For a period in the nineteenth and early-twentieth centuries, some authors followed Heaviside in the use of elastance and elastivity. Today, the reciprocal quantities capacitance and permittivity are almost universally preferred by electrical engineers. However, elastance does still see some usage by theoretical writers. A further consideration in Heaviside's choice of these terms was a wish to distinguish them from mechanical terms. Thus, he chose elastivity rather than elasticity. This avoids having to write electrical elasticity to disambiguate it from mechanical elasticity.