MESSRS. EDITORS.—I cheerfully comply with your suggestion in regard to the Caloric Ship. I have much pleasure in assuring you that nothing whatever has occurred in working the machinery indicating the difficulties that can prevent the successful realization of this important enterprize. The only difficulty we have met with is that of the cylinder bottoms or heaters having proved too elastic and yielding to remain air-tight, or to admit of full pressure being carried. On the return of the ship from the South, two months ago it was deemed advisable to replace these heaters, which are made of boiler plate, by others of cast-iron, as that material admits of being made of any required thickness.— Only one foundry having been found willing to undertake the casting of these, requiring from six to eight months for their completion, we have been compelled to adopt a different plan; one, however, that will insure increased power and speed. As the modification which this involves calls lor a work of great magnitude, our friends will have to exercise, some little patience. Allow me, in connection with this remark, to remind you that it is only thirteen months since the keel of the Caloric Ship was laid, and that steamships of her class usually require eighteen months for completion. Mr. Collins, in building his ships, found nearly twice that time requisite. As the modification of a patented machine is not properly a subject for public discussion until completed, you will, I am sure, see the propriety of my not furnishing a statement of what is now being done to the machinery of the caloric ship ; as soon as the work is completed, the owners of the ship will be most happy again to invite the liberal press of New York to see the result of the second step in the development ot the great motor. I am, Sir, very respectfully, Your obedient servant, New York, May 20, 1853. J. ERICSSON. [This letter was addressed to the Commercial Advertiser. Our readers will see that Capt. Ericsson, confirms all we have predicted respecting the caloric engine. On the 11th of last January the Ericsson made her second trip down the Bay with the corps editorial aboard. On that occasion, as we have stated before, in answer to a question put by Alex. Jones, Esq., of this city, Mr. Ericsson made a contrary statement in respect to his heater bottoms, to that which he makes in the foregoing letter. It was understood by all present that his heater bottoms were to last four or five years. In the " N. Y. Tribune" of the 12th January, it says, " There is no danger either of fusion, cracking, or oxidizing, of the cylinder bottoms, all of which have been predicted by the sceptical—a cylinder bottom will last five years." So much for what the "Tribune" said. Victor Beaumont, a French engineer, published an article in the " Herald " at the same time, in which he used the following language :—" The bottom of the cylinders (heaters) is a convex surface, it is supposed they will be able to endure longer than four years, the average duration of boilers in the United States." On that celebrated occasion, the 11th of January, when the editorial corps in this city (as has been proven since, and as will be still further demonstrated yet) did no honor to the profession on board the Ericsson, the Committee consisting of Richard Grant White, Prof. Mapes, and Freeman Hunt, appointed to draft resolutions, penned the following one (the 4th of a series) which was adopted. " Resolved. That the pecular adaptability to sea vessels of the new motor presented to the world by Capt. Ericsson, is now fully established and it is likely to prove superior to steam for such purposes." By Capt. Ericsson's letter above, we now learn that his new motor, so far, has tailed to operate successtully, for if it did so operate, foolish, indeed, is he and those who have invested their money in it to go into such a vast and unnecessary expense, as " the modifi. cation which is now to be made in his engine, and which he calls "a work of great magnitude." v The caloric engine, Capt. E. tells us, is to be modified, and this modification is not a proper subject for discussion." These words are pregnant with meaning ; the inference to be drawn from them is that the trip of the Ericsson to Washington was " the beginning of the end." At some future time, we will have to present our readers with a full review of the whole case ; but we must bide our time.