THE PACIFIC TELEGRAPH LINE. – We yesterday published a congratulatory message sent by Brigham Young – who, by-the-by, assures us that Utah is firm for the Union – on the opening of the Pacific Telegraph line to Salt Lake City, which took place at one P. M., on the 18th inst. We are therefore in direct telegraphic communication with the Mormons in Utah, and in a few weeks, we are informed, the line will be completed to the city of San Francisco. The work of the pony express will then be done in a twinkling, and New York and California will be within an easier speaking distance than New York and Coney Island. This will not only be very convenient, but of excellent effect in bringing the Californians nearer home, and making them feel, if possible, a deeper interest in everything transpiring in the Atlantic States. It will give an impetus to our California trade, and place us in possession of news from Japan and China within a month or six weeks. A few years ago such a project would have been laughed at; but now it is all but an accomplished fact. When we can exchange messages with California in one day, people of either ocean will be unwilling to suffer much delay in the transmission of letters by mail, and a more rapid postal communication is certain to follow. Thus, whichever way we look at it, this new feature in telegraphic enterprise presents a number of advantages, not only to the government and mercantile community, but to the public at large.