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. VELOCITY AND PRESSURE OF THE WIND. 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. +-------------------------------------------------------------------+ |Pressure in | |lbs. per | |Square Foot. | | |Velocity in | | |Miles | | |per Hour. | | | |Pressure in | | | |lbs. per | | | |Square Foot. | | | | |Velocity in | | | | |Miles | | | | |per Hour. | | | | | |Pressure in | | | | | |lbs. per | | | | | |Square Foot. | | | | | | |Velocity in | | | | | | |Miles | | | | | | |per Hour. | | | | | | | |Pressure in | | | | | | | |lbs. per | | | | | | | |Square Foot. | | | | | | | | |Velocity in | | | | | | | | |Miles | | | | | | | | |per Hour. | | | | | | | | | |Pressure in | | | | | | | | | |lbs. per | | | | | | | | | |Square Foot. | | | | | | | | | | |Velocity |