21 
Facts and Observations. 
NEW METHOD OE VENTILATION. 
In arranging his plans for ventilation, McKinnell takes 
advantage of two simple and well-known facts. If an aper¬ 
ture is made, or a shaft carried through the ceiling of any 
room, or roof of any building, two currents of air are at once 
established; and these two currents, instead of jostling each 
other with human perversity, pass uniformly in definite 
courses according to fixed laws. The centre of the opening 
is occupied by an out-draught of the warm exhausted air of 
the building, while the sides are lined with an insetting 
current of the colder and purer atmosphere. One shifting 
column of air is contained within the other, and the two have 
a relative movement somewhat like that of the pieces of a 
telescope. Any one may illustrate this fact of the regular 
self-inclosed movements of fluids, of differing temperatures 
and densities, by warming a little water containing a few 
floating coloured particles, in a test tube, over a spirit-lamp. 
Directly the heat is applied, the coloured matter will indicate 
the presence of two opposite currents, in the positions and 
directions just mentioned. McKinnell carries two funnels 
or shafts, of different sizes and lengths, through the roof of 
the building he wishes to ventilate. The smaller and longer 
tube is placed in the centre of the larger one, and thus the 
two currents of air, naturally seeking to pass into and out of 
the apartment, are separated one from the other; and this 
concentric arrangement of the two tubes is so devised that 
the capacity of the central tube shall be equal to the annular 
space inclosed between its outer circumference and the inner 
aspect of the external concentric tube. The lower end of 
the inner tube is moveable, and has an expanding mouth¬ 
piece or flange. This trumpet-shaped expansion serves two 
purposes; if drawn down away from the outer tube, it spreads 
the incoming cold air over the upper part of the room, and 
so causes its descent to be more uniform and dispersed ; it 
may also, by being raised to the level of the inner opening 
of the outer tube, be made to act as a valve shutting out 
altogether the external air, or limiting the currents to the 
area of the central tube .—Medical Times and Gazette . 
