UC-NRLF QC S 7 / ]jU, fcj. GIFT OF CLOUD FORMS CIRRUS (MARE'S TAIL) ^Zl.OOOto 50,000 ft- CIRRO-STRATUS CIRRO-CUMULUS (MACKEREL SKY ) tC.CWv 23.000 6, ALTO-CUMULUS 10,0 00 to 26,000 A. ALTO-STRATUS 10.000 'to 23.000 & STRATO-CUMULUS CUMULUS 4,600 taG.OOO&. CUMULO-NIMBUS (STORM CLOUD) *,SOO to NIMBUS (RAHN CLOUD ) 3flOOto6,400& STRATUS to 3,500 A IV III CONDOR HI MA LAVAS" ANDES (ACONCAGUA] MONT BLANC MATTERHORN KITE BOSTON /&_ U.S. BEN NEVIS I V$ iNOWDON S 1 PAUL From Photographs by COL.H.M.SAUNDERS. By Permission of M" R INWARDS. HINTS TO flfoeteorological bservers. PREPARED UNDER THE DIRECTION OF THE COUNCIL OF THE ROYAL METEOROLOGICAL SOCIETY, BY WILLIAM MARRIOTT, F.R.Met.Soc, ASSISTANT-SECRETARY AND LECTURER. SEVENTH EDITION, REVISED AND ENLARGED. I VIT& JLL ufrkA TfDNS. ' V LONDON: EDWARD STANFORD, 12, 13 & 14 LONG ACRE, W.C CONTENTS. PAGE STATIONS OF THE ROYAL METEOROLOGICAL SOCIETY ... . . .5 INSTRUMENTS REQUIRED TO EQUIP A STATION ..... 5 BAROMETER. How to be mounted .... 6 Principle of the Fortin and Kew Patterns .... 6 ,, Attached Thermometer ..... 6 ,, Method of reading ....... 7 Corrections for Index Error . . . . .8 ?, Temperature . . . . .8 ,, Altitude ...... 8 ,, Method of preparing a Table to combine the three Corrections . 10 ,, Correction for Gravity . . . . . .10 ,, Management ....... 10 ,, Aneroid . . . . . . . . n THERMOMETERS. Negretti and Zambra's Maximum . . . .n ,, Phillips' Maximum . . . . . .11 5 Minimum . . . . . . .12 Dry-bulb and Wet-bulb . . . . .12 ,, How to mount the Wet-bulb . . . . .13 ,, Stevenson Thermometer Screen . . . .13 ,, Shelter for Tropical Countries . . . . .14 , , Method of reading the Thermometers . . . .15 Terrestrial Radiation. Grass Minimum Thermometer . 15 ,, Earth Temperatures. Symons's Earth Thermometer . .16 j> Solar Radiation. Black-bulb and Bright -bulb Thermometers in vacua . . . . . . .17 ,, Defects of Spirit Thermometers . . . .17 ,j ,, Phillips' Maximum . . . . .18 ,, How to restore the markings on the Tube . . .18 ,, Suspension of Thermometers . . . . .18 Thermometer Corrections . . . . .18 HYGROMETRY. Dew-Point . . . . . . .19 ,, Elastic Force of Aqueous Vapour . . . . .20 ,, Relative Humidity . . . . .20 RAIN GAUGE. Snowdon Pattern . . . . . . .21 ,, Exposure . . . . . . . .21 ,, Measurement of Rain . . . . . .21 SNOW. Measurement ........ 22 EVAPORATION ......... 23 PERCOLATION GAUGES ........ 23 WELL MEASUREMENTS . . . . . . -23 WIND DIRECTION ........ 24 ,, How to obtain the North Point . . . .25 ,, Equation of Time . . . . . .25 ,, Azimuth Compass . . . . . .26 ,, Westerly Variation of the Magnetic Needle, 1912 , 26 WIND' FORCE. Beaufort's Scale . . . . . . .26 ,, Dines' Pressure-tube Anemometer . . . .27 ,, Robinson Anemometer 28 241042 4 CONTENTS PAGE SUNSHINE RECORDERS. Campbell-Stokes . . . . -29 Adjustment . . 30 ,, Jordan Photographic . . . . . 31 ,, ,, Measurement of Record . . . . .31 OZONE ..... 31 CLOUDS. Estimation of the Amount . . . . ' . .31 International Cloud Nomenclature . . ...._. . 31 Motion and Direction of Upper Clouds . . -33 WEATHER. Entry of the State of the Weather, etc. . .' . . 34 ,, Beaufort's Notation and International Symbols . T . 34 HOURS OF OBSERVATION . ... . : . 34 NOTE-BOOK .... -35 LAMP . . . . . . . . . -35 REGISTER. Entry of Observations . . -i . . -35 ,, Sums and Means . . . . . . -35 ,, Determination of Mean Temperature . . . . 36 ,, Summary of Cloud and Wind Observations . . . .36 ,, Remarks on the Weather, etc. . . . . .36 SELF-RECORDING INSTRUMENTS. Thermograph . . . . -37 ,, Dry -bulb and Wet-bulb Thermograph . -37 ,, Barograph . . . . -37 ,, Hair Hygrograph . . . -37 ,, ,, Self-recording Rain Gauge . . .38 ADDITIONAL OBSERVATIONS. Kites and Balloons . . . -39 ,, ,, Photographs . 39 PHENOLOGICAL OBSERVATIONS. Plants, Birds, and Insects . . -39 BOOKS AND PUBLICATIONS ON METEOROLOGY . . . . -41 ENGLISH AND METRICAL SCALES . . . . . . .42 METEOROLOGICAL TERMS. . . * . . . . .42 TABLES TABLE I. Corrections to be applied to Barometers to reduce the observations to 32 Fahr. 44 II. Corrections for reducing observations of the Barometer to Sea-level, from 10 to 1000 feet . ; . . . . . .46 III. Specimen of the Table to be prepared for reducing observations of the Baro- meter to Sea-level, for a station at an altitude of 190 feet . . .50 IV. Corrections for reducing the Barometer readings for Gravity at Latitude 45 . 51 V. Specimen of the Table combining the corrections for Index Error, Temperature, and Altitude for a station 190 feet above the Sea-level . . .52 VI. For calculating the Dew-point Temperature . . . . .54 VII. Elastic force of Aqueous Vapour . . . . . .56 VIII. For calculating the Relative Humidity . . . . .58 IX. Comparison of the English and Metrical Barometer Scales . . .61 X. Comparison of the Fahrenheit and Centigrade Thermometer Scales . .62 XL Comparison of English Inches and Millimetres, for Rainfall Observations . 63 XII. Conversion of English Miles per Hour into Metres per Second . . 64 XIII. Conversion of Metres per Second into English Miles per Hour . . 64 XIV. Specimen of a Climatological Return . . . . .65 A GLOSSARY OF METEOROLOGICAL TERMS . . . . .66 ROYAL METEOROLOGICAL SOCIETY . . . . . -73. HINTS TO METEOROLOGICAL OBSERVERS. METEOROLOGICAL observations to be of scientific value must be made on a uniform plan, otherwise the results will not be mutually compar- able. The Royal Meteorological Society insists on such uniformity, and accepts observations from those persons only who comply with its requirements, and whose instruments on inspection are found to be satisfactory as regards both their quality and manner of exposure. The Stations of the Royal Meteorological Society are: (i) "Second Order" Stations (sometimes called "Normal Climatological" Stations), at which the observations are taken twice daily, at 9 a.m. and 9 p.m. ; (2) "Climatological" Stations, at which the observations are taken once daily, at 9 a.m. ; and (3) Stations at which one or more elements only are observed. When possible, observations are also taken at 3 p.m. at all stations. Instruments. The necessary instruments for a "Second Order" Station are: Standard Barometer ; Maximum Thermometer ; Minimum Thermo- meter ; Dry-bulb Thermometer ; Wet-bulb Thermometer ; Stevenson Thermometer Screen ; and Rain Gauge. At a " Climatological " Station the instruments required are : Maximum Thermometer ; Minimum Thermometer ; Dry-bulb Ther- mometer ; Wet-bulb Thermometer ; Stevenson Thermometer Screen ; and Rain Gauge. At each station the Stevenson Screen is to contain the four thermometers mentioned. It is desirable to have also a Minimum Thermometer (graduated on the stem, without attached scale) for terrestrial radiation ; one or more Earth Thermometers ; and a Sunshine Recorder. A Baro- graph ; a Self-recording Rain Gauge ; and an Anemometer (or prefer- ably, an Anemograph) are useful additions. Intending observers should purchase only the best class of instruments, and not those of a cheap or worthless character. The instruments should be verified at the National Physical Laboratory, so that the corrections for index error may be known. The thermometers must have the scales etched on the tube. HINTS TO METEOROLOGICAL OBSERVERS Barometer. The Barometer may be either of a Fortin or a Kew pattern. Tt should be mounted in a room not subject to sudden or great changes of temperature, must hang vertically, and should be in a good light, but not near a fire- place or stove. It is best to fix the instrument at such a height that the observer can read the vernier comfortably when standing upright. To facilitate readings a piece of opal glass or of white paper should be fixed immediately behind the part of the tube at which the readings are taken ; and if the barometer is of the Fortin pattern, another piece should be placed behind the cistern. The verticality of the barometer should be occasionally tested by unscrew- ing the clamping- screws at the bottom and seeing that the cistern hangs in the middle of the ring. As the mercury in the tube rises or falls, the level of that in the cistern changes in the opposite direction, and unless this change be taken into account, the readings will not be correct. In the Fortin barometer (Fig. i) this is done by making the cistern adjustable, so that the surface of the mercury therein can always be brought into contact with the ivory point which forms the extremity of the scale. In the Kew barometer (Fig. 2) the cistern is rigid, but the error arising from the change of level in the cistern (technically termed "the error of capacity") is com- pensated for by contracting the divisions on the scale, which by this means represent very approxi- mately inches of barometric pressure, though the divisions are actually somewhat shorter than true inches. Every barometer has a thermometer attached, in order to FIG. i. Fortin Barometer. FIG. 2. Kew Barometer. BAROMETER 7 show the temperature of the mercury in the barometer and of the brass tube which serves as the standard of measurement. By its means the observer can determine the proper correction to be applied to the reading of the barometer to reduce it to the standard temperature, that of the freezing-point, 3 2 Fahr. Before suspending the barometer it is desirable to test the vacuum. This may be done by gently inclining the instrument until the mercury touches the top of the tube, when a clear metallic sound should be heard. If no sound is heard, it may be inferred that some air has got into the tube, and consequently the readings of the barometer will be too low. Method of Reading-. The mode of taking an observation is this : First note the reading of the attached thermometer to the nearest degree ; then (if the barometer is a Fortin) adjust the mercury in the cistern by turning the screw at the bottom of the cistern, so that the ivory point is just brought into contact with the surface of the mercury, but does not depress it ; the ivory point and its reflected image in the mercury should appear to just touch each other and form a double cone. Then gently tap the tube with the finger, to prevent the mercury from adhering to the glass. Next adjust the vernier so that its two lower edges shall form a tangent to the convex surface of the mercury in fact, the front and back edges of the vernier, the top of the mercury and the eye of the observer must be in the same plane (Fig. 3). Move the head up and down to make sure that this is so. The scale on the instrument is usually divided into inches, tenths, and half-tenths, and the vernier, being made equal in length to 24 divisions of the scale, is divided into 25 equal parts. Each division of the vernier is therefore shorter than each divi- sion of the scale, by the 25th part of -05 ; which is -002 in. First read off the division next below the lower edge of the vernier. Suppose it be between 29-05 ins. and 29-10 ins., the reading is 29-05 ins. plus the vernier indication. Next look along the vernier until one of its lines is found to agree with a line on the scale. Suppose this is at the fourth divi- sion on the vernier ; as each of the figures marked on the vernier counts as a hundredth, and each intermediate division as two thousandths, the reading of the vernier will be -008 in. The reading of the barometer is therefore 29-05 + -008 = 29-058 ins. (Fig. 3). Should two lines on the vernier be in equally near agreement with two on the scale, the intermediate value should be adopted. For instance : suppose that the third and fourth divisions Barometer. 8 HINTS TO METEOROLOGICAL OBSERVERS above the figure 4 were one as much below, as the other is above, the lines on the scale, the vernier value would then be -047 in. The barometer reading would consequently be 29-05 + -047 = 29-097 ins. When it is difficult to say which division of the scale is that immediately below the lower edge of the vernier, the vernier reading will itself indicate which principal division should be taken. After the reading has been taken, if the barometer is a Fortin, the mercury in the cistern should be lowered by turning the screw at the bottom until the surface is well below the ivory point, other- wise dirt will collect and the mercury will oxidise immediately underneath the ivory point, and its reflected image will become indistinct. If the barometer is of the Kew pattern, no adjustment of the cistern has to be made, and the vernier is read exactly as with the Fortin. Corrections. The actual reading of the barometer requires to be corrected for (i) index error, (2) temperature, and (3) height above sea-level, in order to obtain comparable values. There is also a correction for (4) gravity, when it is desired to compare the readings with those made in other parts of the world. 1 i ) The correction for index error is that given on the certificate of verification ; if the barometer is a Fortin, the correction will be the same throughout the scale ; but if of the Kew pattern, it will probably differ in different parts of the scale, and should be applied accordingly. (2) As the mercury in the barometer and its brass scale both expand by heat, the height of the column is affected by change of temperature : it is therefore necessary to reduce the readings to a standard temperature; 32 Fahr. is that adopted. Table I. 1 (p. 44) gives these corrections for every half-inch, from 27-0 ins. to 31-0 ins., and for each degree of the attached thermometer from 20 to 100. In using the Table, first find the temperature in the left- or right-hand columns corresponding to that of the attached thermometer, then run the eye along the horizontal line to the column corresponding to that of the reading of the barometer, and the value there found is the correction required. Example: Barometer reading 29-500 ins., attached thermometer 40. On the line opposite to 40 and under 29-5 ins., is the correction -030 in. Therefore the reading corrected for temperature is 29-500 -030 = 29-470 ins. If the barometer reading be intermediate between any two given in the Table, the correction can easily be found by interpolation. (3) In comparing barometric observations made at different places, account must be taken of their respective heights above sea- level ; for the higher the station the lower will be the reading of the 1 Table I. has been extracted from Table II. in the Report of the Royal Society Committee of Physics, including Meteorology, on the Objects of Scientific Inquiry in those Sciences. London, 1840. BAROMETER 9 barometer. The height of the cistern of the barometer above sea-level must therefore be accurately ascertained, which is best done by levelling from the nearest Ordnance Bench Mark (/^), the height of which above sea-level will be found on the Ordnance map of the district. The correction for height above sea-level depends not only on the altitude, but also on the temperature and the pressure of the air. Table II. 1 (p. 46) gives the corrections for reducing the barometer readings to sea- level for every 10 feet up to 1000 feet, for each ten degrees of air temperature from 20 to 80, at the sea-level pressures of 28-0 ins., 29-0 ins., 30-0 ins., and 31-0 ins. From this Table another should be prepared for the height of the particular station for which it is to be used, giving the correction for altitude for every tenth of an inch pressure from 27-0 ins. to 31-0 ins., and each ten degrees of air temperature from 20 to 80. Table III. (p. 50) is a specimen for a station 190 feet above sea-level. This Table has to be thus con- structed : the form having been ruled, and the temperatures at the top, and the sea-level pressures in the left-hand column filled in, the corrections for 190 feet, at 28-0 ins., 29-0 ins., 30-0 ins. and 31-0 ins. are copied from Table II., and entered on the lines representing these values ; the intermediate readings are then filled up by interpolation that is, by equally apportioning the difference between the two sets of figures. When this has been done, it will be seen what is approximately the average correction in the present case it is -21 ; this may be taken as -2, and by deducting -2 from all the values in the left-hand column, and entering the results in the right-hand column, the reading at the station corresponding to that at the sea-level will be approximately obtained. This right-hand column is to be used for ascertaining the correction to be applied to the barometer reading to reduce it to sea-level ; in fact, after completing the Table, to prevent mistakes, the 'left-hand column had better be erased. The following Example will show the method of applying the foregoing corrections. Suppose the readings to be : Attached thermometer. Barometer. Dry-bulb. Correction for index error. 55 29.526 ins. 53 +-005 in. then ins. Barometer reading . . . . 29-526 ( i ) Correction for index error .... +-005 (2) Correction for temperature 55 (Table I.) . 29-461 (3) Correction for altitude 190 feet, 53 (Table III.) . +-206 Barometric pressure at sea-level . . . 