;50 PROCEEDINGS OF THE 



ence of an observed pressure from that calculated on I call the departare of th« 



pressure positive when the pressure is greater, negative when it is less. Those 



departures, besides the obpervations of the other instruments, are communicated 

 :from post to post. The rule is now very simple. If the departures are greater 

 (more positive) in the southern places than in the northern, greater at M. or V. 

 than at G. or H., the wind will have a W. in its name ; when the departures are 

 greater in the northern places the wind will have an E, in its name. More accu- 

 rately, you may say, the wind will be nearly at right angles with the direction of 

 the greatest difference of pressures. When you place yourself in the direction of 

 the wind (or in the direction of the electric current) you will have at your leltthe 

 least atmospheric pressure (or the north pole of the magnet). When the differ- 

 ence of pressure of the southern places above the northern is not above four mil- 

 limetres there will be no wind of a force above 30 lb. on the square metre. More- 

 over, (he greatest amount of rain a ill fall when the departures are negative ; and 

 at the places where the departures are most negative, there also the force of 

 the wind will be generally etronger. Moreover, there will be no thunder if the 

 liarometric pressure is not less than two millimetres above the average height, and 

 when at the same time the difference of the departures of temperature is consid- 

 erable. Those rules, and especially the first two, were laid down by me, in 185Y, 

 in the Comptes Rendus, and on the 1st of June, 1860, the fiist telegraphic warning 

 by order of the Department of the Interior was given in Holland. It was unfor- 

 tunate that those telegraphic wrrnings were not introduced four days sooner, for 

 in that case the first communication would have been a first warning against the 

 fearful storm of May 28, 1860, called the Fiastcr-storm. All of you know hovr 

 amply Admiral Fitz Roy has arranged the telegraph warnings all over England. 

 — 2. Those rules used in Holland have behaved themselves very well, as is laid 

 down in the translation of a paper of Mr. Klein, captain of a merchant sh'p, where- 

 to I have added my observations and signals compared with the signals of Admi- 

 ral Fitz Roy in table A, p. 25. My own paper dates from June 1, I860, and is ex- 

 tracted by Ml-. Klein as you may see, but I preferred that the less complete and 

 precise paper of a practical man be translated, because I thought that the seamen 

 would put more reliance on it. From the tables added to that translation it ap- 

 pears that I have warned from my four stations, just as Admiral Fitz Roy has 

 done from his twenty. It must, however, be recorded that besides those four 

 stations, there are also some stations — Paris, Havre, Brest — in France, and some 

 in England — Hartlepool, Yarmouth, Portsmouth, Plymouth— tliat send me their 

 observations. Generally they ari'ive too lute, and therefore they throw but very 

 little light on the forecasting, principally while the barometers are not so well 

 known. So much for the strength, now for the direction. The direction ia in the 

 first twenty-four hours after the observations three times of the four such as indi- 

 cated, and the second 24 hours and the third 24 hours still two times of the three 

 Bucb as indicated (see table B, p. 29), and moreover no storm has occurred in 

 those six years when not before the difference of the southern departures above the 

 northern has been four millimetres. — To come to the third point. 3rd. What 

 is to be done ? The normal heights of the barometric pressure, or better, of the 

 barometers, which are read, must be conscientiously taken, the observation must 

 be made at more points once a day, and mutually communicated, and at days when 



