it touches the hottest part, and then ascends to pass into the house. Thus the air leaving the stove is much hotter than the smoke, it being about 200° Fah., while the smoke is about 120° Fah. This is the reverse of the condition usually experienced in air-heating apparatus. There the air and the smoke pass away in parallel channels, moving in the same direction. The smoke must, therefore, on leaving, be always hotter than the air it has warmed. In the stove here shown, the air and the smoke move in opposite directions. The stove requires charging with coke once only during 24 hours. It burns at a uniform rate during the whole time, the rate of combustion being regulated by a small slide which limits the admission of air. A drawing of this stove is shown as one that has been found convenient and economical, not as being the only suitable one. The principle urged for adoption is that of admitting to the centre of the house, or to the separate rooms, a liberal supply of warm filtered air, in addition to the usual open fires. For my part I use gas fires as being clean and economical, and we cook by gas, so that in my house no coke smoke is made, and we contribute no impurity to the atmosphere beyond carbonic acid, the sulphurous acid due to the sulphur of the coke. This is, however, less than was in the original coal. If all would conduct their house-warming on this plan our towns would light up as with the smile of sunshine, and our fogs when they come would pass harmless and unstained as a country mist. XIX. A Set of New Ring-off Instruments for Telephone Exchanges, &c. By D. SINCLAIR, Engineer, National Telephone Company. [Read before the Society, 16th November, 1887.] BEFORE describing the new indicator which is before you, it will be necessary for me to explain how such an indicator is required in Telephone Exchange work. As you are aware, it is the function of an Exchange to join, as required, any two of the wires which form the Exchange. Each wire in the Exchange passes through an ordinary electro-magnet as an indicator, and in some of the older systems the two lines wishing connection were joined, having both indicators in circuit. In the later and better-arranged Exchanges the two indicators are cut out, and the connecting wire has an indicator in its circuit; thus, only one, instead of two indicators, is in circuit while the subscribers are in communication-an arrangement which improves the speaking very much. In Telephone Exchange work it is found that when a subscriber is finished with a conversation, there has been, up to the present, no proper way of apprising the Exchange when he is finished, unless, indeed, in some towns where a separate wire is erected to each office for that purpose. It often occurs in practice that a subscriber wishes to make a series of calls as quickly after each other as possible, so that it is important that the exchange be got in each case immediately, and, at the same time, that the party who has been finished with should not be further troubled; and it is with this end in view that the instrument before you has been designed. The main features in the arrangement are-1st. That when two subscribers are joined together they can ring and speak to each other without making a signal of any kind in the Exchange. 2nd. Either of the subscribers so connected can cease to ring each other and has power to signal the Exchange, at the same time connecting his line automatically on to the operator's telephone, so that immediate attention is secured at all times. Any one |