29-667 1 Table II. has been compiled from Table II. in Instructions in the Use of Meteorological Instalments, issued by the Meteorological Office. London, 1885. io HINTS TO METEOROLOGICAL OBSERVERS When the correction for index error is the same throughout (as in the Fortin barometer) a Table may be prepared in which all three corrections are combined. This avoids the successive applica- tion of the several corrections, and saves much time and labour, besides greatly reducing the liability to mistake. It will be seen in Table III. that a change of 0-6 in. in the pressure produces the same amount of variation in the correction for altitude as is produced by an alteration of 10 in the temperature of the air. For instance, the correction for altitude when the pressure is at 30-0 ins., at the air temperature 50, is the same as that when the pressure is 29-4 ins. and the air temperature 40. So that taking, as regards the correction for temperature of the mercury, a mean reading of the barometer for the place of observation, this correction may be combined with that for altitude, including also the constant index error correction. Table V. (p. 52) is a specimen of this form of Table, made out for a station 190 feet above sea-level, for each 06 in. of barometer-reading from 28-60 ins. to 30-40 ins. and every two degrees of temperature of the dry-bulb and attached thermometers. To use the Table : Look in the right-hand or left- hand column of the Table on p. 5 2 for the reading of the barometer at the station, and carry the eye horizontally to the temperature of the air (i.e. dry-bulb thermometer reading), and then vertically downwards, and through the corresponding column in the second half of the Table on p. 53, to the value horizontally opposite the temperature of the attached thermometer, where will be found the required correction. The Table of combined corrections is intended only to be used for ordinary pressures and temperatures, as it is based upon average values. For extreme readings both of pressure and temperature the corrections should be worked out in detail from Tables I. and III. (4) In order to render barometrical observations in various parts of the world intercomparable, they must be so expressed that equal heights may denote exactly equal pressures. The force of gravity is not quite the same in all latitudes, and hence it neces- sitates a correction with reference to the latitude of the point of observation. The standard value of gravity adopted is that prevailing at latitude 45. Table IV. (p. 51) gives the corrections for each degree of latitude and for each half-inch of barometric pressure from 27 ins. to 3 I ins. Management. Barometers should be very carefully handled, so as to avoid breakage, or admission of air into the tube. It is best to carry the instrument with the cistern end upwards. If the barometer has to be sent away, it should be securely packed in a properly prepared box with rubber strips which grip the tube when the lid is closed. The THERMOMETERS 1 1 lid of the box should be fastened with screws, and not nailed down. The cistern end should be clearly marked on the lid. In the case of a Fortin barometer the mercury should be screwed up so as to fill the tube and cistern, before the instrument is taken down. Aneroid. The Royal Meteorological Society does not accept readings of aneroid barometers from its observers. It is found that these are not to be relied upon for long periods, because the metal of which their mechanism is constructed is not perfectly elastic, and does not return precisely to its normal condition after being subjected to change of strain under large variations of atmospheric pressure. However, the self-recording aneroids, of which many are now in use, yield records of considerable interest, and when frequently checked or controlled by the readings of a standard barometer (see p. 37) they are of value in showing the variations and extremes of pressure. It must be remembered that the aneroid readings correspond to readings of the mercurial barometer reduced to 32. Thermometers. The Maximum Thermometer may be on either Negretti and Zambra's, or on Phillips' principle. Negretti and Zambra's con- struction (Fig. 4) is as follows : The bore of the tube is reduced FIG. 4. Negretti and Zambra's Maximum Thermometer. in section near the bulb in such a way that whilst the expand- ing mercury forces itself into the tube, on contraction the column of mercury in the tube breaks off, so that its upper extremity shows the highest temperature that has been attained. The instru- ment is set by holding it bulb downwards and shaking it until the mercurial column becomes continuous throughout. It is to be mounted horizontally. Before reading, it is well to notice that the end of the column nearest the bulb has not run away from the point of contraction, through vibration or otherwise ; if it has, the thermometer should be tilted very gently until the detached column comes in contact with the contraction in the tube. In Phillips' construction (Fig. 5) the index is formed by a small portion of the mercurial column, separated from the main thread by a minute air-bubble ; this portion is pushed on before the column when the temperature rises, but does not return with it when it falls. The detached portion of the column therefore rests at the extreme position to which it has advanced, and the end of it farthest from J2 HINTS TO METEOROLOGICAL OBSERVERS the bulb registers the highest temperature which has been attained. The instrument is set by holding it bulb downwards and gently FIG. 5. Phillips' Maximum Thermometer. tapping the lower end so as to allow the detached portion of the mercury to approach the rest, from which it remains separated only by the air-bubble. This thermometer is also to be mounted horizontally. The Minimum Thermometer generally used is that known as Rutherford's (Fig. 6). The fluid employed is spirit, and in it there is immersed a pin or index. When the temperature falls, the surface of the spirit draws the index along with it ; but on rising again, the spirit passes the index, leaving it at the lowest point to which it has been drawn, the end farthest from the bulb thus FIG. 6. Minimum Thermometer. registering the minimum temperature. The instrument is set by raising the bulb and allowing the index to slide to the end of the column of spirit. The thermometer must be firmly fixed and mounted quite horizontally, so that the index may not be disturbed by vibration of the thermometer screen during wind. The Dry-bulb and Wet-bulb Thermometers (Fig. 7) should be precisely alike, and have small bulbs, which should be 3 or 4 inches apart. The wet -bulb should be covered with a single piece of very thin and soft muslin. For a cylindrical bulb this covering should take the form of a close-fitting sewn jacket. A conductor consisting of four strands of No. 12 darning cotton in the form of a noose should be tied round the neck of the bulb over the muslin, and led through a small orifice in the cover of a water receptacle, which should be placed an inch or so from the bulb, below and on the outer side of it. Care should be taken not to fasten the cotton too tightly round the neck of the bulb, or the circulation of the water along the strands will be THERMOMETERS 13 checked at this point. A conical glass cup with a copper lid having a small hole in it should be used, as glass vessels of other forms are liable to be broken during frost. Care must be taken to keep the cup filled with water. Clean rain, or distilled, water should be employed. The muslin and con- ducting thread should be washed in boiling water prior to use, and changed at least once a month, and more frequently if there is any appearance of dirt or deposit upon them. It is a good plan when rilling up the glass with water to pour some over the muslin, or to raise the water receptacle and immerse the bulb in the water so as to give the muslin- a bath, as by these means dust will be readily removed and the muslin kept clean. In damp weather the dry -bulb thermometer should be carefully wiped dry a few minutes before observation. When the temperature is below the freezing-point, the wet -bulb requires careful management. In- stead of a film of water round the bulb there must be a thin coating of ice, which can be produced by wetting the bulb with a camel's hair brush or by pouring a few drops of water over the muslin ; this must be done about an hour before the time of observation, as when the water is poured on the muslin the mercury will run up to 32 and remain there until the freezing process is com- plete, after which it will descend below that of the dry -bulb. The process of freezing may sometimes be accelerated by fanning the bulb. Immediately after a frost the water in the receptacle should be thawed, and the muslin and conductor wetted to restore proper action. Thermometer Screen. The thermometers above described must be mounted in the Stevenson Screen of the pattern approved by the Royal Meteoro- logical Society (Figs. 8 and 9). A free current of air can pass through the screen, and the sun cannot shine on the thermometers. The screen is a double louvred box, its internal dimensions being : length 1 8 inches, width 1 1 inches, and height 1 5 inches ; with a FIG. 7. Dry-bulb and Wet-bulb Thermometers. HINTS TO METEOROLOGICAL OBSERVERS double roof, the upper one projecting 2 inches beyond the sides of the screen all round, and sloping from front to back. The front is hinged as a door, and opens downwards (Fig. 8). The screen should be placed over short grass in a freely exposed situation, with the door opening to the north ; it is desirable that it should never be in the shade or within 10 feet of any wall, especially of one having a southerly aspect. It is to be mounted on four stout posts, and at such a height that the bulbs of the dry and wet ther- mometers shall be 4 feet above the ground. The posts should be buried from I 8 inches to 2 feet in the ground, and the soil carefully rammed down. In places exposed to much wind, it is also desirable to brace up the posts to prevent vibration of the screen. The thermo- meters should be sus- pended on uprights near the middle of the screen, the maximum and minimum being in front of the dry and wet, and arranged in such a way that the scales of the latter can be seen above the two former (Fig. 8). The screen must be painted white, the finish- ing coat being composed of white paint and copal varnish. It is desirable that the screen be repainted during the spring of each year. It will be a convenience to have a wooden rack placed on the grass immediately in front of the screen for the observer to stand on when reading the thermometers. Thermometer Shelter for Tropical Countries. The Stevenson Thermometer Screen is hardly suitable for use in tropical countries. It is therefore desirable for any one wishing to take temperature observations in such places to adopt the follow- ing arrangements recommended by the Committee of the British Association on the Climate of Tropical Africa : The Thermometers should be placed within an iron cage, which should at all times be kept locked, so as to prevent interference with the instruments. This cage should be suspended under a thatched shelter which should be situated in an open spot at some distance from buildings, must FIG. 8. FIG. 9. Royal Meteorological Society's pattern of Stevenson Thermometer Screen. THERMOMETERS 15 be well ventilated, and guard the instruments from being exposed to sunshine or rain. A simple hut, made of materials available on the spot, would answer this purpose. A gabled roof with broad eaves, the ridge of which runs from north to south, is fixed upon four posts, standing 4 feet apart. Two additional posts may be introduced to support the ends of the ridge beam. The roof, at each end, projects about 1 8 inches. In it are two ventilating holes. The tops of the posts are connected by bars or rails, and on a crossbar is suspended the iron cage with the thermometers. These will then be at a height of 6 feet above the ground. The gable ends may be permanently covered in with mats or louvre-work, not interfering with the free circulation of the air ; or the hut may be circular. The roof may be covered with palm-fronds, grass, or any other material locally used by the natives as building material. The floor should not be bare, but covered with grass or low shrubs. Care must be taken to fix the cage firmly, so that the maximum and minimum thermo- meters may not be disturbed by vibration. Reading's. The observations are made as follows : Having let down the door of the Stevenson Screen, the dry-bulb and wet-bulb thermometers are to be read first, so that they may not be affected by the nearness of the observer. The maximum thermometer is to be read next by noting the point at which the end of the column of mercury is lying. The minimum thermometer is read last, by noting the position of the end of the index farthest from the bulb. (The end of the column of spirit shows the temperature at the time of observation.) When this has been done, and the figures written in the observation book, the instruments should be looked at again to see that no mistake has been made in entering their readings. The maximum and minimum should then be set. When set, the end of the mercury in the maximum, and the end of the index farthest from the bulb in the minimum, should indicate nearly the same temperature as the dry-bulb. The muslin and cotton on the wet-bulb should be examined, and the glass cup filled with water, after which the door of the screen should be closed. All the thermometers should be read to tenths of degrees. This can readily be done by mentally dividing the space between each degree into ten parts and estimating at what tenth the end of the column or index stands. Terrestrial Radiation. For determining the intensity of terrestrial radiation a sensitive spirit minimum thermometer graduated on the stem, and without attached scale, should be used, and placed horizontally on short grass (Fig. 10). No blade of grass should ever be i6 HINTS TO METEOROLOGICAL OBSERVERS allowed to shade the bulb of the thermometer. When the ground is covered with snow the thermometer should be placed on FIG. 10. Grass Minimum Thermometer. | the surface of the snow instead of remaining buried underneath. It is desirable that the thermometer should be protected from being damaged or trodden upon. In order to secure this, a portion of the grass plot, 1 8 ins. long and 12 ins. wide, should be enclosed by fixing four stakes in the ground, one at each corner, and twisting a piece of wire round the top. The stakes should be about 8 ins. high. If the stakes and wire are painted white, they can easily be seen, and so will tend to keep anyone from treading on the thermometer. Earth Temperatures. The most convenient instrument for ascertaining the tempera- ture of the soil is that known as Symons's Earth Thermometer (Fig. 1 1 ). This consists of a sluggish ther- mometer mounted in a short, weighted stick attached to a strong chain, and of a stout iron pipe which is drawn out at the bottom to a point and driven into the earth to any required depth. The thermometer, the bulb of which is usually surrounded by a thick piece of india-rubber, is lowered into the tube and the top closed by a copper cap which should be thoroughly water-tight. Care must be taken to see that the india- rubber band does not swell too much, other- wise it may prevent the thermometer being lowered to the proper depth in the tube. If only one thermometer be used, the bulb should be lowered to the depth of I foot below the surface ; but if more than one be employed, the usual depths are 2 feet and 4 feet. The tubes should be inserted in the soil below short grass in a well-exposed position, and the portion of the tube above the soil (which should not exceed 6 inches) and also the cap should be painted white. FIG. ii. Symons's Earth When snow has fallen it should not be swept )n) " away from the ground round the earth ther- mometer, but left to melt in the same manner as the snow in the neighbourhood. THERMOMETERS Solar Radiation. The Black-bulb and Bright-bulb Thermometers in vacua may be used to furnish an estimate of the intensity of solar radiation. These consist of sensitive maximum thermo- meters, the former of which has the bulb and i inch of the stem coated with dull lamp black ; each thermometer is enclosed in a glass jacket, from which the air has been exhausted as com- pletely as possible. These instruments should be mounted on a post 4 feet above the ground (Fig. 12), with their bulbs directed to the south. These thermometers ought to be tested in sunshine at the National Physical Laboratory after enclosure in their vacuum jackets, as the corrections usually given on the certificate of verification apply merely to the thermometer before the blackening and enclosing in the outer jacket. Defects of Thermometers. FIG. 12. Black -bulb and Spirit thermometers are liable to a serious Bright-bulb Thermo- . r ., ,. r , r ii_ meters in vacua. defect, viz. the evaporation of a portion of the spirit from the column, and its condensation at the top of the tube. Extremely low temperatures at times reported as having been regis- tered at certain places, have been often traced to this fault, for thermometers may have as much as 5 or 10 of spirit lodged at the top of the tube. To correct this, hold the instrument bulb downwards with one finger steadying the tube, and swing it sharply. If this be not successful, the thermometer should be held in the right hand about a third of the way up from the bulb, and the upper part of the tube gently tapped on the palm of the left hand. This will usually dislodge the spirit and cause it to flow down the sides of the tube, but patience and perseverance are to be recommended in the operation. The thermometer must then be placed in an upright position for an hour or so, to allow all the spirit to run down the tube and join the column. As it is not always possible to see the spirit at the top, it is very desirable occasionally to place all the thermometers in a basin of water and after the lapse of an hour