It was Warner’s opinion, however, that if it had originally been a Philadelphia and Reading engine, it was more likely to have been either the _Boston_ or the _J. E. Thayer_ of Eastwick and Harrison rather than a locomotive built by another firm, of which the Lowell-built _Conestoga_ of 1842 had been considered by some to be the chief possibility. At first glance the _No. 3_ appears much more modern than its actual age, but this is mainly because it has the 4-4-0 wheel arrangement with which people today are more familiar. The cab, not original, is of a design similar to that used on the _Pawnee_ class of engines first built at the Reading shops in 1852. Also not original are the headlight, the sandboxes, and the truck wheels. Sandboxes worked from the cab were not used in this country prior to 1846; the truck wheels, 30 inches in diameter, are of cast iron, manufactured by A. Whitney & Sons of Philadelphia, whose wheel foundry was established in 1846. The smokestack has obviously been altered, if not replaced entirely. The _No. 3_, now an anthracite-burning locomotive, is thought to have been originally a wood burner. The firebox is of the Bury type, which was in common use up to 1850. The four driving wheels of the _No. 3_ are 42½ inches in diameter, the extreme wheelbase is 178 inches, and the distance between the two driving axles is 55½ inches. The inclined cylinders are connected by long rods to the rear drivers. The exact cylinder bore, which had not been known for many years, was measured in October 1954 by representatives of the Reading Co. and found to be 12¾ inches. The stroke is 18 inches. The type of reversing mechanism designed by Andrew M. Eastwick in 1835 is thought to have been originally applied, and it is also thought that the original steam chests are still on the locomotive. The old valve gear has been replaced by a double-eccentric motion, the two eccentric rods being respectively attached to the top and bottom of a straight link. When the new motion was applied, the old reversing blocks were removed from the steam chests and discarded, the new valves being placed directly on the valve seats. This made it necessary to use only the lower stuffing boxes for the valve rods, and so the upper openings were permanently closed by suitable fittings. There are but two positions for the reverse lever, as was the case with the original valve gear, and the valves are always worked full stroke. The absence of definitive facts concerning the early history of the _No. 3_ is challenging, and it would add much to railroad history if in the near future the complete story could be developed as a result of further study of the locomotive itself, and of the written records.