75 



Will no member of this Society utilise the observations alreacly 

 registered, together with those daily presented in The Mercury 

 for the purpose of aiding science to the benefit, sooner or 

 later, of our mercantile marine ? I have no qualifications, 

 and, if I had, no time. But, from the wish to stimulate 

 others, I desire to offer a few, and, I hope, useful, if not very 

 original, remarks. Perhaps the seed may fall upon the soil 

 of one of our A.A's. who has distinguised himself as a student 

 of natural philosophy. I am myself content to point out to the 

 enquirer the gain that science has already made. We now 

 know that the general character of storms over the world is 

 circular, or, more strictly, elliptical. A storm is but the name 

 for the behaviour of the atmosphere attempting " to flow in 

 upon a central area (to use Buckan's words) of loio pressure 

 in an inmoving spiral course." But as we find that such 

 inflow does not, as we might expect, increase the deficient 

 pressure, Buckan concludes that within and about the centre 

 of the storm there is a vast ascending current arising into the 

 upper regions of the atmosphere, and then flowing over to 

 the right and left. These storms or hurricanes are never 

 known to cross the equator, but they always move obliquely 

 from their starting point towards one or other of the poles. 



Again, we may accept it as the most fundamental axiom of 

 the science of " weather prophecy " that the direction and 

 intensity of the wind depends, not so much upon the state of 

 the barometer in any given place, as upon the harometric 

 gradient. By this is meant that if the barometer stands at 

 a different height in two localities near to each other, such 

 difference in atmospheric pressure will produce disturbance, 

 and the amount of such disturbance will depend upon two 

 things — the difference as indicated by the barometer in the 

 two places, and i\iQ proximity oi the places one to the other. 

 I may illustrate this by the gradient of an inclined plane, 

 which depends not only upon the height but the length of 

 base of the triangle. In this exaggerated analogy the height 

 represents the barometric differences in two places, while the 

 base represents the distance between the two places them- 

 selves. The violence of the storm will depend upon the 

 angle of inclination, i.e., the ratio between the height and 

 base, which in the language of trigonometry might be con- 

 veniently called the tangent of the angle of inclination. 



If every other rule is of doubtful trustworthiness, in the 

 science of weather prediction, this fundamental principle of 

 the barometric gradient has been fully established. * The 

 advent as well direction of the storm has been familiarly 

 expressed by Ballot's law, " Stand with your back to the wind, 

 and the barometer will be lower on your left hand than on 