compare them together, first well stirring the water. With grass minimum thermometers it is a good plan to lay them on the grass with the scale downwards, as the enamel at the back will then act as a protection from the sun to the spirit in the tube and so render it less liable to get out of order. Some instrument makers supply minimum thermometers with the end of the tube buried in, or covered over with, a piece of wood. 18 HINTS TO METEOROLOGICAL OBSERVERS Such thermometers should not be used, as it is not possible to see whether any spirit has condensed at the top of the tube. Dry-bulb and wet -bulb thermometers are sometimes supplied with a piece of wood fastened across the lower part of their scales to hold the tubes in position ; and consequently when low tempera- tures occur this wood hides the end of the column of mercury, and so renders it impossible to get a reading of the thermometer. This piece of wood should be either cut through or removed entirely. Phillips' maximum thermometer is liable to get out of order by the air-bubble working back into the bulb, and consequently rendering the instrument an ordinary thermometer. This can usually be set right by placing the bulb in a mixture of salt and ice. When the mercury has fallen to its lowest point (nearly at zero), the thermo- meter should be taken out of the freezing mixture and held slightly inclined, bulb uppermost, so that a portion of the mercury may be detached from that in the bulb. When the mercury rises out of the bulb on increase of temperature, it will be found that the detached portion will be separated from the main column by a bubble of air. The divisions on the tubes of the thermometers should corre- spond with those on the attached scale. If they do not, the screws in the brass clips should be loosened and the tube readjusted and then wedged up by packing in pieces of cork. The black marking of the divisions on the thermometer tubes sometimes gets washed out, and the graduation consequently becomes indistinct. It may easily be restored by rubbing a little printer's ink, lamp-black and oil, or the point of a common black-lead pencil, along the tube, which should be perfectly dry. It is a good plan, when changing the muslin and cotton on the wet bulb, to rub the scales and tubes of all the thermometers with the old pieces before putting on the fresh ones, and then to wipe them with a dry duster. This will keep the scales clean. [If a black-lead pencil is at the same time rubbed over the divisions on the tubes, they will be made distinct and very easy to read.] Suspension of Thermometers. The brass plates for hanging the thermometers, which are screwed on to the back of the frames, should have a slot as well as a hole ; and when the thermometers are hung in the screen, the heads of the screws should be driven close to the slots to prevent the thermometers vibrating in windy weather. In places exposed to much wind it is sometimes desirable to keep the thermometers rigid by means of wooden buttons placed underneath. Thermometer Corrections. The corrections for the index errors of the different thermometers are given on the certificates of verification for every ten degrees from 12 to 92. The correction for the readings at the inter- HYGROMETRY 19 mediate parts of the scale can be readily found by equally ap- portioning the difference between the two sets of figures. Suppose the corrections to be as follows : 12 22 32 42 52 62 72 82 92 + 0-3 +02 o-o -o-i -o-i o-o -0-1 -0-3 -0-2 These should be apportioned thus : Below 17 +o-3 17 to 25 +0-2 25 to 29 +0-1 29 to 37 o -o 37 to 57 -o -i 57 to 67 o.o 67 to 75 -o-i 75 to 79 -0-2 79 to 87 -o .3 Above 87 -0-2 Hygrometry. From the readings of the dry-bulb and wet-bulb thermometers can be deduced the temperature of the Dew-point, the Elastic Force of Aqueous Vapour, and the Relative Humidity. Glaisher's Hygrometrical Tables are those in general use in this country. All deductions from observations of the dry-bulb and wet-bulb ther- mometers are open to some degree of doubt when near or below the freezing-point. Dew-point. By means of Table VI. (p. 54), based on Glaisher's factors, the Dew-point can be quickly calculated from the readings of the dry-bulb and wet-bulb thermometers. The arrangement of the Table is as follows : The columns on the left and right give the reading of the dry-bulb thermometer for every degree from 10 to 20 and from 30 to 100, and for every half degree from 20 to 30. The other columns give, for each degree of difference between the readings of the dry-bulb and wet-bulb thermometers, the amount to be subtracted from the reading of the wet-bulb thermometer to obtain the temperature of the dew-point The amount for tenths of degrees can be at once obtained by merely shifting the decimal point one place to the left The following examples will show the manner of using the Table : Example I. Suppose the reading of the dry-bulb ther- mometer to be . . . 5O-o And the reading of the wet-bulb thermometer to be 45-o The difference is . . 5-o On looking at the Table, we find opposite 50 and under 5-o, that the amount to be subtracted from the reading of the wet-bulb thermometer is . . . > S'3 Therefore the dew-point is, 45-o 53 . . . 39-7 Example 2. Suppose the reading of the dry- bulb ther- mometer to be . . . . 55-o And the reading of the wet-bulb thermometer to be '48- 3 The difference is . . . 6 -/ 20 HINTS TO METEOROLOGICAL OBSERVERS On referring to the Table, we see opposite 55 and under 6-o, that the amount to be subtracted is 5-8 ; for the remain- ing o-7, take the tenth part of the value standing opposite 55 and under 7-o, that is, the tenth part of 6 c -7, which is nearly o -/. The total amount to be subtracted from the reading of the wet-bulb thermometer is thus 5-8 + o-7 or . 6 -5 Therefore the dew-point is, 48-3 -6-5 . . . 4i-S Example 3. Suppose the reading of the dry-bulb ther- mometer to be . . . . 3 2 -5 And the reading of the wet-bulb thermometer to be 30 -8 The difference is . . i-7 In the Table opposite 32 and under i-o, we find 2-3, and under 7-o we find i6-2, the tenth part of which is i-6, or the total amount to be subtracted for 32 of dry-bulb ther- mometer, and difference i-7, is 3-9. Similarly the amount to be subtracted for 33 of dry- bulb thermometer, and difference i-7, is 3 -4 ; consequently, by interpolation, the amount to be subtracted for 32-5 of dry- bulb thermometer, and difference i-7, is . . 3-7 Therefore the dew-point is, 3 o- 8 3- 7 . . 27-! Elastic Force of Aqueous Vapour. The Elastic Force of Aqueous Vapour is dependent upon the temperature of the dew-point. Table VII. (p. 56) gives the elastic force for every tenth of a degree of temperature, from o-o to ioo-9, the whole degrees being given in the vertical columns headed o-o, ajid the tenths in the succeeding columns. Relative Humidity. This term is used to express the percentage of saturation of the air with aqueous vapour, and is calculated by dividing the elastic force of aqueous vapour at the temperature of the dew-point by that corresponding to the actual temperature of the air (i.e. the dry-bulb reading). Example: Dry-bulb 55-o, dew-point 46- 5 ; the Elastic Force cor- responding to these will be -433 in. and -317 in. respectively. There- fore, dividing the latter by the former, the result is 0-73 ; and taking Saturation as 100, the Relative Humidity will be 73, i.e. 73 per cent. In Table VIII. (p. 58) is given the Relative Humidity for every two degrees of temperature from 20 to 70, and also at 10, 75, 80, 90, and 1 00, and for every two-tenths of a degree of difference between the dry-bulb and wet-bulb readings from o-o to i8-o. This Table has been prepared according to the plan described in the Quarterly Journal of the Royal Meteorological Society, vol. vii. p. 2. The values contained therein may, however, occasionally differ from those obtained by the above method to the extent of I per cent. For temperatures below 10 the humidity may be worked out RAIN GAUGE 21 approximately by using the figures given at 10, as changes below that temperature are very slight. Similarly for temperatures a few degrees above 100 the same method may be followed by using the figures given at 100. To use the Table : Look in the column on the left or right for the nearest degree to the dry-bulb reading ; then carry the eye horizontally along until the column is reached corresponding to the difference between the readings of the dry-bulb and wet-bulb thermo- meters, when the Relative Humidity will be found. Intermediate readings can be interpolated in the usual way. Example: Dry-bulb 585, wet-bulb 5 i-;, the difference is 6-8. Having found 58 in the column on the left or right, run the eye along this line until the column under 6 -8 is reached, when the Relative Humidity will be found, viz. 62 per cent. When the differences between the dry-bulb and wet-bulb readings are greater than those given in Table VIII., the Relative Humidity may be worked out from the elastic force at the temperature of the dry-bulb and that at the dew-point in the manner described above. Rain Gauge. The Rain Gauge is best made of copper, and should have a circular funnel of either five or eight inches diameter, with a can and a bottle (roughly marked with half- inches) inside to collect the water. It is very desirable that it should be of the Snowdon pattern that is with a 6 in. cylinder on top of the funnel and a sharp brass rim (Fig. 1 3). It should be set in an open situation, away from trees, walls, and buildings at the very least, as many feet from their base as they are in height and it should be so firmly fixed that it cannot be blown over. The gauge should be planted in the earth and fixed by stakes or placed in a hole which exactly fits it in a block of cement. The top of FIG. 13. Rain Gauge (Snow- the rim should be one foot above the ground and must be kept quite level. The measurement of the rain is effected by pouring out the contents of the bottle into the glass measure, which must be placed quite vertical, and reading off the division to which the water rises ; the reading is to be taken midway between the two apparent surfaces of the water. The glass measure is usually graduated to represent tenths and hundredths of an inch, and holds 0-50 inch of rainfall. Each division represents the one-hundredth of an inch, the longer divisions five one-hundredths, and the long divisions, having figures attached, tenths of an inch. If there be more than half-an-inch of don pattern) and Measuring Glass. 22 HINTS TO METEOROLOGICAL OBSERVERS rain, two or more measurements must be made, and the amounts added together. The complete amount should always be written down before the water is thrown away. The gauge must be exa- mined daily at 9 a.m., and the rainfall, if any, entered to the previous day ; if none be found, a line or dots should be inserted in the register, instead of leaving the space blank or putting noughts. It is desirable that very heavy falls of rain should be measured immediately after their occurrence, entering the particulars in the remarks ; but taking care that the amount be included in the next ordinary registration. A fall recorded as o-oi in. or above is held to constitute a " rain day," or, to put it more accurately, a " day of precipitation." If the gauge contains less than one-hundredth (-01) of an inch, but more than half that amount, it should be entered as -01, while if there is less than half that amount the few drops may be thrown away and the day entered as if no rain had fallen. The measurements of rainfall should be entered in the register in hundredths of an inch that is, there should always be two figures to the right of the decimal point. If the amount is less than -10 in. the decimal point and the figure o must always be inserted in order to avoid uncertainty thus, -01, etc. Small amounts of water are at times deposited in the rain- gauge by dew, hoar frost, or fog. Whenever this occurs, the amount must be treated as rainfall and entered accordingly. When self-recording rain-gauges are used, care must be taken to fix them in such a position that the water, when emptied by the syphon or tipping-bucket, can run away, otherwise the instrument will not work properly owing to the excess of water round the outflow pipe. Snow. When snow falls, that which is collected in the funnel of the gauge is to be melted and measured as rain. This melting may be quickly done by adding to the snow a measured quantity of warm water, and afterwards deducting this quantity from the total measurement. If the snow has drifted, or if the funnel cannot hold all that has fallen, a section of the snow should be obtained in several places where it has not drifted, by inverting the funnel, turning it round, lifting and melting what is enclosed. The section should, if possible, be taken from the surface of a flat stone. Care must be taken that the section is of the snow that has fallen during the twenty-four hours, and does not include any previously fallen snow. A convenient method is to have a cylinder of the same diameter as the rain-gauge and of considerable depth, for use in snowy weather. It is also desirable to measure with a foot-rule the depth of snow in several places where it has not drifted, and to enter the same in the " Remarks " column. A foot of snow may be considered as roughly equivalent to an inch of rain, but the proportion varies considerably in different falls. PERCOLATION GAUGES 23 Evaporation. If practicable, an attempt should be made to determine the amount of evaporation. For this purpose it is desirable to have a galvanised iron tank four or six feet square, and two feet deep. This should be sunk in the ground, with the top level with the blades of the grass, and should be kept filled with water to within about three inches of the rim. The height of the water should be measured every day at 9 a.m. with a special measuring gauge reading to hundredths of an inch, such as Field's Hook gauge or Halliwell's Float gauge. The difference between the measurement on one day and the next will give the amount of evaporation. When rain has fallen, the amount, as shown by the rain-gauge, should be allowed for. Percolation Gauges. The amount of rain percolating into the ground may be ascer- tained by means of a water-tight tank filled with the earth of the locality. A convenient form of percolation gauge is one made of slate, and of a cubic yard in capacity, the upper edges being bevelled so as to leave the sharp edge inside the gauge. The top of the gauge should stand about two inches above the surface of the ground, and the gauge should be filled with earth to within two inches of the top. In some cases the ordinary turf of the district is laid on the top of the materials composing the percolation gauge the gauge itself representing an exact section of the strata of the district while in other cases the percolation gauges have no plants growing upon the surface. Gauges of this kind may be advantageously used in duplicate, one with the natural herbage of the district growing upon the surface, and the other without it. The water may be collected from the gauge by means of a drain or pipe at the bottom, and the collected water should be stored in a receptacle sufficiently large to hold not less than an equivalent of one inch of rain falling on the surface of the gauge. The quantity of water percolating can be measured in a graduated glass similar in principle to, but of larger capacity than, a rain-gauge glass. If very small quantities are required to be measured, and the percolation gauge is one yard square, the quantity may be measured in an 8-inch rain-gauge glass and divided by 26, when it will give the quantity passing through the percolation gauge. The quantity of water percolating into the ground in different years depends very much upon the period of the year in which the rain falls ; and as it is such rain as passes through the ground that furnishes the supply to the perennial springs of the country, these observations will afford a valuable record of the quantity of water which will be available in any district. Well Measurements. Neither rain nor percolation gauges really represent the storage of water which occurs in the ground. Well measurements, there- HINTS TO METEOROLOGICAL OBSERVERS fore, afford very valuable information as to the quantity of water which has passed into the ground from time to time, and is stored there for future use. In making such observations it is desirable to select a well as remote as possible from other wells, especially those where steam-power is employed for constant pumping. The measurement should be made from a fixed point at the mouth of the well to the water surface, as owing to the common practice of deepening wells in dry times, errors are likely to occur if the depth of water only is taken. The water surface should be referred to Ordnance datum. Such measurements should not be taken less frequently than once a week, but in critical periods of the state of the water, usually in the autumn, when the water begins to rise after a period of heavy rain, more frequent observations should be made, in order to determine the exact period when the rise begins. In selecting a well for observation, the more distant it is from a stream the better, as the underground water escaping into an adjoining stream so influences the level of the water in, such a well that the annual amount of fluctuation may be very small. On account of the difference in the fluctuation in various wells in the same district, observations in any well can be com- pared