The "May Oatway" alarm has got round the first difficulty in a most ingenious manner by adapting the principle of the compensation methods already described in connection with watches.
The alarm consists of a steel rod of a section found to be most suitable for the purpose. To the side is attached by screws entering the rod near the ends a copper wire, which is long enough to sag slightly at its centre, from which depends a silver chain carrying a carbon contact-piece. A short distance below the carbon are the two terminals of the electric circuit which, when completed by the lowering of the carbon, gives the alarm. Now if there be a very gradual change of temperature the steel rod lengthens slowly, and so does the copper wire, so that the amount of sag remains practically what it was before. But in event of a fire the copper expands much more quickly than the steel, and sags until the carbon completes the circuit. The whole thing is beautifully simple, very durable, quite consistent, and reliable. As soon as the temperature diminishes, on the extinction of the fire, the alarm automatically returns to its normal position, ready for further work.
Now for the second function, that of giving the alarm in many places at once. The closed circuit does not itself directly cause bells to ring: it works a "relay," that is, a second and more powerful circuit. In fact, it is the counterpart of the engine driver, who does not himself make the locomotive move, but merely turns on the steam. An installation has been introduced in the Poplar Workhouse—to quote an instance. Were a fire to break out, one of the 276 detectors would soon set twenty-five bells in action, one in each officer's room. Similarly, in the Warehousemen's Orphanage at Cheadle Hulme, every dormitory would be aroused, and every officer, including the Principal in his house some distance away. Messrs. Arthur and Company, of Glasgow, have a warehouse fortified with 600 of these "nerve centres," all yoked to four position indicators, three of which actuate a "master" indicator connected with the central fire-station. There is no hole or corner in this huge establishment where the fire-demon could essay his fell work without being at once spied upon by a detector.
We may glance for a moment at the mechanism which sends an unmistakable message for help. At the brigade station there is a number of small tablets, each protected by a flap, on the outside of which is the word SAFE, on the inside FIRE. Normally the flap is closed. As soon as the circuit is completed, a magnet releases the flap, and a bell begins to ring. Now, it is possible that the circuit might be closed accidentally by contact somewhere between the premises it serves and the fire-station. So that the official on guard, seeing "J. Brown and Company" on the uncovered tablet, might despatch the engines to the place indicated on a wild-goose chase.
To prevent such false alarms the transmitter not only rings the station up, but automatically sends an unmistakable message. When a fire occurs an automatic printing machine is set in motion to despatch a cipher in the Morse code four times to the station. An accidental circuit could not do this; therefore, when the officer sees on the receiving tape the well-known cipher, he turns out his men with all speed.
On arriving at their destination the firemen receive valuable help from the "position indicator," which guides them to their work. On a special board is seen a row, or rows, of shutters similar to those already mentioned. Each row belongs to a floor; each unit of the row to a room. A glance suffices to tell that the trouble is, say, in the most southerly room of the second floor. No notice is therefore taken of smoke rolling out of other parts of the building, until the danger spot has been attacked.
That the firemen appreciate such an ally goes without saying. Every fire extinguished is a point to their credit. Also, the risks they run are greatly diminished, while the wear and tear of tackle is proportionately reduced. The fireman is noted for his courage and unflinching performance of duty. The discomforts of his profession are sometimes severe, and its dangers as certain as they are at times appalling. Therefore we welcome any mechanical method which at once shortens his work, lessens his peril, and protects property from damage.
Mr. Oatway draws special attention to the need for simultaneous warning on the premises and at the fire-station. "I remember," he says, "many cases, but perhaps no better illustration need be looked for than the case of a cotton mill in Lancashire about two years ago (1901). The fire was seen to start at a few minutes past seven; a fuse blew out, and sparked some cotton; but it looked such a simple job that the operatives elected to deal with it. At twenty minutes to eight it dawned upon somebody that the brigade had better be sent for, because the fire was getting away; and in due course they arrived; but the mill, already doomed, became a total loss. In every centre similar instances can be quoted. There is nothing in any automatic system to discourage individual effort. Inmates can put the fire out, if able; but in any case the brigade gets timely and definite notice, and if on their arrival they find the fire extinguished, as Chief Superintendent Thomas put it when we opened the Dingle Station after the fatal train-burning, 'So much the better, we shall get to our beds all the quicker.' This is the common-sense view of it. Helpers work none the less intelligently because they know the brigade is coming; and it is necessary to provide some automatic method of calling them, because you can never rely upon anybody who is unfamiliar with fire doing the right thing at the proper time."
Messrs. May and Oatway, who give their name to the alarm described above, first introduced their apparatus in New Zealand, from which country it has spread over the British Empire. The largest installation is at Messrs. Clark and Company's Anchor Mills, Paisley. The whole of the immense block of buildings, the greater part of which was previously protected by "sprinklers" only, is now electrically protected also; and connected up with the fire brigade, and through their station with the sleeping quarters of every fireman. Some figures will be interesting here. There are 119 miles of internal alarm circuits; 5 1 / 4 miles of underground cable between buildings; 19 automatic telegraphs; 21 automatic position indicators; 20 alarm gongs a foot in diameter.
Early in January, 1905, a fire broke out in these buildings during the dinner hour, when most of the works' firemen were at their midday meal. The alarm sounded simultaneously at the works' fire-station and at the firemen's houses, which are situated on the other side of the street from the mill. The firemen were on the spot immediately, and were enabled to subdue the flames, which had broken out in the building occupied as warehouse and office, before it had got a firm hold of the inflammable material, although not before one of the large stacks of finished thread was ablaze. The brigade, however, were soon masters of the situation, and the damage done was under £100. There is little doubt, had the alarm been left to the ordinary course, the building would have been totally destroyed.[15]