The Beaufort scale of winds

Transcription

1 its relevance, and its use by sailors F. Singleton Lightwater, Surrey Mariners have always recognized qualitative gradations in wind; for centuries, in accounts of their voyages, they have used such words in common usage as air, breeze and gale with various adjectival qualifications, but without any agreed definitions. An early suggestion for creating a standard scale of winds was made by Daniel Defoe (1704) after he had witnessed and described the Great Storm of Even as late as the early nineteenth century, however, there was still no common standard nationally or internationally for ship captains to enter wind conditions in their logbooks. British seamen were converging on a scale of 12 or 13 points although European sailors used a variety of scales ranging from as few as 4 up to 10 points (Kinsman, 1969). On 13 January 1806, Commander Francis Beaufort of HMS Woolwich wrote in his logbook that he would use a 0 13-point scale to which he gave descriptive names (Table 1). The bicentenary of this event was celebrated by a meeting at Greenwich organized by the Royal Meteorological Society and the National Maritime Museum. Although long regarded by some as a seminal event, recent studies have shown that this is far from the case. For example, Table 1 Beaufort s scale (1806). 0 Calm 1 Faint breeze or just not a calm 2 Light air 3 Light breeze 4 Gentle breeze 5 Moderate breeze 6 Fresh breeze 7 Gentle, steady gale 8 Moderate gale 9 Brisk gale 10 Fresh gale 11 Hard gale 12 Hard gale with heavy gusts 13 Storm Walker (2006) in an article about the weather observations made on Vancouver s circumnavigation from 1791 to 1795 notes that, from copies of his diaries, it is clear the observer, Archibald Menzies, used a scale almost identical to that in Table 1. From Gale Force 10, the biography of Beaufort by Nicholas Courtney (2003), it seems that Beaufort was being evolutionary rather than revolutionary. His 1806 logbook entry should be seen in its historical perspective and the following is a brief summary of this fascinating topic. In a pamphlet, Practical Navigation, Alexander Dalrymple (1779) presented a TABLE of COMPARISON of WINDS from Ship s Journals with Mr SMEATON s Scale from Austhorpe Mill [sic]. A scale quoted by Dalrymple, using numbers 0 to 12 and descriptive names, is compared with Smeaton s 8-point scale. Each point of the latter had a number, name and a description that referred to the speed of rotation of a windmill with 34-ft-long (10m) sails and the resultant movement of, or noise from, leaves, branches or trees. Similar descriptions are used today in the land observer s version of the Beaufort scale. John Smeaton, a British civil engineer, had invented an early form of anemometer as part of his study of windmill design (Smeaton, 1759) and defined his scale of winds from the results. Dalrymple, Hydrographer of the Honourable East India Company, with which Beaufort had served his sea-going apprenticeship, wrote Practical Navigation to guide company captains in the completion of the ship s journal log or logbook in current terminology. He defined how and when to record meteorological observations and, in doing so, used single- or double-letter abbreviations for observed weather very similar to those used later by Beaufort and still used today in weather reports. Although the pamphlet contained his own presumably the company s scale of winds, apparently, and perhaps surprisingly, Dalrymple did not specify what he meant by wind terms such as fresh breeze. Probably, he thought it unnecessary because his captains were experienced seamen and worked to the common, but unwritten, standards of the day. In 1801, Colonel James Capper, also of the Honourable East India Company, produced a table relating wind forces in descriptive terms to the wind speeds in miles per hour, feet per second and pressure in pounds per square foot (Capper, 1801). Although interesting to researchers trying to assess wind speeds from logbooks, this did not help mariners of the time to standardize their recording of wind force. Dalrymple was probably in contact with his French counterparts because he gave the French equivalent terms for the various forces. This suggests that French sailors were also coming to a scale of around 12 points. Like the English terms used by Dalrymple, these are much the same as those of today. Not surprisingly, Beaufort was highly influenced by Dalrymple; in his 1806 scale, he used very similar descriptive names but added an extra, fifth, point which he called a moderate breeze. Wheeler and Wilkinson (2004) have studied the provenance of scales of wind on the basis of a comprehensive survey of ship logbooks from the mid-seventeenth century. This was part of the work involved in generating an EU-funded Climatological Database for the World s Oceans: 1750 to They studied the frequency with which words were used to describe wind strength and were able to identify a number of widely used terms. This, they suggest, implies the existence, by the late seventeenth century, of fairly generally accepted, if unofficial, scales of wind force. A specific example is William Dampier, the privateer, who made some very early perceptive observations on trade winds, coastal winds, typhoons, hurricanes and the effects of winds on ocean currents. In a book (Dampier, 1699) written after a circumnavigation it is apparent that he was using terms to describe wind force very similar to the Beaufort 1806 scale. A common feature of marine scales of the time, and of the Defoe scale, is that they depended on a general understanding of words in common usage but that were not defined either in terms of their effects or in any quantitative manner. It would seem that 37

