412. Acts done off the premises.

An act may be a breach of the covenant for quiet enjoyment even though it is done off the premises. Even at the time when actual physical interference with the demised premises was considered to be an essential element of any breach of the covenant1, an act done off the premises could be a breach if it caused physical interference with the demised premises (as, for example, where a lower stratum of minerals had been demised, and the landlord worked the upper stratum so as to cause the roof of the lower stratum to fall in and the mine