Complex sentence: Two years later he went to Harrow School as mathematical tutor, but the step proved unfortunate one, as the school was at its lowest ebb, and Colenso not only had few pupils, but lost most of his property in a fire.
Split into simpler sentences: Two years later he went to Harrow School as mathematical tutor, but the step proved an unfortunate one. The school was at its lowest ebb, and Colenso not only had few pupils, but lost most of his property in a fire.