BOOK V.
DEFINITIONS.
1. A less magnitude is said to be a part of a greater magnitude, when the less measures the greater ; that is, when the less is contained a certain number of times ex- actly in the greater.
2. A greater magnitude is said to be a multiple of a less, when the greater is measured by the less; that is, when the greater contains the less a certain number of times exactly.
3. Ratio is a mutual relation of two magnitudes of the same kind to one another in respect of quantity.
4. Magnitudes are said to have a ratio to one another, when the less can be multiplied so as to exceed the other.
5. The first of four magnitudes is said to have the same ratio to the second, that the third has to the fourth, when any equimltiples whatever of the first and the third being taken, and any equimultiples whatever of the second and the fourth, if the multiple of the first be less than that of the second, the multiple of the third is also less than that of the fourth, and if the multiple of the first be equal to that of the second, the multiple of the third is also equal to that of the fourth, and if the multiple of the first be greater than that of the second, the multiple of the third is also greater than that of the fourth.
6. Magnitudes which have the same ratio are called proportionals.
