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 



