B. TERRESTRIAL PHYSICS AND METEOROLOGY. 87 



given of its existence and progress. He thinks that the is- 

 suing of distinct weather prophecies, in the sense in which 

 that word is used in astronomy, would be quite premature ; 

 but that a statement of probabilities, such as has for many 

 years been published by the French government, and lately 

 by the United States, would be fairly proper. Monthly No- 

 tices of the Met. Society of the Mauritius, 1873, 27. 



UTILITY OF OCEAN METEOROLOGY. 



Sir Francis Galton has presented some interesting meteor- 

 ological statistics in connection with the solution of the ques- 

 tion of using such data for the purpose of determining the 

 best course for a ship whose sailing qualities are previously 

 known. He states that if we desire to estimate which of two 

 alternate passages between the same ports can be performed 

 most quickly on an average of many voyages, no knowledge 

 can be more immediately useful than that of the distance 

 which the ship can accomplish at various points of the route 

 in a unit of time. To obtain this knowledge it is necessary 

 to know the average currents and winds, and especially the 

 relative sailing qualities of the vessel according as it sails 

 with the wind or on either tack. To deduce this latter and 

 most important element in the calculation, Mr. Galton has in- 

 vented a machine, in which, when certain parts are pushed 

 forward, the points representing north, south, east, and west, 

 respectively, move through distances corresponding to those 

 over which the ship would sail toward those quarters of the 

 wind, and by means of such a machine, or by proper arith- 

 metical processes, a small chart is constructed, showing at a 

 glance the sailing qualities of the vessel. This chart is to be 

 laid upon each square of one or two degrees on the ocean's 

 surface, and made to indicate such changes as are necessary 

 to accommodate it to the winds prevailing in that region of 

 the ocean. The result of this is that we have a map of the 

 ocean, covered with small diagrams, each of which graphical- 

 ly shows the distance through which a given ship can be ex- 

 pected to sail during a unit of time say, one day in that 

 region, under the known average conditions of winds and 

 currents; and a very short study will show the navigator 

 who finds himself placed in any portion of the globe, with a 

 certain wind blowing upon his vessel, what sail to make in 



