728 Chestnut Street, Philadelphia, PA: William Y. McAllister c1867. Broadside, approximately 10 x 12 inches. Margins apparently trimmed top and bottom edges with no apparent loss. When purchased, this item was in a frame (provided if desired to the purchaser). Folded, creased, short closed tear to the bottom edge. Grey paper printed in black. Good. 
Willliam Y. McAllister appears in McElroy's Philadelphia directory (1865) at 728 Chestnut Street in Philadelphia. Catalogues from the firm are known from 1865 and 1867 (Romaine) as well as 1872, 1873, 1881, and 1919 (Davis and Dreyfuss). The firm was established in 1783 by John McAllister, Sr. and passed through many incarnations until W.Y. McAllister took over in 1865. Bracegirdle notes that the firm was at 728 Chestnut from circa 1860-1870. A circa 1882 William Y. McAllister catalog notes that McAllister & Bro was the immediate predecessor to the firm (1853-1865) and that W.Y. McAllister was active from 1865 "to date."
Since this broadside is undated, we spent some time reviewing the firm's catalogues from different timeframes, attempting to compare woodcuts. The best matches are to the 1867 Optical and Philosophical Instruments catalogue. The Zentmayer Grand American Microscope, the pocket magnifier, nose spectacle, Holmes' Spectroscope, and Revolving Stereoscope in the broadside all match the cuts in that catalogue (complete with woodblock damage). While true that cuts were re-used for many years (the pocket magnifier as one example appears into the 1880s complete with break in the block), it fits the time period nicely, and we feel comfortable with the general dating of this broadside. The Zentmayer Grand Microscope was only sold until circa 1876 providing the latest possible date.
In our experience advertising broadsides from this period in America are rare, and doubly so with this kind of illustration. No copies found in OCLC, nor have we seen any in the marketplace other than this example. A very nice item.
Ref: Romaine, A Guide to American Trade Catalogs 1744-1900 ; Davis and Dreyfuss, The Finest Instruments ever Made; Bracegirdle, Notes on Modern Microscope Manufacturers.