Page:Popular Mechanics 1928 01.pdf/9

 to check the water level in the reservoirs, he calls the number of the reservoir, the operator completes the connection, and the hell at the other end rings. The signal operates a relay that lifts the hook and starts a buzzer that sends back through the transmitter a signal to advise the caller that contact is established and also the desired information.

 

By using the blotter that has been applied to a signature, forgers have sometimes fashioned an accurate reproduction of the writing, but with a type of blotter now being employed in banks, they will no longer be able to do this. The blotters are black, so that the ink is almost completely lost in the color. Besides this advantage, they are not so easily disfigured.

 

Raising a car with a twist of the wrist in a few seconds is accomplished with a compressed-air jack now on the market. It is operated from a service-station air line, or with a small container of air compressed to 120 pounds and released from the tube into the jack.



 



That a fireman's gas mask can be successfully used as a diver's helmet was demonstrated recently by Capt. C. H. Virdin, of the Los Angeles department. Wearing one of the masks, he remained submerged for twenty minutes. It is thought that the equipment would prove of special service to companies detailed along water fronts or where emergency calls for rescues of drowning persons are likely.

 

Centers of industry and population of the United States are gradually moving westward toward the center of agriculture and the latter, in turn, is a bit nearer the geographical center of the country than it was a few years ago. The industrial center has moved seventy-five miles south and west in the last eighteen years, and is now in northern Indiana. The center of population is also in Indiana, in Owen county, 170 miles south and slightly west of the industrial center and almost at the Illinois state line. The agricultural center is about thirty-five miles southwest of Hannibal, Mo.. and the geographical center near the middle of the northern boundary of Kansas, close to Nebraska.

