126 Progress in Physks. [January, 



as it assumes a spiral motion of the air in the storm ; an ascending current at 

 its centre, and a descending counter current outside. The admission is made 

 that the relative influences of the respective causes of these motions cannot be 

 exactly determined. The explanation given of the effect of aqueous vapour is, 

 however, very good. The precipitation of this vapour as rain is acknowledged 

 to be a very active agent in depressing the barometer, and, according to 

 M. Mohn, the direction and rate of advance of the storm area is determined 

 mainly by it. He illustrates this statement by the following instance : — 



When a storm is advancing across the Atlantic its velocity is great, and its 

 motion is towards the east, owing to the fact that the vapour is transferred 

 over the sea surface so rapidly from the great reservoir of this element, lying 

 to the south of the trajectory of the centre, that it sweeps round in the spiral 

 to the front of the storm, and falls there with a S.E. wind. 



When the storm reaches Norway the condensation is accelerated by the 

 action of the coast, the barometer at the centre sinks lower, and the rain falls 

 principally with S.W. winds, as mechanical obstacles prevent the free 

 passage of the moist air to the point where it would blow as a S.E. wind. 

 This change in the conditions causes the greatest barometrical variation to be 

 very local, and to be situated to the south-east of the centre. The depression 

 at the centre becomes more serious, the storm slackens in its rate of progress, 

 and begins to move towards the south. 



When the disturbance has crossed into Russia the supply of vapour is drawn 

 from the Mediterranean. The air which brings it is partially dried in its 

 passage over central Europe ; so that by the time it arrives at the storm region 

 we find that the rain falls with westerly winds, the barometer falls fastest to 

 the south of the centre, and the easterly component of the advance of the 

 depression is entirely cancelled. The rain is less in absolute quantity, so that 

 the depression is not " fed " with moisture, and the whole storm gradually 

 disappears. 



Similar principles are applied to explain the phenomena of the storms of 

 North America, and of tropical cyclones. 



It is stated that since the opening of the present war in Europe that part of 

 Germany in the vicinity of Frankfort has been almost constantly visited by 

 rain and thunder storms, a most unprecedented thing at this season of the 

 year. In the light of other recorded facts, the German press has almost 

 unanimously attributed these unusual storms to the firing of cannon and small 

 arms in Alsace and Lorraine. The attention of scientific men is, however, 

 so well directed to observation of the meteorological events succeeding heavy 

 cannonading that the question of the correlation of artillery discharges with 

 rainfall will eventually be settled. The " Ungarische Lloyd," in an interesting 

 article on this subject, says that the history of the wars of the last eighty years 

 are full of accounts of the great meteorological changes which have followed 

 violent engagements in war. In 1861 Lewis, in an article in Silliman's 

 "American Journal," said: — "In October, 1825,1 observed a very plentiful 

 rain immediately after the cannonading which took place in celebrating the 

 connecting of Lake Erie with the Hudson. I published my observations on 

 this event in 1841, expressing the opinion that the firing of heavy guns 

 produces rain in the neighbourhood. After the first battle in the last war 

 between France, Sardinia, and Austria, there followed such important rains 

 that even small rivers were impassable, and during the great battle of Solferino 

 there broke out such a violent storm that the fighting was interrupted. In 

 July, 1861, M'Clellan's troops on the Upper Potomac had four separate 

 engagements on four days, and before the close of each violent rains fell. On 

 the 21st of July Bull Run was fought in Virginia, and on the 22nd rain fell the 

 whole day till late at night. Under the heading, ' Can we Produce Rain when 

 and where we like ?' the Cincinnati ' Woechtenliche Volksblatt ' for the 10th 

 of July, 1862, remarked : — ' The cannonading (during the war) on the York 

 River and James River, as well as the cannonading of Corinth and on the 

 the Mississippi, were followed by such fearful storms that the land was 

 inundated.' The Bohemian campaign of 1866 was accompanied during the 

 whole course by violent rains." 



