406 TRANSACTIONS OF THE 



an inch below the normal;" this intersection (marked "a") is your position 

 on the diagram; for, by the method of construction just explained, this is 

 the place, and the only place, where the wind is E.S.E., and, at the same 

 time, the barometer .20 of an inch below the normal. Referring to the 

 compass and scale which accompany the diagram, you will find that the 

 center (low) bears S.W. by S., distance two hundred and fifty-two miles. 

 Plot this position of the center on your track chart from the 4 p. m. position 

 of your vessel. 



Later in the day, say 8 p. m., suppose that the wind is S.E. by E., and 

 the barometer is .30 of an inch below the normal (having fallen .10 of an 

 inch in the interval) : With this wind your position must be half way be- 

 tween the dotted lines leading in toward the center from the arrows marked 

 "S.E." and "E.S.E.," and with this barometer reading it must be half 

 way between the isobars marked ".20" and ".40" below the normal; it is, 

 therefore, at the point marked " b," and the center bears " S.W.," distance 

 two hundred miles. Plot this 8 p. m. position of the cyclone center on your 

 track chart from the 8 p. m. position of your vessel. 



You have thus the position of the cyclone center at 4 p. m. and at 8 p. m. 

 plotted on your chart, and the dotted line joining the two positions is the 

 track of the center and the distance it has moved in four hours. 



Suppose, again, that at 10 p. m. the wind is still from S.E. by E., but 

 the barometer stands at .40 below the normal, having fallen .10 in two 

 hours. Your position is now at the point marked "c" on the diagram, found 

 by exactly the same course of reasoning as before, and the center now bears 

 S.W., distant about one hundred and seventy-five miles. Plot this 10 

 p. m. position of the center on your track, chart, from the 10 p. m. position of 

 your vessel. If you have been lying-to, this will evidently indicate that 

 the storm's track has recurved, and that you are directly in front of the 

 center. But, no matter whether you have been lying-to or not, your vessel's 

 track and the track and position of the cyclone center are both plotted on 

 your chart, and you can closety watch every change in relative position in 

 order to avoid the center and dangerous semicircle of the hurricane. 



NOTES ON REVOLVING STORMS. 



The subject of revolving storms, cyclone, hurricane, or tornado, has been 

 made the subject of a special bulletin of the Branch Hydrographic Office 

 of this city. The information is for the special benefit of mariners, and it 

 will be to their interest to note carefully the statements therein contained, 

 and they can compare them with their experience. The following are the 

 notes: 



EARLIEST INDICATIONS. 



Barometer above the normal, and continuing so quite noticeably for sev- 

 eral days, with dry, fresh, fair weather and uncommonly transparent atmos- 

 phere. The formation, in increasing quantities, of light, feathery, cirrus 

 clouds, and the setting in of a long, low, ocean swell from the direction of 

 the approaching storm. The long lines of filaments of cirrus clouds also 

 often indicate the bearing of the storm-center while it is still hundreds of 

 miles away, as they radiate from it on every side. As the cirrus clouds 

 gradually thicken, halos begin to appear about the sun and moon, and the 

 ocean swell increases. 



