The Wealth of Nations by Part 5 Chapter 2 Page 88

still continues to be so. Through the greater part of the kingdom this tax falls still more lightly upon the rent of houses than upon that of land. In some few districts only, which were originally rated high, and in which the rents of houses have fallen considerably, the land-tax of three or four shillings in the pound is said to amount to an equal proportion of the real rent of houses. Untenanted houses, though by law subject to the tax, are, in most districts, exempted from it by the favour of the assessors; and this exemption sometimes occasions some little variation in the rate of particular houses, though that of the district is always the same.

Improvements of rent, by new buildings, repairs, etc., go to the discharge of the district, which occasions still further variations in the rate of particular houses.