Scarcely a winter passes but one or more deaths are recorded from the products of combustion given off from various forms of water heaters used in bath rooms; scarcely a cookery class is given, with gas stoves, that one or more ladies do not have to leave suffering from an intense headache, and often in an almost fainting condition. And the same cause which brings about these extreme cases, on a smaller scale causes such physical discomfort to many delicately organized persons that a large class exist who absolutely and resolutely decline to have gas as an illuminant or fuel in any of their living rooms; and if the use of gas, more especially as fuel, is to be extended, and if gas is to hold its own in the future against such rivals as the electric light, then those interested in gas and gas stoves must face the problem, and by improving the methods of burning and using gas do away with the present serious drawbacks which exist to its use. The feeling has gradually been gaining ground in the public mind that, when atmospheric burners and other devices for burning coal gas are employed for heating purposes, certain deleterious products of incomplete combustion find their way into the air, and that this takes place to a considerable extent is shown by the facts brought forward in a paper read by Mr. William Thomson before the last meeting of the British Association. Mr. Thomson attempted to separate and determine the quantity of carbon monoxide and hydrocarbons present in the flue gases from various forms of gas stoves and burners, but, like every other observer who has attempted to solve this most difficult problem, he found it so beset with difficulties that he had to abandon it, and contented himself with determining the total amounts of carbon and hydrogen escaping in an unburned condition, experiments which showed that the combustion of gas in stoves for heating purposes is much more incomplete than one had been in the habit of supposing, but his experiments give no clew as to whether the incompletely burned matter consisted of such deleterious gases as carbon monoxide and acetylene, or comparatively harmless gases, such as marsh gas and hydrogen. After considerable work upon the subject, I have succeeded in doing this by a very delicate process of analysis, and I now wish to lay some of my results before you. If a cold substance, metal or non-metal, be placed in a flame, whether it be luminous or non-luminous, it will be observed that there is a clear space, in which no combustion is taking place, formed round the cool surface, and that as the body gets heated so this space gets less and less until, when the substance is at the same temperature as the flame itself, there is contact between the two. Moreover, when a luminous flame is employed in this experiment the space still exists between the cool body and the flame, but you also notice that the luminosity is decreased over a still larger area although the flame exists.