I have noticed with much interest the progress of Capt. Ericsson's" Hot-Air Engines" In an article copied by you from " Appleton's Mechanic's Magazine," in the Scientific American of the 18th ult., Capt. Ericsson alludes to the turning of the wheels of the " F.r-icsson," at the dock, 4J times per minute, and compares this with the revolutions when under way, at nine turns. I was in the city of New York at the time the Ericsson was fastened at the dock in Williamsburgh, and making these great turns of "4 times per minute," and had the curiosity to go over and witness the performance. I was not allowed to go on board, and had to make my examinations at a distance—but I made an important discovery, which I believe has not been made public, and that was, that all the buckets but one, in the water at a time, had been removed from the wheel, and this seemed to be a very narrow one—hence the reason of her ability to make even 4J turns, I made inquiry of the guard (who, by-the-by, informed me " I could not go on board even if I were Capt. Ericsson's own brother,") who gave as a reason for those off the buckets, " that the engine was too strong to put them all on at once, for fear ot breaking all to pieces." Some of the papers in your city were verv free to give the performance of the wheels at the dock, but, as I thought at the time, overlooked the little item that most of the buckets had been removed, and that those which were on were very narrow—if there had been none on the wheel I think the revolutions might have been increased. I wish to say that, in my opinion, you have done yourself and your paper much credit by an exposure of the defects ot the Hot-Air Engine. A. G. Chicago, 111., 1853.