2 the Beaufort 1806 logbook entry, in itself, was not particularly remarkable in that it simply followed the general pattern. The Smeaton scale as reproduced by Dalrymple seems to be an exception to the rule in that it contained qualitative definitions of the effects of different wind strengths on trees and branches, but, being land based, was of little use to mariners. The same is the case for Capper s quantitatively defined scale. The real and very significant contribution of Beaufort came in 1810 when, now as captain of HM Sloop Blossom, he defined, in his logbook, the sea-going characteristics of each point on his scale. His definitions are unlikely to be original in that he was, no doubt, reflecting collective marine experience of the time. Beaufort showed great foresight in recognizing the need for a standard and uniformly applied wind scale. In this respect, his scale has been and continues to be of great value to both operational meteorology and, importantly in these days of climate change concerns, also to climatology. It would be rather more meaningful to regard 2010 as the real bicentenary of the Beaufort scale of winds rather than Following discussion with Captain FitzRoy of HMS Beagle, and others, Beaufort refined the scale, now the 0 12-points version that rightly bears his name. In 1831, he submitted it to his seniors for official approval and in 1838 it was accepted by their Lordships of the Admiralty as the definitive scale to be used by all ships of the Royal Navy (Table 2). In 1854, FitzRoy, another great sailor, navigator and innovator, formed and became the first Secretary of the Meteorological Department of the Board of Trade, later the Meteorological Office. The scale Each force from 1 to 4 was described by Beaufort in terms of the speed of a man-ofwar under full sail on her fastest point of sailing clean full. This would correspond to the broad reach of a modern sailing yacht with the wind some 120 degrees off the bow. For forces 5 to 11 he used descriptions relating to the amount of sail that she could carry when in chase, full and by when the captain was carrying as much sail as possible in order to catch the enemy but without masts or spars being carried away. Clearly, this was a matter of very fine judgement; carry too little sail and the enemy would escape; too much sail and the same result would ensue. Neither would enhance the captain s reputation or career prospects. For a modern yacht, the equivalent of full and by would, most probably, be a fine reach or a close-hauled course with the wind some 40 degrees off the bow. A square-rigged vessel of the time might manage up to between 60 and 70 degrees off the bow. Even a sloop, like those commanded by Beaufort, could do little better. For a modern sailing yacht, as for a ship of Beaufort s time, the amount of sail carried has a critical effect on the performance of the boat. This is most evident when racing when there is, again, a fine balance between carrying so much sail that the yacht is heeling too much for optimum speed, or even suffers gear failure, and so little that opponents sail a faster course to the next mark. Neither wins races. The strongest wind, a force 12, was defined by the immortal phrase that which no canvas could withstand. In survival conditions, Beaufort saw no need to differentiate between higher strengths of wind. Modern versions of the Beaufort scale have higher numbers but, although important meteorologically, these are as irrelevant to the skipper of a sailing vessel now as they would have been 200 years ago. For a small vessel, any hurricane represents survival conditions. Even for a large ship, a force 12 or higher is extremely hazardous. The single word hurricane is quite sufficient in any forecast to draw attention to the severity of the expected conditions. The rationale for the 0 12-point scale, the level of precision, and the clarity implied by the definitions, have been well discussed in detail by Kinsman (1969) who also explained the significance of the various terms used and their relevance to a fighting ship of the day. The choice of the reference vessel to be a man-of-war, presumably a 74-gun ship of the line such as those at the battle of Trafalgar, rather than his own sloop is interesting. Probably he took the view that every sailor, whether officer or seaman, would be able to relate to such a standard ship. Thus, using his definitions, two sailors, even off different types of ship, could be quite clear about what was meant by a strong breeze, or whatever. The continuing use of the Beaufort scale today in marine forecasts, and weather reporting