only with the same well and not with observations in other wells in the district, unless all the conditions with reference to the underground water of the district are known, and the differences in the fluctuation between various wells have been carefully compared. Wind Direction. The wind should be observed to sixteen points of the compass and capital letters should be entered in the register to indicate the directions, thus N North. NNE North-north-east. NE North-east. ENE East-north-east. E East. ESE East-south-east. SE South-east. SSE South-south-east. S South. SSW South-south-west. SW South-west. WSW West-south-west. W West. WNW West-north-west. NW North-west. NNW North-north-west. FIG. 14. Points of the Compass. The Direction of the Wind (which should be the " true " direction and not the " magnetic ") may be ascertained from the indication of a freely moving vane ; when such is not available, by observing the drift of smoke. By the direction of the wind is meant WIND that point of the compass from which it is blowing. Care must be taken by watching the vane for a few minutes to see that the direction is that of the general current of air passing over the place, and that the air current is not affected by local circumstances. It is , desirable to fix astronomically one cardinal point, and frequently to examine the position of the pointers of the vane (a pole carrying a vane is liable to twist owing to changes of humidity). This should be either the North point by means of the pole star, or the South point by means of the Sun, employing one of the following methods : The pole star, Polaris, is practically due North at the following times : In January and July February August March ,, September April October May ,, November June ,, December at 6 a.m. and 6 p.m. 4 ,, 2 Noon 10 a.m. 8 4 , 2 , Midnight. , 10 p.m. To determine when the Sun is due South, refer if possible to a good local sun-dial ; when the dial shows 1 2 h. om. the sun is due south. If this cannot be done, proceed as follows : For any station situated in England, Wales, or Scotland, ascertain its longitude in time from the map on p. 26 (Fig. 15). Then obtain (from the nearest reliable railway station or postal telegraph office clock) the correct Greenwich time, and set a watch by adding the correction for longitude (which is 4 minutes of time for each degree of longitude) to the Greenwich time for places in east longitude, and subtracting it for places in west longitude. This gives Local time. Then apply a further correction for the Equation of Time, the amount of which may be taken to the nearest minute for the given day from the accompanying table, interpolating for intermediate days : Jan. i siibtract 4 min. 55 1 ,, 21 12 Feb. i 14 ii 14 21 14 Mar. i 12 5, ii 10 21 7 Apr. I 4 ,5 ii i ,, 21 ac Id i . May I add 3 mi 55 II 4 21 4 June i 2 55 II I ,, 21 sub ract 2 July i 4 55 II 5 ,, 21 6 Aug. i 6 55 II 5 ,, 21 3 Sep. i ac id o mil 5, II 4 21 Oct. i 7 10 55 II 13 21 Nov. i 15 16 55 II 16 ,, 21 Dec. i 14 1 1 55 II 6 5, 21 2 A watch thus set gives Local apparent time, such as would be shown by a properly adjusted sun-dial, and when the watch so adjusted indicates i 2h. om. the sun will be due south. Example. Let the instant at which the sun is south at Penzance on February 21 be required. Penzance is west of Greenwich 5^- = 22 minutes, to be subtracted from Greenwich or Railway time. And 26 HINTS TO METEOROLOGICAL OBSERVERS the Equation of Time on February 21 is 14 minutes, also to be sub- tracted. The total amount to be subtracted is therefore 36 minutes. If, on the day the watch is to be adjusted, the railway clock shows I oh. 2om., the watch must be set to gh. 44m. Then at I2h. om. by the watch the sun will be due south. For stations in Ireland the longitude must be reckoned from Dublin, as railway clocks in Ireland show Dublin 'time, which is 25 minutes after Greenwich time. 2Y/IST O* EAST 2 4.' FIG. 15. Approximate Westerly Variation of the Magnetic Needle, over the British Isles, 1912. The true North point may be determined also by means of an azimuth compass, remembering that in the British Isles the magnetic north lies to the west of the true north, or the true north is east of the magnetic north. The amount of variation over the British Isles, which ranges from 15 to 21, may be taken from the map (Fig. 15), which will serve for several years to come. Roughly speaking, in the British Isles a north and south line lies along the line NNE-SSW by compass. Wind Force. The Force of the Wind should be estimated according to Beau- fort's scale. The following are the values, with the equivalent velocities in miles per hour, as recently adopted by the Meteorological Office : Calm 1 Light Air 2 Light Breeze . . . 3 Gentle ,, 4 Moderate ,, . . . 5 Fresh ,, . . '. .. 6 Strong ,, 7 High Wind (Moderate Gale) 8 Gale .... 9 Strong Gale . % . 10 Whole 11 Storm .... 12 Hurricane WIND Equivalent velocity 27 y o miles per hour. 1-3 4-7 8-12 13-18 19-24 25-31 32-38 39-46 47-54 55-63 64-75 above 75 In the Dines' Pressure- tube Anemometer advantage is taken of the fact that the air in blowing over an obstacle produces small 1 I ,3 FIG. 1 6. The " Head" of the Dines' Pressure-tube Anemometer. FIG. 17. Recording Instrument. differences of pressure on various sides of the obstacle, which are capable of exact measurement, and afford information of the velocity of the wind. The " head " consists of a piece of tube open at one end, which end is kept facing the wind by a vane (Fig. 16). The wind blowing into the tube produces an excess of pressure within it. There is also a piece of tube placed vertically, and pierced by a ring of small holes. The wind blowing over these holes produces a slight decrease of pressure inside. These differences of pressure are com- municated by composition tubing, which may be of any length, to the place where the recording or indicating part of the instrument is placed. In the self-recording form of the instrument (Fig. 17) the registration is produced by means of a bell-shaped vessel which floats inverted in water in a closed chamber. The pressure-tube, i.e. the tube coming from the " head " in which there is an excess of 28 HINTS TO METEOROLOGICAL OBSERVERS pressure, opens above the water-level inside the inverted floating vessel, and the other tube, i.e. that in which there is a decrease of pressure, communicates with the sealed chamber. Very trifling differences of pressure are sufficient to alter the level at which the inverted vessel floats, and a pen rigidly attached to this vessel makes a continuous record on a clock drum in the usual way. This instru- ment will register very light winds, down perhaps' to I or 2 miles per hour, and is convenient, because being once erected, the " head " requires cleaning about once a year and very little attention of any other kind. A good exposure, however, is essential. If placed on an ordinary house the "head" should be quite 30 ft. above the ridge of the roof. If a Robinson Anemometer (Fig. 1 8) be used, it should be mounted on a pole in a fully exposed situation, so as to be inter- FIG. 1 8. Robinson Anemometer. fered with as little as possible by buildings, trees, etc. The bearings should always be kept well oiled. It should be remembered that the graduations on these instruments have been calculated on the supposition that the velocity of the wind is three times that of the motion of revolution of the cups, but recent experiments have shown that this value is too high, and varies also with the size of the instrument. For the Robinson Anemometer known as the " Kew pattern " the dimensions of which are : distance of centre of cups from centre of axle 24 inches, and diameter of cups 9 inches the correct factor (provided the instrument is in perfect working order) is very close to 2-2. For smaller instruments distance of centre of cups from centre of axle 1 8 inches, and diameter of cups 6 inches the factor is 2-8. The following particulars should always be given as to a Robinson anemometer: i. Length of arm (axis to centre of cup). 2. Diameter of cups. 3. How the registration is effected (mechani- SUNSHINE RECORDERS 29 5. Height cally, electrically, or otherwise). 4. Name of maker, above general surface of the ground. Sunshine Recorders. The instrument generally adopted for recording the duration of Sunshine is the Campbell-Stokes Sunshine Recorder. This consists of a sphere of crown glass 4 inches in diameter and 3 Ibs. in weight, supported on a pedestal in a metal zodiacal frame (Fig. 19). It must be fixed in such a position that the sun can shine on the instrument the whole of the time it is above the horizon, a condition sometimes difficult to fulfil, but experience will soon indicate the best and most acces- sible spot where the recorder can be placed. The points requiring FlG I9 ._ Ca mpbell-Stokes Sunshin^ Recorder.. attention in the setting up of the instrument are that it shall be placed level as regards east and west, that the axis of the frame shall be inclined to the horizon by an angle equal to the latitude of the place, and that the image of the sun,, when the sun is due south, shall fall on the meridian line marked on the frame,, to which the noon hour line on the card is adjusted. The sunshine record is thus in hours of Local apparent time (such as is shown by a sun-dial), which it is con- venient to use for sunshine observations in order to facilitate their discussion. To determine when the sun is due south see in- structions under the sec- tion Wind Direction (p. 25). It would be well to make more than one deter- FiG. 20. Section of Frame. FIG. 21. Showing the . . position of the trace on mmation of the meridional the cards according to pos ition, SO as to ensure the time of year. the accurate setting of the instrument. A prepared card being inserted in the proper groove (Fig. 20), according to the season of the year, the sun when shining burns away or chars the surface at the points on which its image 30 HINTS TO METEOROLOGICAL OBSERVERS successively falls, and so gives a record of the duration of bright sunshine. The spot of light must be at its proper position on the card, which may be determined by reference to Fig. 21, and the burnt trace must run parallel with the line on the card. The card should be removed after sunset (even if it has not been scored), and a new one inserted ready for the following day. Each card should be carefully dated, and the day of the week also written thereon. The straight or equinoctial cards are to be used from March I to April 1 2, and again from September I to October I 2. The long curved or summer cards are to be used from April 1 3 to August 3 1 , and the short curved or winter cards from October 13 to February 28 or 29. The ends of the card projecting above the FIG. 22. Campbell-Stokes Sunshine Recorder, universal pattern, with adjustment for latitude. horizontal top of the frame should be cut off, so as not to intercept the sun's rays near sunrise and sunset. A simple test for ascertaining whether the glass ball is in the centre of the frame is to pass a sovereign round between the ball and the card. If the sovereign can be passed round uniformly, the ball may be assumed to be in the centre of the frame ; but if it sticks at any point, the instrument requires adjustment. This can be done by loosening the screw of the pedestal at the back of the slate slab, and moving the pedestal until the ball is quite in the centre of the frame. The screw should then be carefully tightened. When the instrument has been properly adjusted it should not be disturbed, but should be firmly fixed either by cement or in some other way. Fig. 22 shows the "universal pattern" of the Campbell-Stokes CLOUDS 31 Sunshine Recorder in which the frame is adjustable to any latitude. In this instrument the ball is kept in position by two clamping- screws. Care must be taken to see that the ball is exactly midway between the top and bottom ends of the frame, otherwise if it is too high or too low the sunshine trace will not run parallel with the card. In time of snow, when there is any possibility of sunshine, the snow should be removed from the ball and from between the ball and the card. Hoar frost should also be removed from the ball as soon as possible ; and the ball should always be kept clean. A chamois leather or a soft cloth should be used for this purpose. Another form of Sunshine Recorder is the Jordan Photographic Recorder. In this instrument the record depends upon the intensity of the actinic rays, and is therefore not directly comparable with the record from a Campbell-Stokes Recorder, which depends upon the burning power of the sunshine. The sunshine should be measured in hours and tenths of an hour, and not in minutes. A " sunless day " is that on which the record of sunshine is less than three minutes. Ozone. The amount of Ozone present in the atmosphere is sometimes made the object of observation. There are, however, great difficulties in the way of accurately observing the ozone of the atmosphere, the test-papers employed being frequently unreliable. Therefore the determination of ozone is not now included by the Royal Meteorological Society in its scheme of ordinary observations. Clouds. The proportion of sky covered with cloud is to be observed. This is done by estimation, the scale adopted being o to 10; o in- dicating a cloudless sky, 5 half clear and half clouds, and 10 a sky which is covered with cloud or overcast. It is also desirable to note the kind of cloud prevalent at the time, and the direction from which it is moving. The different modifications and forms of cloud, as originally given by Luke Howard, were Cirrus, Cirro-cumulus, Cirro-stratus, Cumulus, Cumulo-stratus, Stratus, and Nimbus. It is desirable, however, to employ the nomenclature adopted by the International Meteorological Committee, and published in the International Cloud Atlas, which is as follows : I. CIRRUS (Ci.). Detached clouds of delicate and fibrous appearance, often showing a feather-like structure, generally of a whitish colour. Cirrus clouds take the most varied shapes, such as isolated tufts, thin filaments on a blue sky, threads spreading out in the form of feathers, curved filaments ending in tufts, sometimes called Cirrus untinus, etc. They are sometimes arranged in parallel belts which cross a portion of the sky in a great circle, and by an effect of perspective appear to converge towards a point on the horizon, or if sufficiently 32 HINTS TO METEOROLOGICAL OBSERVERS extended, towards the opposite point also. (Ci.-St. and Ci.-Cu. are sometimes arranged in similar bands.) 2. CIRRO-STRATUS (Ci.-St.). A thin, whitish sheet of clouds sometimes covering the sky completely and giving it only a milky appearance (it is then called Cirro-nebula), at other times presenting more or less distinctly a formation like a tangled web. This sheet often produces halos around the sun and moon. 3. CiRRO-CUMULUS (Ci.-Cu.). Mackerel Sky. Small globular masses or white flakes without shadows, or showing very slight shadows, arranged in groups and often in lines. 4. ALTO-STRATUS (A.-St). A thick sheet of a grey or bluish colour, sometimes forming a compact mass of dark grey colour and fibrous structure. At other times the sheet is thin, resembling thick Ci.-St., and through it the sun or the moon may be seen dimly gleaming as through ground glass. This form exhibits all changes peculiar to Ci.-St. but from measurements its average altitude is found to be about one-half that of Ci.-St. 5. ALTO -CUMULUS (A.-Cu.). GREAT WAVES. Largish globular, masses, white or greyish, partially shaded, arranged in groups or lines, and often so closely packed that their edges appear confused. The detached masses are generally larger and more compact (resembling St.-Cu.) at the centre of the group, but the thickness of the layer varies. At times the masses spread themselves out and assume trie appearance of small waves or thin slightly curved plates. At the margin they form into finer flakes (resembling Ci.-Cu.). They often spread themselves out in lines in one or two directions. 6. STRATO - CUMULUS (St.-Cu.). Large globular masses or rolls of dark clouds often covering the whole sky, especially in winter. Generally St.-Cu. presents the appearance of a grey layer irregularly broken up into masses of which the edge is often formed of smaller masses, often of wavy appearance resembling A. - Cu. Sometimes this cloud-form presents the characteristic appearance of great rolls, arranged in parallel lines and pressed close up against one another. In their centres these rolls are of a dark colour. Blue sky may be seen through the intervening spaces which are of a much lighter colour [" Roll-Cumulus " in England, " Wulst-Cumulus " in Germany]. St.-Cu. clouds may be distinguished from Nb. by their globular or rolled appearance, and by the fact that they are not generally associated with rain. 7. NIMBUS (Nb.). RAIN-CLOUDS. A thick layer of dark clouds, without shape and with ragged edges from which steady rain or snow usually falls. Through the openings in these clouds an upper layer of Ci.-St. or A.-St. may be seen almost invariably. If a layer of Nb. separates up in a strong wind into shreds, or if small loose clouds are visible floating underneath a large Nb. the cloud may be described as Fracto Nimbus (Fr.-Nb.). [" Scud " of sailors.] 