The most useful invention of Franklin was what came to be known as the Franklin stove. With modifications, it is still in use, and the essay written on it by Franklin, entitled _An Account of the New-invented Pennsylvanian Fireplaces_, is one of the best illustrations of the capacity of his scientific genius to adapt itself to the hardest and barest offices that human comfort and convenience could impose upon it with a nicety and accuracy of trained insight and touch worthy of the cleverest journeyman, a command of scientific principles to be expected only of a professional student, and a gift of clear, lively expression which reminds us of the remark of Stella that Dean Swift could write agreeably even about a broomstick. The principle upon which the Franklin stove was constructed was that of making the heat from its open fireplace, after first ascending to its top, descend in such a manner at its back, before passing off into the chimney, as to diffuse by radiation through the room, in which it stood, a large part of its warmth. The essay enumerates the different methods of heating rooms then in use: the great, open, smoky chimney-place, that the unremitting labor of one man could scarce keep supplied with fuel, and that gave out little more heat for human warmth than a fire outdoors; this chimney-place reduced to a smaller size with jambs, and free, to a great extent from the reproach of smokiness, yet, with its contraction setting up strong currents of whistling and howling air, which reminded Franklin of the Spanish proverb, "If the Wind blows on you thro' a Hole, Make your Will, and take Care of your Soul";