194 OBSERVATIONS ON THE WINDS. 



show) sometimes follow each other very closely, and may be represented 

 by the line D I. Keeping Buys-Ballot's Law (page 113) in mind, let us 

 suppose that a ridge of high pressure (B) be experienced travelling to the 

 North-Eastward, we know that it would be accompanied by corresponding 

 winds, viz.. Northerly followed by Southerly. 



If merely a Depression (F), then Southerly winds would precede 

 Northerly. 



If SiBidge and Depression (G), then Northerly, Southerly, and Northerly, 

 would be the order of the winds. 



If a Bidge and Depression be followed by another Bidge (H), then 

 Northerly and Southerly changes would be twice experienced. 



Now it is hardly possible to look at the diagrams which accompany this 

 paper without perceiving that they give sections of disturbances which could 

 be explained by some one of the above cases. We may also suppose that 

 after they have passed over a ship, the winds will be inclined to take up 

 the normal direction as shown on the line ABC. 



If the reader can suppose such changes of pressure as are represented by 

 the line D I to be travelling to the North-Eastward over a sea which has 

 its normal pressure represented by the line A B C, he will get the idea we 

 wish to convey. 



In the course of this paper it has frequently been remarked that with a 

 steamer bound to the Eastward, the barometer was falling with a Northerly 

 and rising with a Southerly wind. Now it is quite clear that this would 

 always be the case with a steamer steering to the Eastward, if the atmo- 

 spheric pressure over the Atlantic were always in the normal state repre- 

 sented by the line ABO, and this order of rise and fall would be reversed 

 with a steamer bound to the Westward. 



Again, suppose it were possible that a steamer could go to the North- 

 Eastward faster than an atmospheric disturbance represented by the 

 depression F, and so cut through it, then it is clear that she would have a 

 falling barometer with a Northerly, and a rising barometer with a Southerly 

 wind; but if these disturbances move at a speed of 30 miles an hour, it ia 

 clear that a steamer could not outstrip them, but only keep longer under 

 their influence when steaming fast to the North-Eastward, than when 

 standing still or going to the Westward. Hence we may conclude that 

 when the barometer falls with a Northerly and rises with a Southerly wind, 

 as a ship steams to the Eastward, she is experiencing, either the normal 

 state of pressure, or a slowly moving disturbance. 



We give only two instances of the barometer falling in a Northerly wind, 

 with a ship steaming to the Westward, and they were both in the great 

 gale of February 5th. They seem to indicate that the depression was 

 increasing in intensity faster than the ships could move away from it. 

 Such cases should be considered as important warnings. 



The various extracts which follow the 8th of February, when an Easterly 

 wind set in on the North-Eastern part of the chart, and worked its way to 

 the South- Westward, seem to show that such a state of things does not 

 check the formation of cyclonic gales off the Coast of America, for they 

 were still experienced, and, judging from the Bermuda data, the North- 

 westerly winds were stronger. The routes which the gales took seemed, 



