Page:Popular Science Monthly Volume 89.djvu/458

 444

��Popular Science Monthly

��Controlling Temperature and Humidity at the Same Time AX AI'I'ARATIS for automatically ±\ controlling the temperature and hu- midity of one or more spaces or rooms consists of a thermostat for determining the temperature and a hygrometer for determining the humidity, both instru- ments being electricalh' connected with a regulating mech- anism. The ther- mostat consists of an ordinary mer- curial thermometer having metallic contacts fused in its tube at pre- determined points to form contact with the mercury colunui.

One of the con- tact points is at the maximum heat- point, fixed at sevent>' degrees, and the other is at the minimum heat- point, which is tixed at sixty-five degrees.

When the mercury touches either of these contact points a circuit is closed and the temperature of the room is regulated accordingly. The principle invoKcd is of the simplest and its adoption ought to do much toward hel|)ing the weather man i)lease a limi- ted public.

The h\grometer consists of a flat heli- cal, or spiral, body composed of a highly hydroscopic substance which assumes various shapes and more or less expands according to the amount of humidity absorbed. The helical i)ody winds tigiiter or unwinds as the humidity fluctuates, and registers its moNcments b\' a dial swinging o\'er an index. Wiien the dial touches contact points on the index an electric circuit is thereby completed which either increases or diminishes the humi(lit\'.

In practice both of these controlling devices are connected to admit heated or cooled air to the room or space. With a rising temperature and increasing humidity circuits are dosed which actu- ate other apparatus which in turn operate to admit cooler and drier lir.

���Thermostat and Hygrometer Electrically Connected with Regulating System

��Electric Substitute for the Old- Fashioned Latchkey

ACOWllNTKNTand etticient device for unlocking any door fitted with a spring lock is shown in the accompany- ing sketch. A fairly stiff spring A, is connected by a flexible wire cord to the knob B. The cord is also fastened to a le\cr C. which is pivoted at D and is released by a mag- netic trigger E, made from the ar- mature and magnet of an old electric bell.

When the circuit is completed by means of a secret contact de\'ice out- side the door, the magnet F pulls down the armature which releases the trigger and allows the spring to open the lock. If there are metal numbers on theoutsideof the door thc\' may be used for the secret con- tact, if desired. If there are no numbers on thedoor,a small contact board ma>- be constructed by driving about lO brass- headed tacks into a thin piece of wood to make connections. Then however dark the night there will be no trouble opening the door. — Wilbir Seipel.

���Essentials in the Arrangement for Unlock- ing Door Without u Key

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