On page 221, this volume, we published some very useful remarks regarding spontaneous combustion, and described a simple apparatus invented by Dr. Hay, Admiralty Chemist at Portsmouth, Eng., for detecting an increase of heat in the holds of ships and in close rooms. In answer to the information there presented, we have received a letter from Henry D. Fiah, of Milford, Mass., in which he describes an apparatus similar in principle, but somewhat different in construction from that of Dr. Hay, for accomplishing the same objects and which he invented in October, 1856. We would recommend Mr. Fish to devote more attention than he has yet done, to the general introduction of his invention, as the object designed to be accomplished by it is a good one.