Perhaps America’s finest violinist, Principal Guest Conductor Joshua Bell shows his astonishing range in this two-hour European tour: Mendelssohn’s surging Hebrides Overture finds Bell leading from the concertmaster seat; then he stands in the solo spotlight for the Spanish symphony that is (wink, wink) all about the violin; finally Bell takes the conductor’s podium for Mendelssohn’s ebullient “Italian” Symphony, full of sun-splashed melodies.