Compare the number of legislators who started the term in 1875 and 2005.
started the term in 1875 refers to start LIKE '1875%'; started the term in 2005 refers to start LIKE '2005%'
SELECT SUM(CASE WHEN `current-terms`.start LIKE '2005%' THEN 1 ELSE 0 END) - ( SELECT SUM(CASE WHEN start LIKE '1875%' THEN 1 ELSE 0 END) FROM `historical-terms` ) FROM `current-terms`