Meanwhile a depression on the south coast of Texas on the 25th, moved across the Gulf of Mexico, passing over Southern Florida on the 27th and advanced steadily northeast, reaching Cape Hatteras in 24 hours. Owing to the presence of the anticyclone referred to above, the depression recurved off Hatteras. The result was a memorable snow storm in Northern Virginia and Maryland. At 8 p.m. January 27th, there had been a fall of 5 cms. (2 inches). Within the following twenty hours the average depth in the city of Washington was 66 cms. (26 inches). The weight of the snow caused the collapse of the roof of the Knickerbocker Theatre and the death of 97 persons. The total snowfall in various coast cities was: Raleigh 24 cms.* Richmond 48 " Washington 71 " Baltimore 67 " Wilmington 46 " Philadelphia 31 " Trenton 27 " New York 18 " New Haven 8 " Boston 1 " *Note: To convert to inches multiply by 0.4. The table shows clearly how the snow was formed. On the east side of the LOW a stream of air, relatively warm, carried a load of water vapor, approximately 13 grams in each cubic metre. [Illustration: BASE MAP BY GOODE FIG. 10. PATHS OF HIGH AND LOW, GREAT SNOW STORM OF JANUARY 27-28, 1922] This current was steered around the north side of the LOW and met the north-northeast wind. Under the new conditions the air saturated could hold only 2 or 3 grams; and so condensation and heavy precipitation resulted. The region of maximum snowfall was near Washington, and it will be seen that there is a proportional decrease north and south. The snowfall at Washington was the heaviest ever known at that city. Unlike most storms, there was no strong cold northwest wind blowing into the depression. The temperature rose slowly. It was less a contrast of winds than a steady slow outward push of the anticyclone, and the consequent turning of the path of the cyclone eastward. LAWS OF FORECASTING Buys Ballot's Law. "If you stand with your back to the wind the pressure decreases toward your left, and increases toward your right." For navigators, this law is more generally expressed in the words of the Hydrographic Office on "Cyclonic Storms." "Since the wind circulates counter-clockwise in the northern hemisphere, the rule in that hemisphere is to face the wind, and the storm centre will be at the right hand. If the wind traveled in exact circles, the centre would be eight points (90 degrees) to the right when looking directly in the wind's eye. But the wind follows a more or less spiral path inward which brings the centre from eight to twelve points (90 to 135 degrees), to the right of the wind. The centre will bear more nearly eight points from the direction of the lower clouds than from the surface wind." [Illustration: FIG. 11. SKIRON--THE NORTHWEST WIND]