tenth gram

length (Metric) Obsolete term for the 10^-10 multiple of the unit, e.g. tenth metre = 10^-10 m (the angstrom).    

Akin to the modern scheme for floating-point numbers, G. J. Stoney in the 1860s proposed citing the exponent of a power of ten, verbally, to any unit as a convenient means of expressing decimal multipliers.
[Stoney G. J. Phil. Mag. (GB) Vol. 36, 138 (1868)] He used an ordinal number before the word to indicate a negative power (e.g. tenth metre), the cardinal number after for positive powers, e.g. ‘gramme-eight’ = 10⁸ g. The qualifiers were usually hyphenated.