8. CUMULUS (Cu.). WOOL-PACK CLOUDS. Thick clouds of which the upper surface is dome-shaped and exhibits protuberances while the base is horizontal. These clouds appear to be formed by a diurnal ascensional movement which is almost noticeable. When the cloud is opposite the sun, the surfaces facing the observer have a greater brilliance than the margins of the protuberances ; when the light falls aslant, as is usually the case, these clouds throw deep shadows ; when, on the contrary, the clouds are on the same side of the observer as the sun, they appear dark with bright edges. True Cumulus has well-defined upper and lower limits, but in strong winds a broken cloud resembling Cumulus is often seen in which the detached portions undergo continual change. This form may be distinguished by the name of Fracto-Cumulus (Fr.-Cu.). 9. CUMULO-NIMBUS (Cu.-Nb.). THE THUNDER-CLOUD ; SHOWER-CLOUD. Heavy masses of cloud rising in the form of mountains, turrets, or anvils, generally surmounted by a sheet or screen of fibrous appearance ("false Cirrus") and having its base a mass of cloud similar to Nimbus. From the base local showers of rain or snow (occasionally of hail or soft hail) usually fall. Sometimes the upper edges assume the compact form of cumulus, and form massive peaks CLOUDS 33 round which delicate " false Cirrus " floats. At other times the edges themselves separate into a fringe of filaments similar to Cirrus clouds. This last form is particularly common in spring showers. The front of thunder-clouds of wide extent frequently presents the form of a large arc spread over a portion of a uniformly brighter sky. 10. STRATUS (St.). A uniform layer of cloud resembling a fog, but not resting on the ground. When this sheet is broken up into irregular shreds in a wind, or by the summits of mountains, it may be distinguished by the name Fracto-Stratus (Fr.-St.). The Frontispiece gives illustrations of various cloud forms, with their names and approximate altitudes. This has been reproduced by permission from Mr. R. Inwards' Weather Lore, 3rd edition, 1898. The kind of cloud should be indicated by the initial letters of the name of the cloud as follows : Ci. Cirrus. Ci.-St. Cirro-stratus. Ci.-Cu. Cirro-cumulus. A.-St. Alto-stratus. A.-Cu. Alto-cumulus. St.-Cu. Strato-cumulus. Nb. Nimbus. Cu. Cumulus. Cu.-Nb. Cumulo-nimbus. St. Stratus. Fr.-Cu. Fracto-cumulus. Fr.-Nb. Fracto-nimbus. Fr.-St. Fracto-stratus. St.-cf. Stratus-cumuliformis. Nb.-cf. Nimbus-cumuliformis. M.-Cu. Mammato-cumulus. A cloud mirror or nephoscope is sometimes used for observing the direction of movement of the clouds, and ascertaining their apparent rate of motion. Observers who are able to devote time to the study of the clouds should pay attention to the following points and enter the same in the register : (1) The kind of cloud. Indicated by the international abbreviations of the name of the cloud, as given above. (2) The direction from which the cloud comes. By remaining perfectly still for several seconds the motion of clouds may be observed easily against a steeple or pole erected in an open space. If the motion of the cloud be very slow the head should be steadied by using a rest. This method of observing must be applied only to clouds near the zenith ; in the case of clouds near the horizon perspective may lead to errors. In such cases a nephoscope or Mr. Besson's harrow should be used, and the instructions issued with these instruments should be followed. These two observations are the most important. In addition, we may note, if there be opportunity (3) The point of radiation of the upper clouds. These clouds often take the form of narrow parallel lines, which, by reason of perspective, appear to converge towards a given point on the horizon. The " point of radiation " is the name given to the point where these belts or their prolongation meet the horizon. This point should be indicated in the same manner as the direction of the wind, N., N.N.E., etc. (4) Undulated clouds. It often happens that the clouds have the appearance of regular parallel and equidistant stripes like waves on the surface of water. This occurs most frequently with Cirro-cumulus, Strato-cumulus (roll Cumulus), etc. It is important to note the direction of these stripes. When two distinct systems are apparent, as is often the case with clouds separated into^ globular C 34 HINTS TO METEOROLOGICAL OBSERVERS masses by stripes in two directions, the direction of both systems should be noted. As far as possible these observations should be confined to stripes near the zenith, so as to avoid errors caused by perspective. (5) The density and situation of a bank of Cirius. The upper clouds often assume the form of a tangled web or sheet which, as it appears above the horizon, looks like a thin bank of a light or greyish colour. As this form of cloud is closely connected with barometrical depressions, it is desirable to observe (a) the density (for which the following scale is suggested : o = very thin and irregular ; I = thin but regular ; 2 = fairly thick ; 3 = thick ; and 4 = very thick and of a dark colour) ; and () the direction in which the sheet or bank appears thickest. (6) Remarks. All interesting particulars should be noted, such as (a) During summer all low clouds tend to assume forms resembling cumulus. In such cases an entry should be made in the column for " Remarks " Stratus or Nimbus cumuliformis. () At times a cloud may present a mammillated lower surface. This appearance should be noted under the name of Mammato-cumulus. (c] The ovoid form with sharp edges assumed by certain clouds, particularly during the occurrence of sirocco, mistral, or fohn, should be designated lenticularis ; for example, Cumulus -lenticularis, Stratus-lenticularis (Cu.-lent.). (St.-lent). Such clouds frequently show iridescence, (d) A note should always be made of the fact when clouds seem to be stationary or in very rapid motion. Weather. In addition to the foregoing observations, it is very desirable to note the state of the weather and any phenomena that may have occurred since the last observation, such as Thunderstorms, Halos, Fog, Snow, Hail, etc. These may be entered in the register in an abbreviated form by the letters of Beaufort's notation, or by the International symbols, as follows : BEAUFORT'S LETTERS AND INTERNATIONAL SYMBOLS. Aurora \U j Ice Crystals -> ! Snow on Ground [*] b Blue Sky | 1 Lightning < Soft Hail A c Clouds (detached) Lunar Corona vl; Solar Corona O w Dew r/s- I Lunar Halo (JJ \ Solar Halo d Drizzling Rain m Mist Dust Haze oo ! o Overcast (dull) f Fog EE p Passing Showers Gale / r Rain Glazed Frost ~ ! Rainbow g Gloomy Silver Thaw h Hail A I s Snow Hoar Frost *_ ] Snow Drift , q Squally t Thunder Thunderstorm u Ugly (threatening) v Visibility e Wet air The intensity of any individual phenomenon may be distinguished by the figures of o and 2, which should be used as exponents of the symbols, so that o should indicate slight, and 2 strong, e.g. A = slight hail, 4 2 = heavy hail. Hours of Observation. At the Second Order Stations the hours of observation are 9 a.m. and 9 p.m. local time, which hours should be adhered to punctually. The maximum and minimum thermometers are to be read and set at 9 p.m., and the readings entered to the day on which they are observed. REGISTER 35 At the Climatological and other Stations the observations are required to be made once each day, viz. at 9 a.m. local time. The reading of the maximum thermometer and the rainfall are to be entered to the previous day, but the reading of the minimum thermometer is to be entered to the day on which it is taken. If possible, observations should also be taken at 3 p.m. These should at least include readings of the dry-bulb and wet-bulb thermometers and the amount of cloud. The maximum and minimum thermometers must not, however, be interfered with at that time. At some stations observations are taken at 6 p.m. for newspaper reports or municipal purposes. When such is the case care must be taken not to impair the rainfall and maximum and minimum tem- perature records for the ordinary meteorological day. Note-Book. All the original observations should be written down at the time they are made in a properly ruled or printed note-book (not on loose slips of paper), so that they may be available for reference in case any question should arise about them afterwards. It is a very convenient plan to put an elastic band over each end of the note- book, as by that means it can be opened at once at the proper place, and in wet weather the other leaves will not be wetted by rain, or the figures smudged. If a lead pencil be tied to the note-book with a piece of string it will always be at hand for entering the observations. Omissions must be carefully avoided, otherwise true means cannot be obtained : it is, therefore, necessary to have a well-trained deputy to take the observations in the absence of the usual observer. Lamp. When observations are taken after dark it is desirable to have a good and efficient lamp, which should always be kept well trimmed. Matches should on no account be used. An electric lamp is con- venient for reading thermometers, as it is always ready and gives out no perceptible heat. Register. In entering the observations in the register it is absolutely essential that they be correctly copied from the original note-book ; it is most desirable, therefore, that the entries be afterwards checked by reading against the originals. In filling in the barometer readings, the whole inches may be omitted when there are several of the same number together, except the first and the last. In no other case, however, should any figure be omitted in any column, even though it be a cypher, as it may thereby cause an error in the adding up. In taking the means, the work of addition may be much simplified by adopting some number as constant or common. For instance in 3 6 HINTS TO METEOROLOGICAL OBSERVERS the barometer column it will be readily seen which is the prevalent number, 29 or 30 ins. ; if 29 be taken as the constant, it will be necessary only to add up the figures to the right of the decimal point, and then add I in. to this total for every inch above 29, and deduct I in. for every inch below. Example: If the total of the figures to the right of the decimal amount to 21-648, and to the left of the decimal 30 ins. occur 7 times, and 28 ins. 3 times, the other values being 29 ins. ; then, by adding 7 for the 30 ins. and deducting 3 for the 2 8 ins., we get the following results : 7 3=4 + 21-648 = 25-648 ins. This would, therefore, be the total for the barometer column, taking 29 ins. as the constant. Dividing this total by 31, which we will presume to be the number of days in the month, and adding 29 ins., the mean will be 29-827 ins. In the same way constants may be employed in adding up the dry, wet, maximum, and minimum thermometers and other columns. Great care should be taken to make the addition correct ; it is therefore desirable that the columns be added twice, first upwards and then downwards ; so that if a mistake be made one way, it will most probably be found out the other way. In dividing the sums to obtain the means, the last figure should always be increased by one if the remainder be one-half or more of the divisor. The mean temperature of the month for the stations of the Royal Meteorological Society is determined by adding together the mean maximum and the mean minimum, and dividing the sum by 2. Example: Mean maximum, 63-4, mean minimum, 46- 2 = iO9-6. This divided by 2 gives 54-8. The extreme range of temperature for the month is the difference between the absolute maximum and minimum readings. The mean range of temperature for the month is the difference between the mean maximum and mean minimum readings. When the mean of the 9 a.m. and 9 p.m. observations of the amount of cloud is less than 2-0, this is called a Day of Clear Sky, but when the mean is above 8-0 it is called an Overcast Day. When during any part of the day the force of the wind is 8 and above (on the Beaufort scale) this is counted as a day with Gale. Previous to 1911 force 7 was counted as a Gale, but the International Meteorological Committee has recently decided that the minimum value for a Gale should be raised to force 8. In summarizing the observations of the direction of the wind, these should be taken out to eight points of the compass. If the wind has been observed to sixteen points, the intermediate points must be split up and apportioned to each side, e.g. 3 NNE will become i N and 2 NE 6 SSE 3 SE 3 S 1 1 WSW 5 SW 6 W In the " Remarks " column the special features of the day should SELF-RECORDING INSTRUMENTS 37 be noted, and any particular phenomena with the time of their occurrence. At the end of each month a brief account of the chief characteristics of the weather should also be given, with indication of their effects upon agriculture, health, etc, A specimen of a Climatological Return is given on p. 65. Self-Recording 1 Instruments. Much interesting and valuable information may be obtained from self -recording barometers, thermometers, hygrometers, and rain gauges. These are of great service in measuring the time, duration, intensity, and various phases of phenomena. A brief description of this class of instruments is as follows : THERMOGRAPH. The thermometer consists of a very thin curved metal case (a Bourdon tube) containing alcohol, one end being a fixture and the other movable. As the alcohol expands or contracts with the changes of temperature it alters the curvature of the tube, FIG. 23. Thermograph. making it flatter or otherwise. In another form the tube is replaced by a bimetallic spiral. The end of the tube communicates its motion by means of a metal rod to a lever carrying a pen, which marks a graduated paper wound on the cylinder. A clock turns the cylinder round once in seven days (Fig. 23). DRY-BULB AND WET-BULB THERMOGRAPH. This consists of a pair of thermometers, which are placed side by side ; but they are curved reversely, and are placed as far apart as possible. The wet- bulb thermometer is covered with muslin, and is kept moist by a water vessel below, into which the muslin dips, and also by a capillary siphon from a second water vessel above. BAROGRAPH. This instrument consists of a series of vacuum boxes by which the effects of variation of the atmospheric pressure are increased and transmitted by a system of levers to an arm carrying a pen (Fig. 24). HAIR HYGROGRAPH. The actuating portion is a wisp of about 38 HINTS TO METEOROLOGICAL OBSERVERS a dozen hairs fastened at each end, and stretched laterally by a small weighted lever ; the elongation and contraction of the hairs causes motion of the lever, and is thereby recorded on the cylinder. FIG. 24. Barograph. SELF-RECORDING RAIN GAUGE. There are several patterns of self-recording rain gauges, e.g. Beckley's, Halliwell's, Casella's, and Negretti & Zambra's, etc., which give excellent results in careful hands. The two principal types of self-recording rain gauges are the float pattern and the tipping bucket pattern. In the former the rain is collected in a reservoir in which there is a float carrying a pen, and as the float rises a trace is marked on the chart showing the rate at which the rain fell. In the tipping bucket pattern, the rain is collected in a small tilting bucket divided into two equal parts, which tip over alternately when -01 in. has fallen. A level- carrying a pen is thus raised by means of an escapement wheel, and a trace resembling a series of steps is recorded on the chart. The method of recording is practically the same in each of the above instruments, so the following directions for use will be applicable to all. First remove the pen from the chart by means of the lever at the base, then unscrew the thumb screw in the centre of the drum and lift the latter off the steel rod, and wind the clock. The brass band which holds the chart in position should be removed and a new chart placed on the cylinder, which should then be replaced on the steel rod, care being taken to see that the small wheel underneath gears into the large one. The cylinder should be turned round until the pen is in a line with the correct day and hour on the chart. The pen should then be refilled with ink and the lever turned to the left to bring the pen into contact with the chart. It is advisable to move the pen slightly to ensure a proper flow of ink. PHENOLOGICAL OBSERVATIONS 39 Additional Observations. The conditions prevailing in the upper atmosphere may be investigated by the use of suitable kites such as the Hargreave or the Dines box kites with a meteorograph attached. At the Blue Hill Observatory, U.S.A., records have been obtained at a height of 3 miles by means of kites. Small pilot balloons may be sent up for determining the drift of the upper currents. If the circumstances permit, a balloon carrying a very light Dines meteorograph should be sent up on the first Thursday of each month and the other days appointed by the International Aero- nautical Committee. Such balloons sometimes reach an altitude of as much as 16 miles above the earth's surface. On the occurrence of any exceptional phenomena, e.g. floods, whirlwinds, showers of dust, damage by lightning, hail, etc., steps should be taken at once to gather accurate information respecting the same, which should be carefully entered in the register. In the case of floods an effort should be made to have a permanent mark cut in a wall or on the pier of a bridge, recording the height and the date of the flood. It is also desirable that photographs of meteorological phenomena should be taken whenever possible, and copies of these should be forwarded to the Royal Meteorological Society for preservation as a permanent record. Much valuable information may be obtained from observa- tions on the number of dust particles in the air by means of Aitken's Dust Counter, and also from analyses of air in different districts. Phonological Observations. A careful watch should be kept for the first flowering of uncultivated plants, the arrival and song of birds, the appearance of butterflies and other insects, etc. The Royal Meteorological Society is always glad to receive such observations. The following is the list recommended for observations : PLANTS. 