Sentence:  ... the influence of the minister's week-day attentions, first in creating, and afterwards in keeping up among the people of his parish their habit of Sabbath attendance. So indispensable in towns is the connexion between these two things, that were seat-rents let down at this moment to two shillings <WSD>overhead</WSD>, or even annihilated, so as to throw open the whole of the church room at accessible prices to the lowest of the people, we shall greatly mistake the result if we look for a great and visible increase of attendance "per saltum" on the part of the parish families. 
Meaning of the word marked with <WSD> tags:  Per head; for each individual.