being-for-self) in the shape of atoms, and adopts it as an ultimate principle. It is the same abstract understanding which, in the present instance, at equal variance with unprejudiced perception and with real concrete thought, regards Extensive magnitude as the sole form of quantity, and, where Intensive magnitudes occur, does not recognise them in their own character, but makes a violent attempt by a wholly untenable hypothesis to reduce them to Extensive magnitudes.