1. Hazel (Cory lus Avellana). 2. Coltsfoot (Tussilago Farfara). 3. Wood Anemone (Anemone nemo- rosa). 4. Blackthorn (Prunus spinosa). 5. Garlic Hedge Mustard (Sisym- brium Alliaria). 6. Horse Chestnut (sEsculus Hippo- castanum}. 7. Hawthorn (Cratcegus Oxyacantha). 8. White Ox Eye (Chrysanthemum Leucanthemum). 9. Dog Rose (Rosa canina). i o. Black Knapweed ( Centaurea nigrd}. 1 1 . Harebell (Campanula rotundifolid). 12. Greater Bindweed (Convolvulus septum}. 13. Ivy (Hedera Helix}. The same individual trees and shrubs should be observed each 40 HINTS TO METEOROLOGICAL OBSERVERS year, and as regards herbaceous plants, those growing in precisely the same spots this is of the greatest importance. In the case of trees and shrubs they must be of mature growth. The particular plants selected for observation should be situated neither in very sheltered nor, on the other hand, in very exposed positions, and should neither be abnormally early nor late in their flowering for the district. When from any cause any of the selected plants cease to be available, other specimens of the same variety similarly situated should be observed instead of them. A plant is to be considered " in flower " when the stamens of the first blossom on it first become visible. As soon as the date of one plant has been secured, watch for the appearance of the next on the list. If, unfortunately, the first flowering be missed by a day or two, the estimated date of first flowering should be given and an asterisk placed against the entry. Should the plant be estimated to have been in flower more than four days, no entry at all should be made. BIRDS. 14. Song Thrush (Turdus musicus}, first heard. 15. Swallow (Hirundo rustica}, first seen. 1 6. Cuckoo (Cuculus canorus}, first heard. 17. Nightingale (Daulias luscinia), first heard. 1 8. Flycatcher (Muscicapa grisold}, first seen. 19. Swallow (Hirundo rusticd), last seen. The date on which the note of the Song Thrush is first heard after January ist should be given. It must not be mistaken for that of the Missel Thrush. The notes of the Missel Thrush are less musical and connected, the strain is altogether much shorter, and, being repeated many times in succession, it wants the variety of that of the Song Thrush. The Swallow may be distinguished from the House Martin and Sand Martin by its back being of a uniform glossy steel-blue, almost black, by its long forked tail, and by the dingy white colour of its lower parts. The House Martin has the rump and lower parts pure white, while the Sand Martin is of a mouse colour above. The Swift differs from the Swallow in its more rapid flight, the peculiar narrow- ness of its outspread wings, and its general sooty colour. The observer should be certain that it is the Nightingale that is heard, as the Song Thrush also often sings late in the evening. The Flycatcher is a little greyish-brown bird, fond of sitting on a post, rail, or perch, whence it can readily dart off and seize a fly, usually returning at once to its former station. BOOKS AND PUBLICATIONS ON METEOROLOGY 41 INSECTS. 20. Honey Bee (Apis mellifica), first seen. 2 1 . Wasp ( Vespa vulgaris], first seen. 22. Small White Butterfly (Pieris rapes), first seen. 23. Orange-tip Butterfly (Anthocaris cardamines}, first seen. 24. Meadow-brown Butterfly (Epine- phile Janira), first seen. Books and Publications on Meteorology. The following is a brief list of works on meteorological subjects which observers may consult with advantage : ABERCROMBY, Hon. R. Weather. A Popular Exposition of the Nature of Weather Changes from Day to Day. 8vo. 1887. 5 s - ALLINGHAM, W. A Manual of Marine Meteorology. 8vo. 1900. 33. 6d. Barometer Manual for the Use ot Seamen. Published by the Meteorological Office. 8vo. 6th edition. 1909. 3d. BARTHOLOMEW'S Atlas of Meteorology. Folio. 1899. 523. 6d. Bulletin of the Mount Weather Observatory (U.S.). 8vo. CLAYDEN, A. W. Cloud Studies. 8vo. 1905. 125. Climatological Atlas of India. Published under the direction of Sir John Eliot. Folio. 1906. 365. Daily Weather Reports of the Meteorological Office. 4to. Subscription 53. per quarter. DAVIS, W. M. Elementary Meteorology. 8vo. 1894. ics. DEXTER, E. G. Weather Influences. 8vo. 1904. 8s. 6d. DICKSON, H. N. Meteorology. The Elements of Weather and Climate. 8vo. 1893. 2s. 6d. FERREL, W. A Popular Treatise on the Winds. 8vo. 1889. i6s. GLAISHER, J. Hygrometrical Tables adapted to the use of the Dry- and Wet- bulb Thermometer. 8vo. 2s. 6d. HANN, J. Lehrbuch der Meteorologie. 8vo. 2nd edition. 1906. 245. HANN, J. Handbuch der Klimatologie. 8vo. 3rd edition. 1908-11. HANN, J. Handbook of Climatology. Translated by R. de C. Ward. 8vo. 1903. I2s. 6d. International Catalogue of Scientific Literature. F. Meteorology. Published annually. 8vo. 155. International Cloud Atlas. 4to. 1896. i6s. International Meteorological Tables. 4to. 1890. 283. INWARDS, R. Weather Lore. A Collection of Proverbs, Sayings, and Rules concerning the Weather. 3rd edition. 8vo. 1898. 42 HINTS TO METEOROLOGICAL OBSERVERS Journal of the Scottish Meteorological Society. 8vo. Published annually. I2s. 6d. LEY, Rev. W. CLEMENT. Cloudland. A Study on the Structure and Characters of Clouds. 8vo. 1894. 73. 6d. MARRIOTT, W. Some Facts about the Weather. 8vo. 2nd edition. 1909. 6d. Meteorological Office. The Observer's Handbook. 8vo. Published annually. 35. Meteorological Record. Monthly Results of Observations made at the Stations of the Royal Meteorological Society. 8vo. Published quarterly, is. 6d. Meteorologische Zeitschrift. 4to. Published monthly. Annual subscription 2os. MILL, H. R. British Rainfall. 8vo. Published annually. IDS. Monthly Weather Review (U.S.). 4to. MOORE, Sir J. W. Meteorology, Practical and Applied. 8vo. 2nd edition. 1910. i os. 6d. MOORE, WILLIS L. Descriptive Meteorology. 8vo. 1910. 125. 6d. PERNTER, J. M., and EXNER, F. M. Meteorologische Optik. 8vo. 1910. Quarterly Journal of the Royal Meteorological Society. 8vo. 55. SCOTT, R. H. Weather Charts and Storm Warnings. 8vo. 3rd edition. 1887. SCOTT, R. H. Elementary Meteorology. 8vo. 6th edition. 1893. 5 s - SHAW, W. N., and LEMPFERT, R. G. K. The Life History of Surface Air Currents. 4to. 1906. 75. 6d. Smithsonian Meteorological Tables. 3rd edition. 8vo. 1907. Symons's Meteorological Magazine, edited by Dr. H. R. Mill. 8vo. Published monthly. 4d. WALDO, F. Modern Meteorology. 8vo. 1893. WALDO, F. Elementary Meteorology. 8vo. 1896. WARD, R. de C. Practical Exercises in Elementary Meteorology. 8vo. 1899. WARD, R. de C. Climate considered especially in relation to Man. 8vo. 1908. 6s. Weekly Weather Reports of the Meteorological Office. 4to. Annual subscrip- tion (which includes the Monthly Weather Report) 303. English and Metrical Scales. As the observations from foreign countries are made according to the metrical scales, it is convenient to be able to readily convert the English values into the metrical. Five tables for this purpose are given on pages 61-64. Meteorological Terms. The International Meteorological Congress held at Rome in 1879 expressed the opinion that an "International Dictionary of METEOROLOGICAL TERMS 43 Meteorology " should be published. As a step towards the carrying out of this Resolution, a " Glossary of Meteorological Terms " has been prepared and will be found on p. 66. The name of the person to whom it is believed the term is due and the date of its first use are given in square brackets. The author desires to acknowledge the assistance which he has received in the preparation of this Glossary from Members of the Council of the Royal Meteorological Society, and also from Bartholomew's Atlas of Meteorology and other sources. 44 HINTS TO METEOROLOGICAL OBSERVERS TABLE I. CORRECTIONS TO BE APPLIED TO BAROMETERS WITH Brass Scales EXTENDING FROM THE CISTERN TO THE TOP OF THE MERCURIAL COLUMN TO REDUCE THE OBSERVATIONS TO 32 FAHRENHEIT. Attached Thermometer. READING OF BAROMETER. Attached Thermometer. Ins. 27-0 Ins. 27'5 Ins. 28-0 Ins. 28-5 Ins. 29-0 Ins. 29'5 Ins. 30-0 Ins. 30-5 Ins. 31'0 20 + 021 + 021 + 021 + 022 + 022 + 023 + 023 + 023 + 024 20 21 018 019 019 019 020 020 020 02 1 021 21 22 016 016 016 017 017 017 018 018 018 22 23 013 014 014 014 014 015 015 015 015 23 24 Oil Oil Oil 012 OI2 OI2 OI2 OI2 013 24 25 009 009 009 009 009 009 009 OIO OIO 2 5 26 006 006 006 006 OO7 007 007 007 007 26 27 004 004 004 OO4 004 004 004 004 004 27 28 + 001 + 001 + -OOI + 001 + -OOI + 001 + -OOI + -OOI + 001 28 29 -OOI - 'OOI -OOI -OOI -OOI -OOI -OOI -OOI -OOI 29 30 004 004 004 004 004 004 004 004 004 30 31 006 006 006 006 007 007 007 007 007 31 32 008 009 009 009 009 009 009 OIO OIO 32 33 Oil Oil Oil 012 OI2 OI2 OI2 OI2 OI2 33 34 013 014 014 OI4 014 015 015 015 015 34 35 016 016 016 017 017 017 018 018 018 35 36 018 019 019 OI9 020 O2O 020 021 02 1 36 37 021 021 021 022 O22 022 023 023 024 37 38 023 023 024 024 O25 025 026 026 026 38 39 025 026 026 027 027 028 028 029 029 39 40 028 028 O29 O29 030 030 031 031 032 40 41 030 031 .031 .032 033 033 034 034 035 41 42 33 033 034 034 035 036 036 037 037 42 43 035 036 036 037 038 038 039 040 040 43 44 037 038 039 040 040 041 042 042 043 44 45 040 041 041 042 043 044 044 045 046 45 46 042 043 044 045 045 046 047 048 049 46 47 045 046 046 047 048 049 050 051 051 47 48 047 048 049 050 051 052 052 053 054 48 49 050 050 051 052 053 054 055 056 057 49 50 052 053 054 055 056 057 058 059 060 50 51 054 055 056 057 058 059 060 06 1 062 51 52 057 058 059 060 06 1 062 063 064 065 52 53 059 060 06 1 06 3 064 065 066 067 068 53 54 062 063 064 065 066 06 7 068 070 071 54 55 064 065 066 068 06 9 070 071 072 073 55 56 066 068 069 070 071 073 074 075 076 56 57 069 070 071 073 074 075 076 078 079 57 58 071 073 074 075 077 7 8 079 08 1 082 58 59 074 075 076 078 079 080 082 083 085 59 60 - -076 -.077 -079 -080 -082 -.08 3 -085 -086 -087 60 BAROMETER CORRECTIONS FOR TEMPERATURE 45 TABLE I. CORRECTIONS TO BE APPLIED TO BAROMETERS WITH Brass Scales EXTENDING FROM THE CISTERN TO THE TOP OF THE MERCURIAL COLUMN TO REDUCE THE OBSERVATIONS TO 32 FAHRENHEIT. Continued. Attached Thermometer. READING OF BAROMETER. Attached Thermometer. Ins. 27'0 Ins. 27'5 Ins. 28-0 Ins. 28'5 in, 29-0 Ins. 29'5 Ins. 30-0 Ins. 30-5 Ins. 31'0 60 -076 -077 -079 -080 -082 -083 -.085 -086 -087 60 61 078 080 08 1 083 084 086 087 089 090 61 62 08 1 082 084 085 087 088 090 091 093 62 63 083 085 086 088 089 091 093 094 096 63 64 086 087 089 090 092 094 095 097 098 64 65 088 090 091 093 095 096 098 100 101 65 66 090 092 094 096 097 099 101 102 104 66 67 093 095 096 098 100 102 103 105 107 67 68 095 097 099 IOI IO2 104 106 108 109 68 69 098 IOO IOI 103 105 107 109 IIO 112 69 70 100 102 104 106 108 109 in 113 115 70 71 IO2 104 106 108 no 112 114 116 118 71 72 105 107 109 in "3 115 117 119 i 20 72 73 107 109 in ii3 115 117 119 121 123 73 74 IIO 112 114 116 118 120 122 124 126 74 75 112 114 116 118 I2O 122 125 127 129 75 76 114 117 119 121 123 125 127 129 131 76 77 117 II 9 121 123 126 128 I 3 .132 134 77 78 119 122 124 126 128 I 3 133 135 137 78 79 122 124 126 128 131 133 135 137 140 79 80 124 126 129 131 133 136 138 I4O 143 80 Si 126 129 131 134 136 138 141 143 145 81 82 129 I3 1 134 136 138 141 143 146 148 82 83 131 134 136 139 141 143 146 I 4 8 I5 1 83 84 134 136 139 141 144 146 149 151 i54 84 85 136 139 141 144 146 149 151 154 156 85 86 138 141 144 146 149 '5 1 154 156 159 86 87 141 143 I 4 6 149 151 154 157 159 162 87 88 143 146 149 151 154 i57 159 l62 165 88 89 -I 4 6 148 151 154 156 i59 162 165 167 89 90 I 4 8 151 J53 I 5 6 159 162 164 I6 7 170 90 91 92 I 5 !53 III 156 158 159 161 l62 164 165 167 I6 7 170 170 172 i73 i75 91 92 93 155 158 161 164 167 170 172 175 178 93 94 157 161 163 166 .169 172 175 177 180 94 95 96 160 162 163 165 166 168 169 171 172 174 i75 178 I 7 8 181 180 183 183 185 i 97 165 168 171 174 177 180 183 186 188 98 167 170 173 176 179 183 186 188 191 98 99 169 J 73 176 179 182 185 188 191 194 99 100 -172 -175 -.178 -181 -184 -188 -191 -194 -197 100 4 6 HINTS TO METEOROLOGICAL OBSERVERS TABLE II. CORRECTIONS FOR REDUCING OBSERVATIONS OF THE BAROMETER TO SEA-LEVEL. 4 '53 BAROMETER AT SEA-LEVEL, 28'0 INCHES BAROMETER AT SEA-LEVEL, 29*0 INCHES 1 Temperature of External Air. Temperature of External Air. 20 30 40 50 60 70 80 20 30 40 50 60 70 80 Feet In. In. In. In. In. In. In. In. In. In. In. In. In. In. Feet. 10 Oil Oil OIO OIO OIO OIO 009 OI2 OI2 Oil Oil Oil Oil OIO 10 20 022 022 021 020 020 019 019 023 022 022 021 02 1 021 020 20 30 033 032 031 030 030 029 029 034 033 033 032 031 031 030 30 40 -044 043 042 041 040 039 038 045 044 044 043 042 041 040 40 50 055 054 053 051 050 049 048 057 056 055 053 052 051 050 50 60 066 064 063 06 1 060 059 058 068 067 066 064 063 061 060 60 70 077 075 073 071 070 068 067 079 078 076 074 073 071 070 70 80 088 086 084 082 080 078 077 091 089 08 7 085 083 08 1 080 80 90 098 096 094 092 090 088 087 102 IOO 098 096 094 092 090 90 IOO 109 107 104 IO2 IOO 098 096 3 III 108 106 104 102 IOO IOO 1 10 I2O 117 115 . II3 III 108 106 125 122 119 117 115 112 110 I1O 1 20 * I 3 I 128 125 123 121 118 116 136 133 130 127 I2 5 122 I2O 120 130 142 139 136 131 128 125 147 144 141 138 135 132 130 130 140 153 149 146 143 141 138 135 >I 59 155 '52 149 146 143 140 140 150 164 160 157 154 '^S 1 148 145 170 166 163 160 157 153 150 J 5o 1 60 175 171 168 164 161 157 154 181 177 174 170 167 I6 3 160 1 60 170 186 182 -178 174 171 167 164 192 188 184 181 177 173 170 170 180 197 193 189 I8 5 181 177 174 204 199 195 191 188 I8 3 179 180 190 208 203 199 195 191 187 183 215 210 206 202 -198 193 189 190 200 219 214 209 205 2OI 197 193 226 221 217 212 208 20 3 199 200 210 230 225 220 215 211 206 202 238 233 228 223 219 2I 4 209 210 220 241 235 230 225 221 216 212 249 244 238 233 229 224 219 22O 230 251 246 241 2 3 6 2 3 I 226 222 260 255 249 244 239 234 229 230 240 262 256 251 2 4 6 241 236 2 3 I 272 266 260 254 249 244 239 240 250 273 267 261 2 5 6 251 246 241 283 277 271 26 S 260 254 249 250 260 284 278 272 266 26l 255 250 294 288 281 275 270 264 259 260 270 295 288 282 276 271 265 200 305 299 292 286 280 274 269 270 280 306 299 293 287 28l 275 270 317 310 303 297 291 285 279 280 290 3*7 310 303 297 2 9 I 285 279 328 321 3H 307 301 295 289 290 300 328 320 313 307 301 295 289 339 332 325 318 312 305 299 300 310 339 331 324 317 -3II 304 298 351 343 335 328 322 315 309 310 320 35 342 334 327 321 314 307 362 354 346 339 332 325 318 320 330 360 352 344 337 331 324 317 373 365 357 349 342 335 328 330 340 37i 363 355 348 341 334 327 384 376 367 360 353 345 338 340 350 382 373 365 358 351 343 336 396 387 378 370 363 355 348 350 360 392 384 376 368 361 353 346 407 398 389 381 373 365 358 300 370 403 394 386 378 371 363 355 418 409 400 392 384 376 368 370 380 414 405 396 388 381 373 365 429 420 411 402 394 386 378 380 390 400 436 416 426 407 398 408 390 400 382 392 374 384 440 43 1 442 422 432 413 423 404 415 396 406 388 398 390 400 410 446 437 427 418 4IO 402 393 462 453 443 434 425 416 407 410 420 457 447 438 429 420 411 402 473 464 454 444 435 426 417 42O 430 468 458 448 439 43 421 412 485 475 464 455 445 436 427 430 440 479 468 458 449 440 431 422 496 486 475 465 455 446 437 440 45 490 479 469 459 450 440 43 1 507 497 486 476 466 45 6 447 450 460 5oi 490 479 469 460 450 44 1 519 508 497 486 476 466 457 4 60 470 512 501 490 479 469 459 450 530 508 497 486 476 466 470 480 522 511 500 489 479 469 460 529 518 507 497 486 476 480 490 533 521 510 499 489 479 470 552 540 529 518 507 496 486 490 500 544 532 521 5io 499 489 479 563 540 528 517 506 496 500 BAROMETER CORRECTIONS FOR ALTITUDE 47- TABLE II. CORRECTIONS FOR REDUCING OBSERVATIONS OF THE BAROMETER TO SEA- LEVEL. Continued. '5; BAROMETER AT SEA-LEVEL, 30'0 INCHES. BAROMETER AT SEA-LEVEL, 31'0 INCHES. M U) '53 ffi Temperature of External Air. Temperature of External Air. 20 30 40 50 60 70 80 20 30 40 50 60 70 80 Feet. In. In. In. In. In. In. In. In. In. In. In. In. In. In. Feet. 10 OI2 OI2 Oil on Oil Oil OIO OI2 OI2 Oil Oil Oil Oil OIO 10 20 023 023 023 022 022 021 021 024 024 023 022 022 022 02 1 20 30 035 034 034 033 032 032 031 036 036 035 034 033 033 032 30 40 047 046 045 044 043 042 041 048 048 047 045 044 044 042 40 50 059 058 056 055 054 053 052 060 000 059 057 056 055 053 50 60 070 069 068 066 065 06 3 062 072 071 070 068 067 066 064 60 70 082 08 1 078 077 076 074 072 084 08 3 08 1 079 078 077 075 70 80 094 092 090 088 086 084 082 096 095 093 090 089 087 085 80 90 105 104 -101 099 097 095 093 108 107 104 102 101 098 096 90 100 117 'US 112 110 108 105 103 I2O 119 US 113 112 108 106 100 1 10 I2 9 126 123 121 119 116 "3 132 130 127 124 123 119 117 1 10 120 140 138 134 132 129 126 124 144 .142 139 136 134 130 128 1 20 130 IS 2 149 146 143 140 137 i34 157 154 147 145 141 138 130 140 164 161 157 151 147 144 I6 9 166 162 I 5 8 156 152 149 140 150 I 7 6 172 168 las 162 158 155 182 178 173 I6 9 I6 7 163 160 150 160 I8 7 183 179 176 172 168 165 194 190 185 181 I 7 8 174 170 1 60 170 199 195 190 187 183 179 175 206 202 196 192 I8 9 185 181 170 1 80 211 206 202 198 194 189 185 218 214 208 203 2OO 195 191 180 190 222 218 213 209 204 200 196 230 226 220 215 211 206 202 190 200 234 229 224 220 215 2IO 206 242 