at sea and even on land, may be intuitively obvious to sailors but seem anachronistic to others; in fact, not all marine forecasts use the Beaufort scale. Scandinavian countries and Iceland, use the scientifically correct metres per second. Other countries, such as the USA and Croatia, use the mariner s unit of speed, the knot (nautical mile per hour). But, what are the advantages of the Beaufort scale and why do such maritime nations as the UK, France, Germany, Spain, Portugal, Italy and Greece all use a system based, initially, on the behaviour of early-nineteenth-century warships? What relevance has the scale for the meteorological community of the twenty-first century? Quite simply, in the marine environment, the Beaufort scale has four important advantages over what some may regard as more acceptable scientific systems: brevity, clarity, realism and relevance. Brevity To many in the UK, the archetypal marine forecast is the Shipping Forecast on BBC Radio 4. Because of constraints imposed by the BBC in order to aid timing of programmes, the forecast has to be capable of being read, more or less precisely, in three Table 2 38 Beaufort s 1831 version of the wind scale 0 Calm 1 Light air Or just sufficient to give steerage way 2 Light breeze 1 to 2 knots Or that in which a man-of-war with all sail set and clean full 3 Gentle breeze 3 to 4 knots would go in smooth water from: 4 Moderate breeze 4 to 5 knots 5 Fresh breeze Royals etc 6 Strong breeze Or that in which a well-conditioned man-of-war could just Single-reefed topsails and top-gallant sails 7 Moderate gale carry, in chase, full and by: Double-reefed topsails, jib etc 8 Fresh gale Treble-reefed topsails etc 9 Strong gale Close-reefed topsails and courses 10 Whole gale Or that in which she could scarcely bear close-reefed main topsail and reefed fore sail 11 Storm Or that which would reduce her to storm staysails 12 Hurricane Or that which no canvas could withstand

3 minutes. At BBC reading speeds, this equates to 330 words in total for 28 sea areas (29 with Trafalgar late at night) and roughly one million square nautical miles. Using knots, a forecaster might write for wind speed 8 to 15 increasing 17 to 25. A British forecaster will write 3 or 4 increasing 5 or 6. This is an important saving of one word, but five syllables. Apart from 7 and 11 every force in English is single syllable. In French, every force is single syllable and in German all are single apart from sieben. The skills honed by writing BBC shipping forecasts are equally useful when preparing forecasts to be read out over marine VHF radio by Coastguards at a Marine Rescue Coordination Centre (MRCC). Again, they are a valuable aid to brevity. This is also important for those oceanic areas of the world that are still served by voice broadcasts over HF or MF single-sideband radio transmissions. Even more important is the need for brevity in forecasts broadcast over NAVTEX. NAVTEX is a text over radio system used widely around Europe and many other parts of the world. Broadcasts, meeting international requirements, are all in English, on a single frequency of 518kHz at a fairly low power of 1kW by day and 0.25kW at night. The single-sideband transmissions have a normal ground wave range over the sea of up to around 300 nautical miles. Absorption of these frequencies by the D layer (the bottom of the Ionosphere) during the day prevents sky wave propagation. At night, sky waves and ducting under low-level temperature inversions can result in greatly extended ranges. Over the high seas, a similar service is provided via satellite communications using INMARSAT. NAVTEX stations broadcast in sequence in 10-minute time slots at a very slow speed, by modern day standards, of 100 baud roughly 100 bits/second. Hence it is important to avoid overrunning so minimizing the chance of interference with the next station to broadcast and that might be within range of intending recipients. Brevity is important if broadcasts, which include other marine safety information such as navigation warnings, are to be kept within the 10-minute limit. The NAVTEX Coordination Panel of the International Maritime Organization (IMO) has recognized that the UK NAVTEX forecast scripts provide a standard for all other countries. Clarity and realism Sailors may be listening to weather forecasts in bad weather, with poor reception or read by someone whose first language is not English. This may be on public service radio, such as BBC Radio 4, or marine broadcasts from MRCCs; they may be listening to forecasts in another language. Numbers, such as twenty-seven, thirty-three, dix-huit, trentesept and so on can easily be misunderstood. Single-syllable, simple numbers are much easier to understand whether in English, French, Spanish or many other languages with which the listener may have barely more than a nodding acquaintance. This is an important aspect as clarity aids understanding of forecasts and is vital to safety at sea, a prime consideration for all mariners. Weather wind in particular is never precise. Whether describing wind over a small area for even a short time let alone a large sea area for the next 24 hours, it is