354 Prof. C. Piazzi Smyth's Meteorological 



place of observation ; and as this is a cardinal point in the hurricane 

 theory, it was far too precious to be lost. 



The Rev. H. Lloyd of Dublin has, however, removed the diffi- 

 culties which had beset this case, by his investigations relative to 

 a hurricane of the whirlwind description which passed over Ireland 

 in November last. The Royal Irish Academy has recently estab- 

 lished, it seems, a very extensive system of meteorological observa- 

 tion over the whole of Ireland, and the development of the nature of 

 this " cyclone," is one of the first fruits which has followed. It 

 seems to have passed almost centrally over the country, and the ob- 

 servations at all the stations are as coincident as in any case yet pro- 

 duced between the tropics ; and have enabled Professor Lloyd to 

 determine the whole diameter of the whirl = 500 miles, the pre- 

 ceding radius = 230 miles, the following radius = 270 miles, the 

 velocity of the motion of the centre = 14 miles per hour, the velo- 

 city in the whirl =40, the direction of the general progress from 

 WSW. to ENE.,* and the diameter of the quiescent portion in 

 the centre = 50 miles. These last numbers, therefore, combined 

 with the rate of general motion of the whirl, shew that the change 

 experienced in the direction of the wind, by being first in one half, 

 and then in the other half of the whirl, cannot well be sudden, and 

 that there is more than abundance of time for a very slowly acting 

 cumulative machine, to adapt itself to the change of direction, with- 

 out being caught by a current exactly 180° from a former one, and, 

 therefore, perhaps acting for a time in a similar manner. 



I do not know whether these facts shewed Mr Osier the possibil- 

 ity of applying the cumulative methods with advantage, but he has 

 been engaged in applying such principles to his instrument for some 

 time past. For the strength of the wind he employs Mr Edge- 

 worth's elegant method of the hemispheres on the spokes of a hori- 

 zontal wheel ; all the concavities being turned in one direction, the 

 centre of the hemisphere moves at one-third the velocity of the wind. 

 In addition to this slowness of motion being in strong gales a mate- 

 rial advantage over Mr Whewell's vane-wheel, — where there seems 

 an impossibility in the little revolver to keep up on such occasions 

 its full proportion for light airs, — there is the further merit of Edge- 

 worth's being independent of the direction of the wind ; and capable, 

 when once a particular size has been agreed on, of being made by 

 any mechanic in any part of the world, from numerical description 

 only ; and so exactly, that every such instrument can be used at 

 once, without previous comparison with a standard. 



For the mean direction, of the wind, Mr Osier employs a plan 



* This direction should carry the cyclone south of Edinburgh, and accordingly 

 such appears to have been the case, by the record of the Osier anemometer on 

 the Calton Hill; which also seems to shew, that it was gradually separating 

 into two whirls ; or that, at all events, two, partly mixed on their neighbour- 

 ing sides, must have passed to the south of Edinburgh about that time. 