237 231 226 222 217 212 200 2IO 246 240 235 231 226 221 216 254 249 243 237 233 228 223 210 220 257 252 246 242 236 231 227 266 26l 254 249 244 239 234 22O 230 269 263 257 253 247 242 237 278 273 265 260 255 250 245 2 3 240 28l 275 269 264 258 252 248 290 285 277 271 266 261 256 240 250 2)3 286 280 275 269 263 258 .302 297 289 283 277 271 266 250 260 304 297 291 285 279 273 268 314 308 300 294 288 282 277 260 270 316 309 302 296 290 284 278 327 319 312 306 299 293 287 270 280 328 320 3H 37 301 294 288 339 331 324 317 310 304 298 280 290 339 332 325 318 3" 305 299 351 343 336 329 321 309 290 3OO 351 343 336 329 322 315 309 363 354 347 340 332 : 326 319 300 310 363 354 347 340 333 326 3i9 375 366 359 352 343 337 330 3 IO 320 374 366 358 35 1 343 336 329 387 378 370 363 354 347 340 320 330 386 377 369 362 354 347 340 399 389 381 374 365 358 351 330 340 397 389 380 373 365 357 350 411 401 393 386 377 369 36l 340 350 409 400 392 384 376 368 360 423 413 405 397 388 380 372 350 360 421 411 403 394 386 378 370 435 425 417 408 399 391 382 360 370 432 423 414 405 397 389 380 447 437 428 419 410 402 393 370 380 444 434 425 416 408 399 391 459 449 439 43 421 .413 .404 3 80 390 455 446 436 427 418 410 401 471 461 451 441 432 424 414 390 4OO 467 457 447 438 429 420 411 483 473 462 452 443 434 424 4OO 410 479 468 458 449 .440 43 421 495 .484 473 463 454 445 435 4IO 420 49 480 469 460 450 441 431 507 .496 485 475 465 45 6 446 42O 430 502 491 480 470 461 451 442 519 57 .496 486 476 466 456 430 440 513 502 491 481 471 462 452 531 519 508 497 487 477 467 440 450 525 503 492 482 472 462 543 531 520 59 498 488 478 45 460 537 525 514 503 493 482 472 555 542 531 520 509 498 488 460 470 548 536 525 53 493 482 566 554 543 531 520 509 498 470 480 560 547 536 524 503 493 578 565 554 542 531 520 509 480 490 571 559 547 535 524 514 503 590 577 565 553 542 531 519 490 500 583 570 558 546 535 524 602 589 576 564 553 542 530 500 HINTS TO METEOROLOGICAL OBSERVERS TABLE II. CORRECTIONS FOR REDUCING OBSERVATIONS OF THE BAROMETER TO SEA-LEVEL. Continued. I BAROMETER AT SEA-LEVEL, 28*0 INCHES. BAROMETER AT SEA-LEVEL, 29*0 INCHES. ^ 'C Temperature of External Air. Temperature of External Air. 20 30 40 50 60 70 80 20 30 40 50 60 70 80 Feet. In. In. In. In. In. In. In. In. In. In. In. In. In. In. Feet. 510 554 542 531 520 509 498 488 574 562 550 538 527 516 506 5IO 520 565 553 541 530 519 -508 -498 -586 573 -561 549 537 -526 -516 520 530 -576 564 552 540 -528 517 507 597 -584 572 559 547 536 526 530 540 587 574 562 550 538 527 517 608 595 -582 570 546 536 540 550 597 584 572 560 548 537 527 619 -606 593 58o 568 556 546 550 560 608 595 582 570 558 547 536 630 616 603 590 578 566 555 56o 570 619 -605 592 - 5 8o - 5 68 545 641 -627 614 -60 1 -588 576 565 580 630 616 603 590 577 566 555 652 638 -625 611 -598 586 575 58o 590 641 627 -613 -600 -587 575 564 663 649 635 -621 -608 596 585 600 652 637 623 610 597 585 574 675 -660 646 632 619 -606 594 600 610 662 648 634 620 -607 595 583 -686 -671 657 643 629 -616 604 610 620 673 658 644 630 617 604 592 697 -682 -667 653 639 -626 -6 I4 620 630 683 -668 654 640 -627 614 -602 708 693 -678 663 -649 636 -624 630 640 694 679 -665 650 636 623 611 -719 -704 689 674 659 646 633 640 650 705 690 675 660 -646 633 -621 730 714 699 -684 -669 656 643 650 660 .716 700 685 670 656 643 -631 741 725 709 694 680 666 653 660 670 -726 710 695 680 -666 653 640 752 736 720 705 -690 -676 663 670 680 737 721 705 -690 676 -662 649 763 747 731 715 -700 -686 673 680 690 748 732 -716 700 -686 -672 659 774 758 742 -726 -710 -696 683 690 700 759 742 726 710 695 -68 1 -668 -786 -769 752 736 720 -706 -692 700 710 769 752 736 720 705 -691 677 797 -780 763 -746 730 716 702 710 720 -780 763 746 730 715 -701 687 -808 -791 774 757 -741 -726 .712 720 730 790 773 756 740 725 710 -696 819 80! 784 -767 751 736 721 730 740 -801 784 767 751 735 -720 -706 -830 812 795 778 -761 -746 731 740 750 812 794 777 761 745 730 716 -841 823 -805 .788 -771 756 -741 750 760 822 804 -787 -771 755 739 725 852 833 815 798 -781 -766 751 760 770 833 -815 797 -781 765 749 734 863 844 -826 -808 -791 776 -761 770 780 843 -825 -807 791 775 759 744 874 855 836 -818 801 -786 -770 780 790 800 854 865 ill 818 828 801 811 784 794 -768 778 753 -762 -885 -896 -866 877 847 -858 829 -840 811 -822 796 -806 -780 790 790 800 810 875 856 838 -821 804 -787 772 907 -888 -868 850 832 816 800 810 820 -886 867 -848 831 814 797 -781 -918 -898 -879 860 842 826 -809 820 830 897 877 858 -840 823 806 -790 -929 -909 -889 -870 852 836 -819 830 840 908 -888 868 850 833 816 800 -940 920 900 -88 1 -862 -846 829 840 850 -919 -898 -878 860 -842 -825 -809 95 ! 930 910 -891 -872 855 -838 850 860 929 -908 -888 870 852 835 818 -962 941 920 -901 -882 865 -848 860 870 940 919 899 -880 -862 845 -828 973 952 931 -912 892 875 -858 870 880 950 929 909 -890 -871 854 837 -984 -962 -941 -922 -902 885 867 880 890 -961 -940 919 -900 881 -864 -846 995 952 932 -912 -895 877 890 900 972 95 929 910 -891 874 856 006 984 963 943 923 905 -887 900 910 -982 -961 940 920 -901 883 -865 017 995 973 953 933 915 -896 910 920 993 -971 950 930 -911 -892 874 028 i -006 984 964 943 925 -906 920 930 1-004 -982 -960 -940 920 -902 884 039 1-017 994 974 953 935 916 930 940 1-014 992 -970 95 930 911 893 050 1-028 1-005 985 -964 945 925 940 950 1-025 1-002 980 960 940 -921 902 -061 1-039 1-016 995 974 955 935 95 960 1-035 I-OI3 991 970 949 930 -912 072 1-049 1-026 1-005 984 -965 945 960 970 1-045 I-O23 I-OOI 980 959 940 -921 083 i -060 1-036 1-015 994 974 954 970 980 1-056 1-033 I-OII 990 969 949 930 094 1-071 1-047 1-026 1-004 984 -964 980 990 1-067 1-044 I -02 1 I-OOO *979 959 940 105 i -08 1 1-057 1-036 1-014 994 974 990 IOOO 1-077 1-054 1-031 1-009 988 -968 949 -116 1-092 1-068 1-046 1-024 1-004 983 000 j BAROMETER CORRECTIONS FOR ALTITUDE 49 TABLE II. CORRECTIONS FOR REDUCING OBSERVATIONS OF THE BAROMETER TO SEA-LEVEL. Continued. w BAROMETER AT SEA-LEVEL, 30'0 INCHES. BAROMETER AT SEA-LEVEL, 31*0 INCHES. ,] .bfl Temperature of External Air. Temperature of External Air. 20 30 40 50 60 70 80 20 30 40 50 60 70 80 Feet. In. I In. .1. In. In. In. In. In. In. In. i In. In. In. In. In. Feet. 5io 594 -581 -569 557 545 534 523 614 -600 587 575 563 552 540 5 10 520 -606 593 -580 -568 556 545 533 -626 -612 599 587 574 563 551 520 530 540 550 -617 629 640 604 -615 626 591 -602 613 IS 600 -566 577 587 555 565 575 544 564 638 650 -662 624 -636 -648 611 -622 633 598 -609 620 -585 -596 -607 574 584 595 -562 572 583 530 540 550 5 6o -652 -638 624 611 598 -586 574 674 -660 645 632 618 605 593 *J S*J 56o 570 -663 -649 635 622 -608 -596 584 685 -671 -656 643 629 616 -604 57o 5 8o 590 600 675 -686 698 -660 -672 683 -646 -657 668 -632 643 654 619 629 640 -606 617 -627 595 -605 615 697 709 -721 -682 694 -706 -667 679 -691 654 -665 -676 639 650 -661 -626 637 -647 614 -625 635 580 590 600 610 .709 694 679 -665 650 637 625 732 717 -702 -687 -672 658 -646 610 620 -721 705 690 675 -66 1 -648 635 744 -729 713 -698 683 669 -656 620 630 732 -717 -701 -686 671 -658 -645 756 -741 724 -709 694 680 -667 630 640 744 -728 -712 697 682 -668 655 -768 736 -720 705 -691 -678 640 650 755 739 723 -708 692 679 -666 -780 -764 747 731 715 -701 -688 650 660 767 750 734 -718 703 689 676 792 -776 759 742 -726 712 699 660 670 778 -761 745 729 713 699 -686 804 -787 770 753 737 722 709 670 680 790 773 756 -740 -724 -709 -696 816 799 -782 -764 748 733 719 680 690 -801 784 -767 750 734 -720 -706 -828 810 793 775 759 744 730 690 700 813 795 -778 -761 745 730 -716 840 -822 804 -786 770 755 740 700 710 -824 -806 789 772 755 -740 -726 -852 833 815 797 -780 765 750 710 720 -836 -817 800 -782 -766 751 736 -864 845 -827 791 776 761 720 730 847 829 -811 793 776 -761 -746 -876 857 839 820 802 787 771 730 740 859 840 822 804 787 -771 756 -888 -868 -850 831 813 797 -781 740 750 870 -851 833 815 797 -782 -767 899 -879 -86 1 842 824 -808 792 750 760 -881 -862 843 825 -808 792 777 910 -890 -871 853 834 818 -802 760 770 893 873 854 836 818 -802 787 -922 902 -882 -864 845 829 813 770 780 904 -885 865 -847 829 -812 797 934 -914 893 -875 -856 839 823 780 790 916 -896 876 857 839 823 -807 946 926 905 -886 -867 850 834 790 800 -927 -907 887 -868 850 833 -817 958 938 -917 -897 -878 86 1 845 800 810 938 918 898 -878 -860 843 -827 -969 949 928 -908 -888 871 -855 810 820 950 929 909 -889 -871 854 837 -981 -960 939 -919 899 881 -865 820 830 -961 -940 920 -900 -88 1 -864 847 993 972 951 93 910 -892 875 830 840 973 951 931 911 -892 874 857 1-005 983 962 -941 -921 903 -886 840 850 984 -962 -942 922 -902 -885 867 1-017 995 973 952 932 -914 897 850 860 995 974 952 932 913 -895 877 1-028 i -006 984 963 943 -924 -907 860 870 1-007 -985 963 943 923 905 -887 1-040 018 - 99 6 975 955 935 -917 870 880 1-018 -996 974 954 934 915 897 1-052 029 1-007 -986 -966 946 927 880 890 1-030 1-007 -985 964 944 926 -907 1-064 041 1-018 997 -976 956 937 890 900 1-041 1-018 -996 975 955 936 -917 1-076 052 1-029 1-008 987 -967 948 900 910 1-052 1-029 1-007 -986 965 .946 927 1-088 063 1-040 1-019 998 -978 958 910 920 1-064 1-040 1-018 996 -976 956 937 I-IOO 075 1-052 1-030 1-009 989 969 920 930 1-075 1-051 1-029 -007 -986 -967 947 Mil -086 1-063 1-041 1-019 999 979 930 940 1-086 1-062 1-040 -017 997 977 957 I-I23 -098 1-075 1-052 1-030 I-OIO -990 940 950 1-098 1-074 1-051 028 1-007 987 -967 M35 no i -086 1-063 1-041 i -020 I -000 95 960 1-109 1-085 i -06 1 039 1-017 997 977 1-146 121 1-097 073 1-051 1-030 I-OIO 960 970 I-I20 1-096 1-072 -049 1-028 1-007 987 M58 133 1-108 084 1-062 1-041 i -020 970 980 I-I3I 1-107 1-083 060 1-038 1-018 997 I-I6 9 -144 1-119 095 1-073 1-052 1-031 980 990 I-I43 1-118 1-094 070 1-049 1-028 1-007 1-180 155 1-130 106 1-084 1-063 1-041 990 IOOO 1-129 1-105 -08 1 1-059 1-038 1-017 1-192 -167 1-142 -117 1-094 1-073 1-051 ooo HINTS TO METEOROLOGICAL OBSERVERS TABLE III. SPECIMEN OF THE TABLE TO BE PREPARED FOR REDUCING OBSERVA- TIONS OF THE BAROMETER TO SEA-LEVEL. ASSUMED ALTITUDE, 190 FEET. *l w rt .00 00000000 0000 vO t^OO ON O _ N ro^vo v^v^vSvo^R >-i CM ro Tf vo vo t^OO ON O i-i CM ro <* LOvO vovo vovo vO t^t^ t^l OO Ti- vovO t^OO vovo vovo vo ON O >" CM ro vovO vO vO vO rj- vovO t^OO ON O CM ro vO t^ t^* t^ t~. ^ vovO t^OO ON O i-i CM CO ^ > r^oo oo oo oo oo CM CO <* vovO I^OO ON O t-i CM co rh vovo t^OO ON O HH CM ro Tf vovO t^OO ON O w CM t>. t^ t^OO 00 00 O >-> CM ro Tf vo vovo vovo vovO t-^OO ON O t-i CM CO ^t- vD vO vO vO vO vovO t-00 ON O M CM ro TJ- vovO t^.00 ON O vovo vovo vo vO VO VO VO VO ^ ** >***'* c 00 ON O 1-1 CM rj- Tf vo vo vo CO ^- vovO t^ vo vo vo vo vo 00 ON O M CM vo vovO vO vO co ^ vovo r^ vO vO VO VO vO 00 ONO -i CM vo vO t> t^ t->. CO rf VOO t^OO CO vO t^.00 ON O i-i CM CO Tf vo VO 1^00 ON O t t CM CO ^ vo vo t^OO ONO i-i CM ro -^ voO g vO vo vO vO t^ .6 %f vovO f-00 ON O >-> N ro T^ vo vo vo vo rj- vovo r^oo vo vo vo vo vo ON O >- CM ro vovO VO vO VO VO vo vo \O O ON O CM ro * 1 "3.33: 3^. t^OO ON O M Tj- r}- rj- vo vo CM ro Tj- vovO vovo vovo vo t^OO ON O M vovo vovO vO CM ro --i rj- rf T^- vo VO N ro -^- vovo vo vo vo vo vo t^OO ON O CM vo vo vovO vO vO U O i- 1 CM ro rf vovO t^OO ON ro ro ro ro ro O >-< CM CO <* T^ T^ ^" ^" ^" vovO 1^00 ON ^ ^ ^ ^ rj- a fsj CO ^" vo vo vo vo vovO r^OO ON O vo vo vo vo vovO 00 ON O "-i CM CM CM CO CO CO ro * vovO t^ 00 ON O "H CM ro ro rf Tt- TJ- ro ^- vovo r^ OO ON O -< CM rl- Tj- vo vo vo CO ^J- vovO I^OO vovo vovo vovo w P4 D ^o t->oo o^ o CM CM CM CM CO 1-1 N ro ^ vo ro ro ro ro ro vO t^OO ON O CO CO CO CO I ^- >-> CM ro ^ vo VO t^OO ON O t-i CM CO ^j- vovO vo vo vo vo vo vo H K W rf vovO 1^00 CM CM CM CM CM ON O M N ro N ro ro ro ro r}- vovO 1^.00 ro ro ro ro ro ON O M CM ro ^t vovO t^OO ON O w CM CO Th rj- vo vo vo vo vo P* 1 CM CM CM CM CM I^OO ON O >-> N CM CS co ro CM CO *3" vovO ro co ro ro ro t^OO ON O M ro ro ro rt rj- ^-^5^ t^OO ON O *-> CM "3- * * vo vo vo H o >-> CM co <* V?^^rT O >-i CM ro ^d- ro ro ro ro ro vovO 1^.00 ON ro ro co co ro ^^^55 vovO t>00 ON O ^*- ^j- ^1- * ^t vo %?858 ro ^~ ^0*0 t^ 00 ON O >- CM CM CM ro ro ro co rt- vovO J^ co ro ro co co 00 ON O i-i CM roro 4 ^- ^*- ro Tj- vovO t-xOO vO 1-^00 ON O M N rorrvo vO t^OO ONO -i CM CO Tj- vo vO t^OO ON O w CM CO rj- vovO _, _, h-l HI CM CM CM CM N CM CM CM CM CM ro CO CO CO CO CO ro ro ro ro TJ- r}- * ^ rl- rf Tf ?^^ ON O M CM CO r}- vovO r^OO ON O *- CM co CM ro ro ro ro rh vovO t^OO ro ro ro ro ro ON Q M CM CO TJ- ro ^~ ^~ ^~ ^" ^ N CO ^ vovO t^OO ONO ~ CM ro Tf vovO t^OO ON O i-i CM ro rj- vovo t^OO ON O CM - CM co TJ- vovO t^OO ON O 1-1 N ro Tf vovO r^OO ON O >-> CM ro rj- vovO t^OO ON O fl O vO CM 00 TJ- 00 00 ON ON ON CM N CM CM CM O vO CM 00 < ^- CM CM rp rp Tf ON ON ON ON ON O vO CM 00 * vo vovO vO t^. c^^^^c^ O vO CM OO TJ- 00 00 ON ON O O vO CM 00 -vO vOtoto T*- T^- CO CO N to ON ^ ON CO cooo rot>. vo to to ^ O O O O N tv. hH vO O C O ON ONOO 00 N t^ HH VO M N W HH O O COOO N t^ HH vOHHioQto ONTJ-ON COOO COOO N t-% N t^ HH vO HH C O ON ONOO OO t^ t^vO vOto Tj-^-cOcON NhnwOO ON ONOO OO ON COOO N t>NvOHHvO QtoO ON ONOO 00 ^^ t^*vO vO to to ^ ^~ rf ON COOO co N hH hH O O HH VO HH VO O IO Tj- -^ co i ON T}- O O 9 9 ^ ON CO ONOO 00 CN! N HH O O ON ONOO 00 f^ t^v ^t*""" 99999 9 -00 fO vO vO IO 10 ^ TH- fO CO COOO M oo 1 00 coi^ N vO C O O ON ONOO SvO HH ON O 10 O to * ON ^OO C O O ON N t^ IH VO HH 00 t^ t^vO vO Hi? Nt^HHVOHH toOtoON-^- ON rhOO COOO co t^ OO t^ t^vO vO toiorj-coco NC4HHi-iO OON hH VO HHVO HH 10 10 to -3- ^t CO O to ON -^ ON co W 1-1 1-1 O t^ N t^ N VO t^ l^vO vO to 99999 hH vO O to ON ^" C HH O O ONOO 00 I-I N M CM hH hH hH c-o 10 O * ON TJ- 00 00 t^vO VO N t^ M VO HH CON N HH HH vO O to O O ON ON TJ- ON rJ-00 t^ t^>vO vO to 00000 COOO M t^ N CO N M HH HH to O to ON t^, t^VO >O .0090 O to O rt- ON Tf ON COOO CO OO N t>. N VOtOlOTt-CO CONMHHhH OOONOV OOcot^Nt^ HHVOHHIOO toO-^-ONTj- ON coOO co t^ OO 00 t-* 1>.VO VOlOlOrh 1 ^ COCONHHhH OOON ONOO O to ON Tf ON ONOO t~>i t^VO HH to O HH O O oo co r^ N vo HH v C hH hH O O ON ONC to o to O VO O to O Tf ON rhOO CO OOCOt^Nt^ NvOnnvOO toQtoO^ NOO oot->r^ vototo^-Tf COCONNHH HHOOONON oooot^ t-^vo hHhHhHHH hHhHhHhHhH hHhHNHhHhH hHhHhHQO OOOOO : : : : : : : . ON Tj-OO cor^ Mt^HHVOHH lOOtoON^J- ON rfOO COOO CO t~ M C hV hT O O ON ONOO OOJt>.t^ VOvOtO^-^- COCOMNhH ^ lOlOlOlOtO VO VO VO VO VO t^ oo oo oo oo oo 54 HINTS TO METEOROLOGICAL OBSERVERS TABLE VI. FOR CALCULATING THE DEW-POINT TEMPERATURE. Dry-bulb Thermometer. DIFFERENCE BETWEEN THE READINGS OF THE DRY-BULB AND WET-BULB THERMOMETERS. Dry-bulb Thermometer. I'O 2-0 3-0 4-0 50 6*0 70 80 90 id-o Amount to be subtracted from the Wet-bulb Reading to obtain the Dew-point. 10-0 7-8 15-6 23-3 3M 38-9 467 54-5 62-2 700 77-8 10-0 II-O 7-8 15-6 23-3 3i-i 38-9 467 54-5 62-2 7o-o i 77-8 II-O 12-0 7-8 15-6 23-3 3i-i 38-9 467 54-5 62 ' 2 70-0 77-8 I2-O 13-0 7-8 i5-S 23-3 3i-i 38-9 46-6 54-4 62-2 69-9 77-7 I 3 -0 14-0 7-8 15-5 23-3 31-0 38-8 46-6 54-3 62-1 69-8 77-6 I4-O 15-0 7-8 iS'5 23-3 31-0 38-8 46.5 54-3 62-0 69-8 77-5 15-0 16-0 77 i5'4 23-1 30-8 38-5 46-2 53-9 61-6 69-3 77-0 1 6-0 17-0 7-6 15-2 22-9 30-5 38-1 457 53-3 61-0 68-6 76-2 17-0 1 8-0 7-5 15-0 22-5 30-0 37-5 45' 52-5 60-0 67-5 75-o 18-0 19-0 7-3 147 22 -O 29-4 36-7 44.0 Si-4 587 66-1 73-4 19-0 20*0 7-i 14-3 21-4 28-6 357 42-8 50-0 57-i 64-3 71-4 20-0 20-5 7-0 14-0 21-0 28-0 35-i 42-1 49-1 56-1 63-1 70-1 20-5 21-0 6-9 13-8 2O-6 27-5 34-4 4i-3 48-2 55-o 61-9 68-8 21-0 21-5 6-7 13-5 20-2 27-0 337 40-4 47-2 53-9 607 67-4 21-5 22-0 6-6 13-2 I9-8 26-4 33-o 39-6 46-2 52-8 59-4 66-0 22-O 22-5 6-4 12-9 19-3 25-8 32-2 38-6 45-i 5i-5 58-0 64-4 22-5 23-0 6-3 12-6 18-8 25-1 3i-4 377 44-o 50-2 56-5 62-8 23-0 23-5 6-1 12-2 18-3 24-4 30-5 36-6 427 48-8 54-9 61-0 23-5 24-0 5-9 II-8 17-8 23-7 29-6 35-5 41-4 47-4 53-3 59-2 24-0 24-5 5-7 "5 17-2 22-9 287 34-4 401 45-8 51-6 57-3 24-5 25-0 5-5 IM 1 6-6 22-1 277 33-2 38-7 44-2 49-8 55-3 25-0 25-5 5-3 10-6 15-9 21-2 26-6 3i-9 37-2 42-5 47-8 53-i 25-5 26-0 5-i IO-2 J 5-2 20-3 25-4 30-5 35-6 40-6 457 50-8 26-0 26-5 4-9 97 14-6 19.4 24-3 29-1 34-o 38-8 437 48-5 26-5 27-0 4-6 9-2 13-8 18-4 23-1 277 32-3 36-9 4i-5 46-1 27-0 27-5 4-4 8-7 13-1 17-4 21-8 26-2 30-5 34-9 39-2 43-6 27-5 28-0 4'i 8-2 12-4 16.5 20- 6 247 28-8 33-o 37-i 41-2 28-0 28-5 3-9 7-7 1 1-6 15-5 19.4 23-2 27-1 31-0 34-8 387 28-5 29-0 3'6 7-3 10-9 14-5 18-2 21-8 25-4 29-0 327 36-3 29-0 29-5 3'4 6-8 10-2 13-6 17-0 20-3 237 27-1 30-5 33-9 29-5 30-0 3-2 6-3 9-5 12-6 15-8 18-9 22-1 25-2 28-4 3i-5 30-0 31-0 2-7 5-4 8-1 10-8 13-5 16-2 18-9 21-6 24-3 27-0 31-0 32-0 2-3 4-6 7-0 9-3 11-6 13-9 1 6-2 1 8-6 20-9 23-2 32-0 33-o 2-0 4-0 6-0 8-0 1 0-0 I2-I 14-1 16-1 18-1 20- 1 33-o 34-0 1-8 3-5 5-3 7-i 8-9 10-6 12-4 14-2 15-9 177 34-o 3S-o 1-6 3-2 4-8 6-4 8-0 9-6 1 1 -2 12-8 14-4 1 6-0 35-o 36-0 5 3-o 4-5 6-0 7-5 9-1 10-5 12-0 13-5 15-0 36-0 37-o 4 2-8 4-3 57 7-i 8-5 9-9 1 1-4 12-8 14-2 37-o 38-0 4 27 4-1 5'4 6-8 8-2 9-5 10-9 12-2 13-6 38-0 39-o 3 2-6 4-0 5-3 6-6 7-9 9-2 10-6 1 1-9 13-2 39-o 40-0 3 2-6 3-9 5-2 6-5 7-7 9-0 10-3 1 1-6 12-9 40-0 41-0 3 2-5 3'8 5-o 6-3 7-6 8-8 101 n-3 12-6 41-0 42-0 2 2-5 3-7 4-9 6-2 7-4 8-6 9-8 ii-i 12-3 42-0 43-o 2 2-4 3-6 4-8 6-0 7-2 8-4 9-6 10-8 I2-O 43-o 44.0 2 2-4 3-5 47 5'9 7-i 8-3 9.4 10-6 n-8 44-0 45-o 2 2-3 3-5 4-6 5-8 7-o 8-1 9-3 10-4 11-6 45-o 46-0 2-3 3-4 4-6 57 6-8 8-0 9-1 103 11.4 46-0 47-o 2-2 3-4 4-5 5-6 6-7 7-8 Q'O IO-I II-2 47-0 48-0 2-2 3-3 4.4 5-5 6-6 7-7 8-8 9-9 II-O 48-0 49-0 2-2 3-2 4-3 5-4 6-5 7-6 8-6 97 10-8 49-o 50-0 2-1 3'2 4'2 5-3 6-4 7-4 8-5 9-5 10-6 50-0 DEW POINT 55 TABLE VI. FOR CALCULATING THE DEW-POINT TEMPERATURE. Continued. Dry-bulb Thermometer. DIFFERENCE BETWEEN THE READINGS OF THE DRY-BULB AND WET-BULB THERMOMETERS. Dry-bulb Thermometer. i f o 2 f O 3 f O 4-0 5-0 60 7 f O 80 90 iQ-o|iro 12-0 13-0 14'0 15-0 Amount to be subtracted from the Wet-bulb Reading to obtain the Dew-point. 