MESSRS. EDITORS:I have been told by a gentleman, who claims to have demonstrated it by experience, that a steam boiler covered with a casing of pure copper, the latter resting upon the rivet heads, thus leaving an an- splice between the casing and the boiler, will furnish a given amount of power from 20 per cent less fuel than the same boiler worked in a precisely similar manner, biit having a casing of iron, 0r any other metal, put on exactly like the copper. Though he is perfectly satisfied as to the results, he docs not pretend to explain the causes which produce this saving, but thinks it is due to some electrical influence. The copper, he says, must be perfectly pure, and the air space is also absolutely necessary. If there be such results obtained from such means, there must be good reasons for it, and it is of great i mportance that the matter be understood. If, by the light of science, you can satisfactorily explain this matter, and will communicate your ideas on the subj ect to me, either through the columns of your excellent paper Of by letter, you will greatly oblige. SAMUEL COMFORT, JR. Morrisville, Pa., Dec. 1, 1860. [We distrust the correctness of the account of this experiment; there are so few people competent to try an experiment thoroughly and give a perfectly correct description of it. 'Vas the coal carefully weighed and the amount of water which was evaporated carefully measured, when other substances than copper were employed under the same circumstances? There is great loss of heat by radiation from steam boilers, but wood, felt or plaster, we should suppose, would be better material for a jacket than copper, as they are slower conductors of heat. The air space is an excellent thing in a j acket.