Leaving aside the degradation of an alliance with a nameless man, and the possible fact that his property, in default of heirs male, might pass into such a one's power, he had sense to comprehend Heathcliff's disposition: to know that, though his exterior was altered, his mind was unchangeable and unchanged. 
Leaving aside the degradation of an alliance with a nameless man, he understood Heathcliff's character. He knew that, though Heathcliff's exterior was altered, his mind was unchanged. 