impossible, meaningfully, to use a single speed in knots or metres per second. A wind expressed in a single number such as force 4 recognizes that fact; the implication of a range is realistic. Using winds expressed in knots or metres per second may sound more scientific but, even when a range of speeds is quoted, there is an implication of precision that simply does not and cannot exist. All too easily, forecasters can fall into the trap of giving forecasts such as 5 to 15 becoming 6 to 16 (knots), rather than simply saying (force) 2 to 4 (a saving of four words). Anyone sailing the Adriatic will have heard Croatian forecasts using such wording. Relevance to ships All the points made above regarding brevity, clarity and realism are very appropriate but the relevance may not be quite as obvious at first sight. However, large vessels are prone to steering problems when manoeuvring at slow speed in harbours; large container vessels can all too easily lose deck cargo; vessels in ballast can suffer greatly when heavy weather causes pounding damage. In all cases, the captain will recognize the significance of a wind expressed as a force more readily than he will when the speeds are given in knots or metres per second. Perhaps more important is the use of the Beaufort scale in reports of weather from ships of opportunity. Despite advances in satellite observing techniques and the use of moored or drifting buoys, data from ships crossing the oceans are still, collectively, a valuable resource providing ground truth and very important surface-pressure values. Measuring wind from ships using anemometers is not, in general, a practical proposition because of the interference to the airflow in the vicinity of the ship caused by the ship s movement and its superstructure. A measurement in a clean airflow is very difficult to achieve. Bridge officers on ships can readily estimate the wind force using the descriptions of sea state defined by the World Meteorological Organization (WMO). An experienced officer will know how his vessel will behave in different sea conditions and, even at night, will be able to estimate wind within the terms of the Beaufort scale. These definitions have stood the test of time and one of Beaufort s major contributions to the science is that wind data from ships provide a reasonably consistent body of information capable of generating useful climatological data for the oceans. The wind speeds quoted in Table 3 are the result of studies which IMO (later, WMO) has adopted. Derivation of the wind-speed equivalences to Beaufort forces owes much to the work within the Meteorological Office of G. C. Simpson and others (Simpson, 1926). These equivalent values have been adapted for both marine observing and for use by observers on land when not equipped with anemometers. To the mariner it is not the speed in knots or metres per second that is important; it is the effect of the wind in terms of the sea state produced and on the handling of his vessel. Relevance to leisure sailors Leisure sailors go to sea for enjoyment even though sailing, like some other outdoor activities, involves high risk. To minimize risk, sailors learn a wide range of skills, such as navigation, pilotage, tidal stream and height calculations, boat handling, the correct use of marine radio, boat and engine maintenance and repair, and so on. Using weather information is a very vital skill, but one that many find difficult to acquire. A very significant merit of the Beaufort scale is its simplicity; importantly it can be interpreted easily, quickly and unambiguously. All are useful attributes when under pressure at sea, or when ashore and trying to make a decision about whether or not to go to sea. It is possible to define three categories of leisure sailors in terms of their need for and use of weather forecasts. First are ocean sailors, defined here as those making passages over distances that take weeks or months. These periods are well beyond the capability of deterministic weather prediction. Secondly, there are coastal sailors making passages that may last up to around five days, say across the North Sea or the Bay of Biscay. More generally, they will be fairly short, to or from a port or an anchorage, lasting up to 24 hours and often much less. Paradoxically, these sailors can be more at risk from the weather than trans-oceanic sailors. Thirdly, there are day sailors, leaving a mooring or beach and returning within a few hours. Sailors can, and most do, obtain weather information in a variety of ways other than the well-known Shipping Forecast on BBC Radio 4. The yearly published Admiralty List of Radio Signals, Volume 3, contains details of most broadcast marine weather forecasts. A comprehensive summary of these and other types of service useful to sailors can be found at The Beaufort scale of winds 39

