Complex sentence: No particular apportionment method was used during the period 1850-1890, but from 1870 through 1910 the increasing membership of the House was calculated in such a way as to insure that no state lost a seat due to shifts in apportionment population.
Split into simpler sentences: No particular apportionment method was used during the period 1850-1890. But from 1870 through 1910 the increasing membership of the House was calculated in such a way as to insure that no state lost a seat due to shifts in apportionment population.