In the last number of “Appleton's Mechanics Magazine,” there is an article from Capt. Ericsson on his Hot Air Engines. From the exciting advertisements published abont this article, as being something wonderfully great, we thought before we read it, that some acute and able reasoning, worthy of an answer, would be presented. But instead of this we have been disappointed. We advise every reflecting practical engineer to read it for himself, to be convinced ; that it is nothing but a batch of nonsence. We quote the following extract: I have repeatedly stated that the yielding of the wrought-iron heaters has prevented ull pressure being carried, and I have so re-)orted to Government. Strange to say, those who have written on the subject appear not :o comprehend the importance of this tact, nor its true bearing on the question. They all conlound the caloric engine with the team engine. In the latter, when reduced iressure is carried, the consumption of fuel is reduced in an equal proportionnot so in the caloric engine. The principal source of heat >eing the regenerator, neither speed nor pres-ure exercises any material influence on the juantity of fuel consumed. I must here em-ihatically record the fact, that the quantity of uel consumed in turning the wheels at the dock, at 4J turns per minute, differed very ittle from the quantity consumed under way, making 9 turns a minute. The reason is obvious ; the losses by radiation, and the heat passed off through the chimney, c, remain constant, whilst the capability of the regene-nerator changes with the speed, density of air, and temperature. By increasing these the power of the instrument increases in equal proportion; the more heat it receives in a given time, the more it gives back." Capt. Ericsson has also stated that his wrought iron heaters would not yield. Those who have written on their yielding have comprehended the difficulties, if not the importance of the same, and the owners of the Ericsson now feel it. It is not true that the hot air engine (caloric engine is a wrong name) has been confounded with the steam engine, and it is not true that reduced pressure in a steam engine reduces the consumption ot fuel. If he had said that high pressure steam used expansively, reduced the quantity of fuel he would have been correct. If the regenerator is the principal source of heat, why in the name of common sense does he use any fuel at all. It seems that the fuel his engine consumes is a sequent of his regenerator, and by this logic it is not the heal produced by combustion which moves his engine, but his regeneratorsoTie packages oi wire gauze. The " regenerator " ofthe hot ail engine is a humbug; it seems to humbug Capt. Ericsson and all the groundlings who believe that a certain quantity of heat can produce repeated effects upon innumerable quantities of mattera perpetual motion idea of the most absurd character.