4 40 Table 3 The Beaufort scale WMO sea-state specification Force Speed (knots) Sea state 0 <1 Sea like a mirror Ripple with the appearance of scales are formed, but without foam crests Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses Small waves, becoming larger; fairly frequent white horses Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in wellmarked streaks along the direction of the wind High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility Very high waves with long overhanging crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The tumbling of the sea becomes heavy and shock-like. Visibility affected Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected. 12 >63 The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected. Long-distance sailors Ocean-going leisure yachts typically sail at an average speed of around 5 knots. The slow vessel speeds, the large size of major storms, and the imprecision even of modern weather prediction, mean that they are generally unable to take advantage of weather routeing except, possibly, to ameliorate the effects of bad weather. Consequently, transoceanic sailors plan voyages using climatology. Typically, sailors will cross the Atlantic westbound late in the year, after the hurricane season, and in low latitudes; eastbound, they should try to reach the Azores before the first hurricanes and Western Europe before the first autumn storms. Weather forecasts will (or should) be used to determine when to leave port so as not to encounter bad weather while still near land. When on passage, weather information is used primarily as a warning service to make ready boat and crew in the event of bad weather being predicted. To cope with very bad weather, ocean-going yachts, normally, will be equipped with storm sails and sea anchors but both will take several hours to prepare. Winds up to force 7 or 8 should not be a problem for such yachts. It is when force 9 is exceeded that it may become really dangerous even for a well-equipped yacht with a competent crew. The definitions in Table 3 will be meaningful to such sailors, who may be in yachts as small as 10 m in length. They will have experienced sea conditions in a wide range of winds and will have a good idea about the implications in terms of safety of their vessel. Sea state over the open sea, important to all vessels, and especially to small sailing boats, is related, primarily, to the average wind. Using the information in Table 3, a forecast of wind given in terms of Beaufort forces, effectively of average wind conditions, will be a good indicator of sea conditions. Coastal and day sailors Most yachtsmen and women sail in coastal waters and often in relatively enclosed seas. Passages are planned to be completed within the period for which useful deterministic forecasting is a reality; possibly up to 5 days but generally no more than 24 hours and, often, confined to daylight hours. The vessels are unlikely to be equipped to oceangoing standards and, even if they were, they are usually too near the coast to be able to ride out a storm in safety. Avoiding bad weather is very important, and the prudent sailor will think and plan for the next few days. This is very different from the ocean sailor who has no option but to ride out bad weather when it comes. Many yachts can be sailed in winds as light as force 2 although speeds may then be too slow if the intention is to reach a port or anchorage by a specified time. Then, the auxiliary engine may well have to be used. Although, they can sail in strong winds, relatively few skippers will plan to go to sea with a forecast of force 6, sometimes known as the yachtsman s gale. First, shallowing water and tidal currents can cause conditions which make approaching ports difficult, even dangerous. Stronger-thanforecast winds may occur, perhaps because of sea breeze or other topographical effects; with the inherent variability in weather, winds can always be one force or so higher (or lower) than predicted. The acceptable sailing window for many coastal leisure yachts is rather small, between forces 2 and 5. This applies even more so to motor boats which can be difficult to handle, and very uncomfortable, in winds as light as force 4 with wind against tide. Day sailors will be concerned, primarily, with the detail of the weather over small areas, perhaps a 10- or 20-nautical-mile radius at most, and in the short term. They do not have to consider the weather for following days. Forecasts will give guidance on whether sailing will be possible or not today. However, the space-time resolution of the weather detail that the sailors would like to know about, and will, certainly, experience, is well below current, operational, numerical weather prediction capability. Very localized effects, so important to coastal sailing, especially racing, will not be well predicted. Most important will be local knowledge and experience, used, of course, in the light of relevant forecasts. For very small boats, such as sailing dinghies, similar ideas apply. The ubiquitous Mirror sailing dinghy is a little over 3m long and can be sailed in quite strong winds by youngsters. Its speeds are a few knots at most. A modern, high-performance GRP racing dinghy, some 4.5m long can get up to about 23 knots. The two boats will respond quite differently, but quite consistently, to different wind conditions. Sailors of both will regard a force 6 with some trepidation and neither would willingly go out sailing with a forecast of force 7 or more.

