Communication-通讯

Whn mn bgan to lik togthr in small communitis, thy it was ncssary to find ways of snding mssags from on community to anothr. vn in arlist tims thr wr svral diffrnt ways this could b don. Rally rapid communication was not possibl until lctricity was put to work. In 1844 th first lctric tlgraph was constructd. Thirty yars latr th tlphon was invntd. Soon a whol succssion of invntions was producd: th wirlss tlgraph and th radio, th motion pictur, and tlvision. arth satllits today bring valuabl information almost instantanously to our homs by mans of lctrical signals.