These “Wind and Current Charts” included Track Charts, Trade Wind Charts, Pilot Charts, Thermal Charts, Storm and Rain Charts, and Whale Charts. The Track Charts showed the frequented parts of the ocean, the general character of the weather and wind, and the force and direction of the latter at different seasons of the year. The Trade Wind Charts gave the limits, extent, and general characteristics of the trade wind regions, together with their neighboring zones of calms. The Pilot Charts showed in every square of fifteen degrees the direction of the wind for sixteen points of the compass that would probably be found in that square during each month of the year, the results being based upon the number of times the wind was reported to have been from that direction in former years. The Thermal Charts recorded the temperature of the surface of the ocean wherever and whenever it had been observed, the different temperatures being distinguished by colors and symbols in such a manner that mere inspection of the chart showed the temperature for any month. The Storm and Rain Charts demonstrated in every square of five degrees the number of observations that had been made for each month, the number of days in which there had been rain, a calm, fog, lightning and thunder, or a storm and the quarter from which it had blown. The Whale Charts, finally, showed where whales were most hunted, in what years and months they had been most frequently found, whether in shoals or as stragglers, and whether sperm or right whales. Though the coöperation which Maury enjoyed was an extensive one, he was still not satisfied, and as early as 1851 he conceived the idea of a universal system of meteorological observations on both land and sea. Through the advice of British scientists, he decided to confine his system, for the time being, only to the sea, though he was afterwards to regret such a curtailment of his original scheme. With the authority of Secretary of the Navy William A. Graham, to whom Maury was greatly indebted for very generous support in furthering his ambitious project, he set to work through diplomatic representatives of foreign countries at Washington to interest as many meteorologists as possible in the convening of an international meteorological conference. The United States also was asked to coöperate, through letters which Maury sent to the various Cabinet Members, heads of the Coast Survey, the Bureau of Engineers, and the Smithsonian Institute, and other scientists. Paris was at first considered to be a suitable place for the meeting; but eventually Brussels was chosen, and the following nations accepted the invitation to send representatives: Belgium, Denmark, France, Great Britain, Netherlands, Norway, Portugal, Russia, Sweden, and the United States.