The system of house numbering for the city of Philadelphia changed between the years 1856 and 1857 through the Ordinance of 1856, thus affecting house numbers along Market Street (Moak 11). Prior to the change, house numbers originated at both the Delaware and Schuylkill Rivers and extended towards the center of the city. The number assigned to a given house was determined by the number of buildings that stood between it and the river. In the case of Taylor's image, the house numbers originated at the Delaware and were 256 and 258. After the change in numbering, 256 became 726 and 258 became 728. This change created more uniformly numbered blocks within the city. Similarly, Market Street was known as High Street through the early nineteenth century. This website looks at buildings on the 700s block (the section of Market Street between 7th and 8th Streets). The below map marks the location of 726 and 728 Market Street in Philadelphia.
Moak, Jefferson M. "Architectural Research in Philadelphia: A Guide to the Resources Available throughout Philadelphia." Philadelphia: The Athenaeum of Philadelphia, 2002.
Map image taken from: http://maps.google.com/maps?sc=1&hl=en&output=html&q=728+Market+Street%2C+Philadelphia&btnG=Search&zoom=2
Last revised on 3 November 2005, MG Feedback