The initiatory efforts of Sower have a particular significance in the story of American type founding; for the tradition is that while engaged in the casting process of type making in the Germantown foundry, Justus Fox and Jacob Bay learned the more difficult mysteries of an art in which later they attained proficiency. Because of the link of continuous effort thus formed between Sower's initiation of the business in 1770 and the later cutting and casting of Roman letter by these artisans, there must be conceded to him the distinction of having begun in English America the industry of type manufacturing, regardless of whether or not his casting of German letter from imported matrices was as extensive as has been supposed.
Our knowledge of Fox and of Bay is derived largely from the _Additions to Thomas's History of Printing_, a body of tradition of uneven reliability transmitted to Isaiah Thomas by William McCulloch, a Philadelphia printer active in the early years of the century. Selections from the six communications of the period 1812-1814 in which this information was transmitted were incorporated by Thomas in the revision of his book upon which was based the second edition brought out by the American Antiquarian Society in 1874. Long afterward the series of letters was published as a whole in the _Proceedings_ of the Society for April 1921 under the title, _William McCulloch's Additions to Thomas's History of Printing_.
In these letters to Isaiah Thomas, McCulloch was recording his own memories and the accepted Philadelphia tradition. Because he was well advanced in years at the time of writing, one is not surprised to find that now and then he trips over the barrier that separates documented fact from hearsay and personal recollection. It is much to our comfort in the present instance, however, to learn that he possessed and made use of unusual opportunities to obtain correct information as to the craftsmen who are the subject of our interest. These facts which he records of Justus Fox, for example, he obtained from Emmanuel, the son and partner in type founding of that artisan, and in _Justus Fox, a German Printer of the Eighteenth Century_, Dr. Charles L. Nichols accepts his testimony as of general reliability. He was indebted to various relatives of Bay, among them a sister, "a plump lady of 68," for the account of him which is found in the pages of the _Additions_. It is possible to compare various items in McCulloch's sketches of these men with records unknown to him, but available to us, with results so little at variance that one is inclined to accord a high degree of credence to all that he wrote concerning their activities.