Interpolation

Interpolation, in mathematics, is a useful process of obtaining approximately a number corresponding to a given quantity when the two numbers corresponding to two other such quantities are known. Thus, if the average height of a person 15 years old be known, and also that of a person 16 years old, it is a simple matter to calculate approximately the average height for an age of 154; years. The one assumption in this case is that the growth during the year is uniform. On this one assumption much interpolation is effected in mathematics, such as the calculation of the cosine (q.v.) of an angle of 23° .16' 5" when the cosines of 23° 16' and of 23° 17' are known; or the calculation of the logarithm (q.v.) of the number 62174 when that of 62170 and 62180 are known. By graphical methods the process may be extended considerably, even when the variation of the one quantity is not proportionate.