5 Interpretation of the Beaufort scale by coastal sailors Interpretation of marine forecasts is an essential first step both for planning and whilst at sea. The sea state will be highly dependent on such factors as bottom topography, coastal features, and wind or wave direction relative to a tidal stream or current. The descriptions in Table 3 will be neither very meaningful nor relevant to many coastal sailors. Beaufort s scale was derived in terms of the effect of the wind on a man-of-war of the time and his own sloops would have reacted rather differently. Similarly, whilst a modern yachtsman will know that a force 5 means winds of 17 to 21 knots, he or she will, more importantly, have to consider putting a reef in the mainsail and reducing the size of the headsail. It is a simple matter that becomes intuitive to most sailors, to relate a single number to the way in which their boats are likely to behave. The yacht riggers, Atlantic Spars, have suggested interpretations of the Beaufort scale (Table 4) that Beaufort might have developed had he been a modern-day yachtsman. The detail will depend upon the vessel as did Beaufort s original. A heavy, wooden boat dating from the 1920s will be a very different proposition compared with a lightweight modern GRP racing yacht, but the principles will still hold good. The skipper of each will have such a scale in his mind. Equally important is the well-being of the crew. All sailors will be acutely aware of what a force 5, 6 or whatever will mean to them personally. Such considerations may even override those relating to boat handling. Although the crew s version has been written with tongue in cheek, it is still a very valid and relevant way of interpreting a wind forecast given in terms of a Beaufort force. Few yachtsmen enjoy motoring; all enjoy the pleasure of a good wind and most do not mind some anxiety, or a little fear at times; it helps the adrenalin to run. Terror Table 4 The Beaufort scale for yachtsmen in the twenty-first century Skipper s version Crew s version 0 1 Drifting conditions. Boredom. 2 Set large sail to catch wind. Mild pleasure. 3 Large headsail and full mainsail. Pleasure. 4 Start rolling headsail. Great pleasure. 5 Reduce headsail further, one reef in mainsail. Delight. 6 More rolls in headsail, two reefs in mainsail. Delight tinged with anxiety. 7 Three reefs in mainsail and small jib. Anxiety tinged with fear. 8 Deep reefed mainsail. Fear tinged with terror. 9 Set storm jib and trysail. Great terror. 10 Survival conditions. Panic. and panic are not welcome. Inevitably, most sailors learn to interpret the Beaufort scale in its human implications as well as the boat-handling ones. Far from being a nineteenth-century anachronism, the Beaufort scale is still a meaningful and very useful tool in weather prediction and observation over both sea and land. Its simplicity, relevance and easy interpretation make a very real contribution to safety at sea. Long live Admiral Beaufort or, at least, his scale of winds. Acknowledgement I am grateful to Malcolm Walker who guided me through the fascinating history of wind scales. References Capper J Observations on the winds and monsoons illustrated with a chart, and accompanied with notes, geographical and meteorological. C. Whittingham: London. Courtney N Gale Force 10: The life and legacy of Admiral Beaufort. Headline Book Publishing: London. Dalrymple A Practical Navigation (Unpublished, copy held by the National Library of Scotland. Reproduced by Nicholas Courtney in Gale Force 10, ibid). Dampier W A discourse of tradewinds, breezes, storms, seasons of the year, tides, and currents. James Knapton: London. Defoe D The storm: or, A collection of the most remarkable casualties and disasters which happen d in the late dreadful tempest by both sea and land. London. Kinsman B Historical notes on the original Beaufort scale, Mar. Obs. 39: Simpson GC The velocity equivalents of the Beaufort scale. Met Office Professional Notes No.44, M.O., No.273d, (24 pages). Smeaton J An experimental enquiry concerning the natural powers of water and wind to turn mills, and other machines, depending on a circular motion, Phil. Trans. Royal Soc. 51: Walker M The weather observations of Surgeon Menzies. Weather 61: Wheeler D, Wilkinson C From calm to storm: the origins of the Beaufort wind scale. The Mariner s Mirror. 90: Correspondence to: Frank Singleton Farthings 43 Curley Hill Road Lightwater GU18 5YH franksingleton@clara.net Royal Meteorological Society, 2008 DOI: /wea.153 The Beaufort scale of winds The RMetS on-line shop is open for business If you are looking for a weather-related gift or book, why not browse in the RMetS on-line shop? Log on to You d be a mug not to. 41