The immediate steps now in course of adoption may be explained in a few words. At present the transit across the Isthmus of Panama occupies four days, and its inconveniences and dangers are notorious. At Nicaragua, it is represented, the transit may possibly be effected in one day, and this by a continuous steam-route with the exception of fifteen miles by mule or omnibus. The passage would be up the San Juan, across Lake Nicaragua to the town of that name, and thence to the port of San Juan del Sur on the Pacific. On arriving at this terminus, (which is considerably south of the one contemplated for the permanent canal, namely Realejo,) the passenger would find himself some six or seven hundred miles nearer to California than if he had crossed at the Isthmus of Panama; and as the rate of speed of the American steamers on this service is upward of three hundred miles a day, his saving of three days in crossing, coupled with the saving in sea distance, would be equivalent to a total of fifteen hundred miles, measured in relation to what is accomplished by these vessels. A lower charge for the transit, and a comparatively healthy climate, are also additional inducements; and under these circumstances, anticipations are entertained that the great tide of traffic will be turned in the new direction. This tide, according to the last accounts from Panama, was kept up at the rate of 70,000 persons a year; and it was expected to increase. The navigability of the San Juan, however, in its present state, remains yet to be tested. The American company who have obtained the privilege of the route have sent down two vessels of light draught, the Nicaragua and the Director, for the purpose of forthwith placing the matter beyond doubt. At the last date, the Director had safely crossed the bar at its mouth, and was preparing to ascend; the Nicaragua had previously gone up the Colorado, a branch river, where, it is said, through the carelessness of her engineer, she had run aground upon a sand-bank, though without sustaining any damage. The next accounts will possess great interest. Whatever may be the real capabilities of the river, accidents and delays must be anticipated in the first trial of a new method of navigating it: even in our own river, the Thames, the first steamer could scarcely have been expected to make a trip from London Bridge to Richmond without some mishap. Should, therefore, the present experiment show any clear indications of success, there will be reasonable ground for congratulation; and it forms so important a chapter in the history of enterprise, that all must regard it with good wishes.