_b_ denotes blue sky, whether with clear or slightly hazy atmosphere. _c_ „ cloudy, that is detached opening clouds. _d_ „ drizzling rain. _f_ „ fog. _h_ „ hail. _l_ „ lightning. _m_ „ misty, or hazy so as to interrupt the view. _o_ „ overcast, gloomy, dull. _p_ „ passing showers. _q_ „ squally. _r_ „ rain. _s_ „ snow. _t_ „ thunder. _u_ „ ugly, threatening appearance of sky. _v_ „ unusual visibility of distant objects. _w_ „ wet, that is dew.
A letter repeated denotes much, as _rr_, heavy rain; _ff_, dense fog; and a figure attached denotes duration in hours, as 14_r_, 14 hours’ rain.
By the combination of these letters all the ordinary phenomena of the weather may be recorded with certainty and brevity.
_Examples._—_bc_, blue sky with less proportion of cloud; _cb_, more cloudy than clear; 2_rrllt_, heavy rain for two hours, with much lightning, and some thunder.
The Pressure varies as the Square of the Velocity, or _P_ ∝ _V_^2. The Square of the Velocity in Miles per Hour multiplied by ·500 gives the Pressure in lbs. per square Foot, or _V_^2 × ·005 = _P_. The Square Root of 200 times the Pressure equals the Velocity, or √(200 × _P_) = _V_.
The subjoined Table is calculated from this data, by COL. SIR HENRY JAMES, of the Ordnance Survey Office.