514 



NA TURE 



[A/an-/i 31, 1887 



and Laboratory Report, June 1886, of which I inclose a marked 

 copy. It will be observed that while Ulrich accepts the identity 

 of the New Zealand alloy with oktibehite, Skey's analysis shows 

 that its formula is 2Ni + Fe, while that of the latter mineral is 

 Ni + Fe. James Hector 



N.Z. Geological Survey Office, Wellington, N. Z., 

 February 9 



AERIAL VORTICES AND REVOLVING 

 SPHERES 



A STRIKING series of experiments on aerial vortices 

 ■'*■ and revolving spheres has lately been made by M. 

 Ch. Weyher, one of the directors of the important 

 establishment for mechanical constructions at Pantin. An 

 account of these experiments, with illustrations, appeared 

 in a recent number of La Nature (February 26). As the 

 results obtained by M. Weyher are very interesting, we 

 reproduce the more important figures, and translate the 

 descriptions given by our French contemporary. 



Fig. I. — Aerial Vortices. — \ glass cylinder of about 

 o'4om. in diameter by 070m. in height, has an upper 

 cover, pierced by a hole through which passes the shaft 

 of the drum, the latter being formed of one or two 

 paddles of cardboard put cross-wise upon the vertical 

 shaft. 



The cylinder contains some sawdust, or, better still, 

 some oatmeal. If the oatineal is put at first so as to form 



a cone or mound, and if the drum is turned round, a little 

 waterspout can be seen forming at the top of the mound. 

 Gradually the mass of oatmeal sinks into a hemisphere. 



The matter runs without ceasing into spirals from the 

 circumference to the centre ; there it forms at first the 

 lower cone, and then the upper reversed cone, in which 

 the particles of oatmeal describe spirals, going from the 

 centre to the circumference. 



The whole system describes a primary general sphere, 

 more or less distorted, the centre of which (where the 

 two cones meet) is more or less deranged by the earth's 

 gravity. If this is looked at from above, a hollow funnel 

 is seen upon the axis : it is there that the air is most 

 rarefied by rotation, and it is there that the finest particles 

 come. 



Substituting for oatmeal in the apparatus small light 

 balloons inflated with air, the general movement can be 

 followed. When the balloons are on the exterior circum- 



ferences, they fall in slow spirals ; when they reach the 

 circumferences nearer the axis of rotation, they rise 

 rapidly upon a helix at a much more extended pace. In 

 short, the experiment shows that, given a mass of air, if a 



movement of rotation round a vertical axis is imparted to 

 it this air falls constantly by the exterior circumfer- 

 ences, and rises by the interior circumferences, and the 

 7uhole volume passes unceasingly through the centre of 



the vorte ;, drawing in'o it s movement the substances or 

 particles therein im nersed. 



Fig. 2. — \ plate of glass or any other material is placed 

 below a drum with paddl es ; when this drum is put in 



