622 Proceedings of the Royal Society 
indicate the spots at which real pressure actually exists. This 
may illustrate the result of the present mode of construction in 
which the existence of real pressure is assumed. 
2. Charts of Dynamical Pressure. — If barometric charts, instead 
of exhibiting real, are supposed to indicate dynamical pressure, this 
also can be exhibited graphically, and such portions of its curve 
also be made comparable by using figures of equal observed pres- 
sure, corrected, however, to represent those of equal dynamical 
pressure through which the curve will be drawn. As in the former 
case, such a chart will not be one of isobarics ; it will be one of 
isodynamics, and will indicate approximately the spot at which 
real pressure exists. 
Such a chart, therefore, will more nearly represent the real state 
of pressure than one of the ordinary construction, because in few 
or no instances, over the area usually embraced by it, is the 
atmosphere in a state of perfect rest, hence real pressure is not 
often found to exist. In this instance of graphical delineation to 
exhibit dynamical pressure, an extension of the isobars will take 
place, but to a greater extent in front than in the rear, though the 
extension will not be so great as in the former instance. 
3. Curve of Isorhoics. — Such a curve as this, which represents 
uniformity of inflow in the various segments, besides aiding the 
correction of the barometer, will also increase the reliability of the 
gradients on which they depend. 
Lifting . — It is generally assumed that the force of the wind 
depends on the steepness of the gradients, and not on the absolute 
height of the barometer. In the “ English Meteorological Ma- 
gazine,” for June 1869, Strachan, however, shows that strong winds 
generally are also accompanied by a remarkable reduction of 
pressure. This takes place mostly with equatorial winds, attended 
also, as shown in a diagram, with the greatest barometric oscilla- 
tions. The reason of this is, that these winds are fed from a 
horizontal source of supply, and are drawn over a resisting surface 
often of great inequality. Under these circumstances “ lifting ” 
takes place. With polar winds, which have a vertical source of 
supply, removed from proximity to a resisting surface, fewer 
oscillations take place, and the barometer often rises. Jenyns has 
shown that, unlike the thermometer, the barometer rarely rises 