50 II 2-1 3-2 4-2 53 6-4 50 7-4 8-5 9-5 xo-6 11-7 12-7 13-8 14-8 15-9 51 I-O 2-1 3-i 4-2 5'2 6-2 7-3 8-3 9-4 10-4 1 1-4 I2 -5 i3-5 14-6 15-6 51 5 2 I-O 2-0 3'i 4-1 5-i 6-1 7-1 8-2 9-2 IO-2 II-2 12-2 i3-3 14-3 15-3 52 53 I-O 2-O 3-o 4-0 5-o 6-0 7-o 8-0 9-0 1 0-0 I I-O 12-0 13-0 14-0 15-0 53 54 I-O 2-0 2-9 3'9 4-9 5-9 6-9 7-8 8-8 9-8 10-8 1 1-8 12-7 i37 14-7 54 55 I-O 1-9 2-9 3-8 4-8 5-8 6-7 7-7 8-6 9-6 10-6 n-5 12-5 i3-4 14.4 55 56 0-9 i -9 2-8 3-8 47 5-6; 6-6 7-5 8-5 9-4 10-3 n-3 12-2 13-2 14-1 56 57 0-9 1-8 2-8 37 4-6 5'5 6 '4 7-4 8-3 9-2 IO-I I I-O 12-0 12-9 13-8 57 58 0-9 1-8 2-7 3-6 4-5 5'4 6-3 7-2 8-1 9-0 9-9 10-8 11-7 12-6 13-5 58 59 0-9 1-8 2-7 3-6 4-5 5-3 6-2 7-i 8-0 8-9 9-8 10-7 11-6 12-5 13-4 59 60 0-9 i-8 2-6 3-5 4.4 5-3 6-2 7-0 7-9 8-8 9-7 10-6 1 1-4 12-3 13-2 60 61 0-9 i-7 2-6 3-5 4.4 5-2 6-1 7-0 7-8 8-7 9-6 10-4 n-3 12-2 i3-i 61 62 0-9 i-7 2-6 3'4 4-3 5'2 6-0 6-9 7-7 8-6 9-5 10-3 II-2 I2-O 12-9 62 63 0-9 i-7 2-6 3'4 4-3 5' 1 6-0 6-8 77 8-5 9-4 10-2 II-I 11-9 12-8 63 64 0-8 i-7 2-5 3-3 4'2 5-o 5'8 6-6 7-5 8-3 9-1 1 0-0 10-8 1 1-6 12-5 64 65 0-8 1-6 2-5 3-3 4'i 4-9 57 6-6 7-4 8-2 9-0 9-8 10-7 "5 12-3 65 66 0-8 1-6 2-4 3'2 4-1 4.9 5-7 6-5 7-3 8-1 8-9 97 10-5 n-3 12-2 66 67 0-8 i-6 2-4 3'2 4-0 4-8 5-6 6-4 7-2 8-0 8-8 9.6 10-4 II-2 12-0 67 68 0-8 1-6 2-4 3-2 4-0 47 5-5 6-3 7-i 7-9 8-7 9-5 10-3 II-I 1 1-9 68 69 0-8 1-6 2-3 3'i 3'9 4-7 5-5 6-2 7-0 7-8 8-6 9.4 IO-I 10-9 11-7 69 70 0-8 J -5 2-3 3-i 3-9 4-6 5-4 6-2 6-9 7-7 8-5 9-2 10-0 10-8 11-6 70 71 0-8 *-5 2-3 3-o 3-8 4-6 5-3 6-i 6-8 7-6 8-4 9-1 9-9 10-6 1 1-4 71 72 0-8 i-5 2-3 3-o 3-8 4-5 5-3 6-0 6-8 7-5 8-3 9-0 9-8 10-5 n-3 72 73 0-7 !'5 2'2 3-o 3-7 4-4 5-2 5-9 6-7 7-4 8-1 8-9 9-6 10-4 ii-i 73 74 o-7 i-5 2*2 2-9 37 4.4 5-i 5-8 6-6 7-3 8-0 8-8 9-5 IO-2 I I-O 74 75 o-7 1-4 2-2 2-9 3-6 4'3 5-o 5-8 6-5 7-2 7-9 8-6 9-4 IO-I 10-8 75 76 0-7 1-4 2-1 2-8 3-6 4-3 5- 57 6-4 7-i 7-8 8-5 9-2 9'9 10-7 76 77 0-7 1-4 2-1 2-8 3-5 4-2 4-9 5-6 6-3 7-o 7-7 8-4 9-1 9*8 10-5 77 78 o-7 1-4 2-1 2-8 3-5 4-1 4-8 5-5 6-2 6-9 7-6 8-3 9-0 97 10-4 78 79 o-7 1-4 2-1 2-8 3-5 4-1 4-8 5-5 6-2 6-9 7-6 8-3 9-0 97 10-4 79 80 0-7 1-4 2-0 27 3-4 4-1 4-8 5-4 6-1 6-8 7-5 8-2 8-8 9-5 10-2 80 81 07 1-4 2-0 2-7 3-4 4-1 4-8 5-4 6-1 6-8 7-5 8-2 8-8 9-5 IO-2 81 82 0-7 1-3 2-0 2-7 3-4 4-0 4-7 5-4 6-0 6-7 7-4 8-0 8-7 9-4 10- 1 82 83 o-7 i-3 2-0 2-7 3'4 4-0 47 5'4 6-0 6-7 7-4 8-0 8-7 9-4 IO-I 83 84 o-7 1-3 2-0 2-6 3-3 4-0 4-6 5-3 5-9 6-6 7-3 7-9 8-6 9-2 9-9 84 85 o-7 i-3 2-0 2-6 3-3 3-9 4-6 5-2 5-9 6-5 7-2 7-8 8-5 9-1 9-8 85 86 0-7 i-3 2-0 2-6 3-3 3-9 4-6 S- 2 5-9 6-5 7-2 7-8 8-5 9-1 9-8 86 87 0-6 i-3 1-9 2-6 3-2 3-8 4-5 5-i 5-8 6-4 7-0 77 8-3 9-0 9-6 87 88 0-6 '3 1-9 2-6 3-2 3-8 4-5 5' 1 5-8 6-4 7-0 77 8-3 9-0 9-6 88 89 0-6 i-3 1-9 2-5 3-2 3-8 4-4 5-o 57 6-3 6-9 7-6 8-2 8*8 9-5 89 90 0-6 i-3 i-9 2-5 3-2 3-8 4-4 5-o 57 6-3 6-9 7-6 8-2 8-8 9-5 90 91 0-6 1-2 i-9 2 '5 3'i 37 4'3 5-o 5-6 6-2 6-8 7-4 8-1 8-7 9-3 91 92 0-6 1-2 1-9 2-5 3'i 37 4-3 5-o 5-6 6-2 6-8 7-4 8-1 8-7 9-3 92 93 0-6 1-2 1-8 2-4 3-i 37 4-3 4-9 5-5 6-1 6-7 7-3 7*9 8-5 9-2 93 94 0-6 1-2 1-8 2-4 3-o 3-6 4-2 4-8 5-4 6-0 6-6 7-2 7-8 8-4 9-0 94 95 0-6 1-2 1-8 2-4 3-o 3-6 4-2 4-8 5-4 6-0 6-6 7-2 7-8 8-4 9-0 95 96 0-6 1-2 1-8 2-4 3- 3-5 4-1 47 5-3 5-9 6-5 7-i 77 8-3 8-9 96 97 0-6 1-2 i-8 2-4 3-o 3-5 4-1 4-7 5-3 5-9 6-5 7-i 77 8-3 8-9 97 98 0-6 1-2 1-8 2-3 2-9 3-5 4-1 4-6 S- 2 5-8 6-4 7-0 7-5 8-1 8-7 98 99 0-6 1-2 1-8 2 '3 2-9 3-5 4-1 4-6 5'2 5-8 6-4 7-0 7-5 8-1 8-7 99 100 0-6 I-I i-7 2'3 2-9 3-4 4-0 4-6 5-i 5-7 6-3 6-8 7-4 8-0 8-6 100 HINTS TO METEOROLOGICAL OBSERVERS TABLE VII. ELASTIC FORCE OF AQUEOUS VAPOUR IN INCHES OF MERCURY. 2 S 6 3 H o-o 01 0-2 0-3 0'4 0'5 0-6 0-7 0'8 0'9 &J I 2 In. In. In. In. In. In. In. In. In. In. 0-044 0-044 0-044 0-045 0-045 0-045 0-045 0-045 0-046 0-046 I 046 046 046 047 047 047 047 047 048 -048 I 2 048 048 048 049 049 049 049 049 050 050 2 3 050 050 050 051 051 051 051 051 052 052 3 4 052 052 052 053 053 053 053 053 054 054 4 5 054 054 055 055 055 055 056 056 056 056 5 6 057 057 057 058 058 058 059 059 059 059 6 7 -060 060 -060 -060 060 06 1 -06 1 06 1 06 1 062 7 8 -062 062 062 063 063 063 063 064 064 064 8 9 065 -065 -065 066 066 066 -066 067 067 067 9 10 -068 068 068 069 069 069 -069 070 070 070 10 n 071 071 071 072 072 072 -072 073 073 073 II 12 074 074 075 075 075 076 076 077 077 077 12 I 3 078 078 078 079 079 080 -080 08 1 -08 1 081 13 14 082 082 082 083 083 084 084 085 085 085 14 15 086 086 086 087 087 088 088 089 089 089 15 090 090 090 091 091 092 092 093 093 093 16 17 094 094 094 095 095 096 096 097 097 097 17 18 098 098 099 099 IOO IOO 101 101 102 IO2 18 19 103 103 104 104 105 105 106 106 107 107 19 20 -108 108 109 109 no no in in 112 112 20 21 113 113 114 114 US "5 116 116 117 117 21 22 118 118 119 119 I2O I2O 121 121 122 122 22 23 123 124 124 125 125 126 127 127 128 128 23 2 4 129 130 130 'W 131 I 3 2 133 133 134 134 " 24 25 135 136 136 137 137 138 139 139 I4O I4O 25 26 141 142 142 H3 143 144 145 145 I 4 6 146 26 27 147 148 148 149 149 150 I5 1 *5* 152 IS 2 27 28 153 154 154 155 I 5 6 156 i57 158 I 5 8 159 28 29 160 160 161 162 162 164 165 -166 166 29 30 167 168 168 169 .170 .170 171 172 172 173 30 3 1 174 174 175 176 I 7 6 177 178 179 179 180 31 32 181 182 182 183 I8 4 184 185 186 186 187 32 33 188 188 189 190 191 192 i93 193 194 195 33 34 196 196 197 198 199 199 200 201 202 -203 34 35 204 204 205 206 207 208 208 209 210 211 35 36 212 213 214 214 215 216 217 218 218 219 36 37 22O 221 222 223 224 225 225 226 227 228 37 38 229 2 3 2 3 I 231 232 233 234 235 236 237 38 39 238 2 3 8 239 240 241 242 243 244 245 246 39 40 247 248 249 250 251 252 253 254 255 -2 5 6 40 41 258 259 -260 26l 262 263 264 265 266 41 42 267 -268 .26 9 270 .271 272 273 274 276 42 43 277 2 7 8 279 -280 28l 283 284 286 -287 43 44 288 289 290 292 293 294 295 296 297 298 44 45 299 301 -302 303 304 305 306 307 308 39 45 46 312 313 315 316 317 318 319 321 322 46 47 323 324 325 327 328 329 330 331 333 334 47 48 335 336 338 339 340 342 343 344 345 346 48 49 348 349 351 352 353 355 356 357 358 360 49 50 0-361 0-362 0-364 0-366 0-367 0-369 0-370 o-37i o-373 50 ELASTIC FORCE OF AQUEOUS VAPOUR 57 TABLE VII. ELASTIC FORCE OF AQUEOUS VAPOUR IN INCHES OF MERCURY. Continued. rt II ~ o-o 01 (ft 03 0-4 05 0-6 07 0-8 09 III E 3 H" In. In. In. In. In. In. In. In. In. In. 60 0-361 0-362 0-364 0-365 0-366 0-367 0-369 0-370 0-371 o-373 50 51 374 375 377 378 379 381 382 384 385 386 51 52 388 389 391 393 394 396 397 399 400 401 52 53 403 -404 406 -407 -409 410 412 413 415 416 53 54 418 419 421 .422 424 425 427 428 43 431 54 55 433 434 436 437 439 -441 443 444 446 447 55 56 449 451 453 454 456 457 459 461 462 -464 56 57 465 467 .469 470 -472 473 475 477 479 480 57 58 482 483 485 487 489 491 492 494 496 498 58 59 500 .501 503 505 507 509 5" 512 514 -516 59 60 .518 520 522 524 .526 -528 529 531 533 535 60 61 537 539 541 543 545 546 548 550 552 554 61 62 556 558 .560 .562 564 .566 568 570 572 574 62 63 576 578 .580 -582 584 -586 588 590 592 594 63 64 .596 598 601 603 -605 -607 609 611 613 -615 64 65 617 620 -622 624 -626 628 630 633 635 637 65 66 639 641 644 646 648 650 652 655 657 659 66 67 661 664 666 668 -671 673 675 678 680 682 67 68 684 687 -689 692 -694 697 699 701 704 -706 68 69 .708 711 713 .716 -718 -721 723 726 728 731 69 70 733 736 738 741 744 746 749 751 754 756 70 71 759 761 764 766 769 772 774 777 779 -782 71 72 785 788 790 793 796 799 80 1 804 -807 810 72 73 812 815 -818 820 823 -826 829 832 834 837 73 74 840 843 -846 -848 -851 854 857 860 863 .865 74 75 868 871 874 877 -880 883 885 888 -891 894 75 76 897 900 903 -906 -909 912 915 918 921 924 76 77 927 930 934 937 -940 943 946 949 952 955 77 78 958 -961 965 0-968 0-971 0-974 0-977 0-981 0-984 0-987 78 79 0-990 0-994 0-997 I-OOO 1-003 1-007 I-OIO 1-013 1-016 1-020 79 80 81 -023 057 1-026 i -060 1-030 1-064 1-033 1-067 1-037 1-070 040 074 1-043 1-077 1-047 i -08 1 1-050 1-084 1-053 1-088 80 81 82 -092 1-095 1-099 1-103 106 no 1-114 1-117 I-I2I I-I24 82 83 128 1-131 I-I35 i-i39 -142 146 1-150 I-I54 I-I57 1-161 83 84 165 1-169 I-I73 1-176 180 184 1-188 1-192 I-I96 1-200 84 85 203 1-207 1-211 1-215 -219 222 1-226 1-230 1-234 1-238 85 86 -242 1-246 I-25O 1-254 -258 262 1-266 1-270 1-274 I-278 86 87 282 1-286 I-290 1-295 299 303 1-307 1-311 I-3I5 i-3 J 9 87 88 323 1-328 1-332 I-336 340 345 1-349 1-353 1-357 1-361 88 89 366 1-370 1-375 1-379 384 388 1-393 1-397 1-401 1-406 89 90 410 I-4I5 1-419 1-424 -428 433 1-437 1-442 1-446 i-45i 90 91 455 1-460 1-464 1-469 473 478 1-483 1-487 1-492 1-496 91 92 501 I-505 1-510 i-5i5 5i9 524 1-529 1-534 I-538 1-543 92 93 548 i-553 i-557 1-562 -567 572 1-577 1-581 1-586 i-59i 93 94 -596 1-601 1-606 1-611 616 621 1-626 1-631 1-636 1-641 94 95 646 1-651 1-657 1-662 .667 672 1-677 1-682 1-687 1-692 95 96 697 751 1-703 1-757 1-708 1-762 1-714 1-768 719 773 724 779 1-730 1-784 1-735 1-790 1-741 1-795 1-746 1-801 96 97 98 806 1-811 1-817 1-822 -828 833 1-839 1-845 1-850 1-856 98 99 862 1-868 1-873 1-879 884 890 1-896 1-901 1-907 1-912 99 100 918 1-923 1-929 !-935 941 947 1-953 1-959 1-965 1-971 100 HINTS TO METEOROLOGICAL OBSERVERS 00 co SN XO -vO 00 vO vO N CO Tj- lovO VO t^OO 00 ON ON O N vOvOvOvOvS vOvOvOvOvO VOt^t> 00 i-< N vo ONVO lOvO vO vO vO CO TJ- vovO t^ t^OO 00 ON ON VOvOvOvOvO \O vO vO vO vo O O N TJ- 10 00 N COvO vO vO vO vO vO vO vO vO vO vO vO ' W HH fO Tj- 10 10 #$S8# v^RR^r. .KrR C\ TJ- vooo co O w w 1-1 CM co t^t^ moo 1-1 vO r^OO ONO O <-< ** tt t* coco vovO O vo t-* ON vo 00 ON ON O i-i i-i N N co co 9 I-H vO 00 i-i vO co OOvOOco Tt-vot^t^OO *^t hH KH HH CNl N CO TJ->O VOVO VO VO VO VO VO VO TJ- vo vovO vo OwMp^CO COTj-rfLO' 1 I-H N) CNl fO TJ- TJ-VOVOVOVO vo f^OO ON O O fl 1-1 OO >-i >-> N N ro CO CO CO Tj- vo vovO vO r^. ^ OO HH vo ON CO O 4jl M N N N COTJ- vO vO vO ONOO COOO O w N co co TJ- t^oo oo oo oo co I-H O ""> ON t-i lOvO vO vO t^. i-i Tf ONVO CO I-H t^ i-i CO rj- 10VO vO t^ t^OO OO ON 00 00 00 00 00 vO t^OOOO ON t^ t^r^ t^t^ CO CO CO TJ- Tj- VO tl^vo S 03 ON T^ tx.OO ON O HH i^ i^ vovor^t^r^ t^oo oo oo oo 00 M TJ- t^ i-i CO Tj- T}- Tj- LO NVO vO VO t^.00 00 00 i 0000 00 0000 00 00 ON ON ON O O O 00 00 00 ON ON ON n 00 "i CO t-x H-I vO r-4 TJ- vo vo vovO vO oo oo oo oo 00 OO 00 OO O O i-< w O O O O i-i <-> i-i ON ON ON ON ON ON s N O ^O 00 00 00 00^ '06* ONONONONON ONONONO N COvo ON N vO > ON vO Tj~ r^ ON ON O O O *" hH 00 OO 00 CO ON ON ON ON ON G > i ON ON ON ON ON ON ON ON ON ON ON ON O^ OS ON ON ON ON ON ON vovO vO vO ON ON ON ON ON ON ON ON ON ON vO vQ vD vO vO ON ON ON ON ON vO vO OO 00 OO 00 O^ O^ O* 1 * O 1 * O^ 888888 88888 88888 88888 88888 88888 O O rH 00 M O N rJ-vO 00 RELATIVE HUMIDITY 59 #> S3-T IO vo vo vo to -00 ON O ; ; IOVO HI 1^00 O HI CO totovO vO vO t^ ON O N ^t tOtovO vO vO s HI H4 N CO CO to to to to S : : vovo oo co tovO vO vO vO 00 vovO ON Tt HI ONVO O CO HI C/J f^ CO ^ *3- 10 t^OO ON O to to to to to 00 ON O HI - TJ- rt tou-> vO vO vO vO vO i vot^ O vo CO O 1 M HI N CO ' to to to to to vO vO vO vO vO ON ON ON O HI ON O to\o ; tovO 00 HI >O to to to to ts,00 ON O O HI N N CO vovO 00 to vo vovO vO vO vO vO vO vO vO vO ; to l^ ON N t* to 'O to to to vO *> ON COOO t^OO 00 ON O HI to vo vo vovO vO vO vO vO vO vO N rj- vovO t^ OO ON ON O HI to to vo vo to to vo vovO vO tovO t^ ON O vO vO vO vO t^ vooo o o Tf o O HI t^r>. t^ ON 1-1 vo HI ON t^ 10 ON N vO vO cb rj- tovO \O VO vO VO vO N HI ON COVO vo r^OO 00 ON ON O vO vO vO vO vO vO X s ** eo co co co co o N -^-vo oo O vO vO vO vO t- r^oo a* 6o HINTS TO METEOROLOGICAL OBSERVERS SuipBa^j qtnq-jfca N "tf-vO 00 ON "tf-vO 00 iH C* N IN c* N co roro ro co O N rd-\O OO ^ TJ-rtTf* SN --d-vO OO vovo vr>vo O H DIFFERENCE BETWEEN THF, READINGS OF THE DRY-BULB AND WET-BULB THERMOMETERS. s t^OO ON O O HH HH W M N N N N M N t^OO ON O -" N N N ro ro i-i CO VOOO M co co ro CO Tt g i-H t^OO ON O O HH M l-l N N HH ro rj- vot^ M N N N N 00 ON ON O >-" N N N coro N Tt VOOO i-i co co ro ro ^t :::::: :* 2 J?J? 5 ...... t^ _, Tt-VO 2*8 3 3 N ^ vovO OO N N N N N 00 ON ON -( N IN ts C4 ro ro N rt- vo ON N co ro ro ro T}- * t*- i i :::::: : *^ M ^^ 00 ON O <->>-> W HH M N N N rj- vo\O OO N N N N N N ro ro ro ro co vovO ON M COCO CO CO Tj- ;: ts, M Ttf-vO 00 ON O " N ro * vot>00 N N M N N ON O O N ro N ro ro ro ro ro vovO O CO coco CO <* Tt c fc ...... ; t^ N vor> ON O >-" "-H N M N N N N rj- vo\O t^ ON N N N N N O HH M N ro ro ro ro ro ro rf vo t^ O CO co ro ro -?t Tj- 00 s ON O "i N N N N N N JTff^S O w M N ro TfvO t^ O co ro ro ro Tf ^f CO 'S :::::: : oo N vo oo O *-" N ro ro N N N N N vovO t^OO O N M N N ro w N M ro rh ro ro ro roro vovO 00 w <^ CO CO CO Tf Tj- TH s ...... -oo rovO 00 O H N fO fO N N N N N vovO t^ ON O N N M N ro w N N ro ^d- ro ro ro ro ro vot^OO w rf CO CO CO Tl- rf c^ s -i N fO * rj- N N N N N ^O r^OO ON w N N N N ro N ro ro rf vo co ro ro ro ro vo r-^ ON N vo CO CO CO Tj- * "1 rj- ON ro t^ ON M N fO Tj- vo N M M N N v5 t^OO O 1-1 N N N ro ro M ro rj- rh vo ro co co co co vO 00 ON N vo ro ro ro rf ^f 00 s :::::: * ON ^oo o N ro -H covo CO CO Tj- Tj- rf ^ o 1 1 ro TJ- vovO t^ N N N N N 00 ON O M ro N N rororo Tf vovO vO l^ ro ro co co co 00 O >- T(- t^ ro * Tt rj- TJ- :::::: ^2 If 3 p IO i vo O vo O "-> ro ^- vr>>o 00 N N N M N ON O n ro rf N ro ro ro ro vo vovO t^-00 co co ro ro ro 00 O tN ^-t^ CO T;)- Tt Tf rj- :::::: IN M oo s vo i- vo O N :::::: N IN rj- voO t^ ON N N N N M O M N ro rh roro ro ro ro vovO t^OO 00 ON w CO VOOO ro Tj- rh TJ- TJ-

M ro -.00 00 CO CO CO CO CO ON M ro vooo ,_! HH N C4 "* s vO w vO >-" CO :::::: w N c* vovO t^OO ON N N N N N -< M ro ^ vo ro ro ro ro ro vO t^OO ON ON O vN rhvo 00 <* rf n- TJ- T^- 0^ ^J vo N t^ IN co vovO 00 ON O N N N N ro M N ro rt- vo ro ro ro ro ro vO t^.00 ON ON ro co co ro ro O M -. moo co <* \O t** ON O <-" N N N ro ro N rj- vo vot^ ro ro ro ro ro 1^00 ON O O rococo^ ^3- >-l Tj- VOOO O <* Tt- ?!- Tf vo 5 t^ cooo co vo : : '. '. . . -> 1-1 N IN r^oo O w N N N ro ro ro ro vovO >O 00 ro ro ro ro ro 00 ON O >-i w co ro * Tl- rt IN TfvO 00 O H w ro ro rt Tf rj- M vovO ON >-< ** ^ ^J- <* vo r^ >H N N N ON O N ro rj- N ro ro ro ro vor^oo ON O ro ro ro ro ^* l-l N CO Tt- Tj- rj- rf TJ- Tj- TJ- VOt^OO HH CO Tf Tj- Tt- VO VO s ; : ;" ^^^^^ O i-i ro rj- vr> rororororo vO 00 ON O "-I ro ro ro ^ ^i- N ro ^- vo vo Tj- Tf Tt Tj- Tj- VO 00 ON N TJ- ^- ^- rj- vo vo o ^O rot^ O : : : . : -< M N N ^ 1-1 H- ro rf vo ro ro ro ro ro t^OO ON O N ro ro ro rf Tf N ro rt- vo vo rj- r}- ^ Tj- TT vO 00 ON N T}- ^- Tj- rt vo vo O g 10 O vo ro r^. ON " w w M N ri <-> N TJ- vo\O ro ro ro ro ro 00 ON O M ro ro ro Tf Tf Tt CO rt- vovO vO ^ Tj- Tf rj- rj- 1^ ON O CO vo T^- Tj- vo vo vo 3uipl23}{ qjnq-AJQ *O O N Tl-vO 00 ON -^-vO 00 tH N N N N N COfOrOroro O N -^-vO OO N TtvOOO VO VO VO VO O vO vO vO vO O VOO O O t- t^OO OS O H ENGLISH AND METRICAL BAROMETER SCALES 61 TABLE IX. COMPARISON OF THE ENGLISH AND METRICAL BAROMETER SCALES. ( I inch = 25-39954 millimetres. ) English inches. Milli- metres. English inches. Milli- metres. English inches. Milli- metres. English inches. Milli- metres. 27-OO 685-8 28-OO 7II-2 29-00 736-6 30-00 762-D 27-02 686-3 28-02 7II-7 29-02 737-1 30-02 762-5 27-04 686-8 28-04 712-2 29-04 737-6 30-04 763-0 27-06 687.3 28-06 712-7 29-06 738-I 30-06 763-5 27-08 687-8 28-08 7I3-2 29-08 738-6 30-08 764-0 27-IO 688.3 28-10 7I3-7 29-IO 739-1 30-10 764-5 27-12 688-8 28-12 714-2 29-12 739-6 30-12 765-0 27-14 689-3 28-14 714-7 29-14 740-1 30-14 765-5 27-16 689-9 28-16 7I5-3 29-16 740-7 30-16 766-1 27-18 690-4 28-18 715-8 29-18 741-2 30-I8 766-6 27-20 690-9 28-2O 7I6-3 29-20 741-7 30-20 767-1 27-22 691.4 28-22 716-8 29-22 742-2 30-22 767-6 27-24 691-9 28-24 7I7-3 29-24 742-7 30-24 768-1 27-26 692-4 28-26 717-8 29-26 743-2 30-26 768-6 27-28 692-9 28-28 718-3 29-28 743-7 30-28 769-1 27-30 693-4 28-30 7I8-8 29-30 744-2 30-30 769-6 27-32 693-9 28-32 7I9-3 29-32 744-7 30-32 770-1 27-34 694-4 28-34 719-8 29-34 745-2 30-34 770-6 27-36 694.9 28-36 720-3 29-36 745-7 30-36 77I-I 27-38 695-4 28-38 720-8 29.38 746-2 30-38 771-6 27-40 696-0 28-40 721-4 29-40 746-8 30-40 772-2 27.42 696-5 28-42 721-9 29.42 747-3 30-42 772-7 27-44 697-0 28-44 722-4 29-44 747-8 30-44 773-2 27-46 697-5 28-46 722-9 29-46 748-3 30-46 773-7 27-48 698-0 28-48 723-4 29-48 748-8 30-48 774-2 27-50 698-5 28-50 723-9 29-50 749-3 30-50 774-7 27-52 699-0 28-52 724-4 29.52 749-8 30-52 775-2 27-54 699-5 28.54 724-9 29-54 750-3 30-54 775-7 27-56 700-0 28-56 725-4 29-56 750-8 30-56 776-2 27-58 700-5 28-58 725-9 29.58 751-3 30-58 776-7 27-60 701-0 28-60 726-4 29-60 751-8 30-60 777-2 27-62 7oi-5 28-62 726-9 29-62 752-3 30-62 7777 27-64 702-0 28-64 727-4 29-64 752-8 30-64 778-2 27-66 702-6 28-66 728-0 29-66 753-4 30-66 778-8 27-68 703-1 28-68 728.5 29-68 753-9 30-68 779-3 2770 703-6 28-70 729-0 29-70 754-4 30-70 779-8 2772 704-1 28-72 729-5 2972 754-9 30-72 780-3 27-74 704-6 28-74 730-0 2974 755-4 30-74 780-8 2776 705-1 28-76 730-5 29.76 755-9 30-76 78i-3 27-78 705-6 28-78 731-0 2978 756-4 30-78 781-8 27-80 706-1 28-80 731-5 29-80 756-9 30-80 782-3 27-82 706-6 28-82 732-0 29-82 757-4 30-82 782-8 27-84 707-1 28-84 732-5 29-84 757-9 30-84 783-3 27-86 707-6 28-86 733-o 29-86 758-4 30-86 783-8 27-88 708-1 28-88 733-5 29-88 758-9 30-88 784-3 27-90 708-7 28-90 734-1 29-90 759-5 30-90 784-9 27-92 709-2 28-92 734-6 29-92 760-0 30-92 785-4 27-94 709-7 28-94 735' 1 29-94 760-5 30-94 785-9 27-96 710-2 28-96 735-6 29-96 761-0 30-96 786-4 27-98 710-7 28-98 736-1 29-98 76i-5 30-98 786-9 62 HINTS TO METEOROLOGICAL OBSERVERS TABLE X. COMPARISON OF THE FAHRENHEIT AND CENTIGRADE THERMOMETER SCALES. (i Fahrenheit = o.$$6 Centigrade.) Fahr. Cent. Fahr. Cent. Fahr. Cent. Fahr. Cent. Fahr. Cent. -20-0 -28-9 + 100 - 12-2 + 40-0 + 4-4 + 70-0 + 2I-I + 100-0 + 37-8 -19-5 -28-6 io-5 -11-9 40-5 4-7 70-5 21-4 100-5 38-1 -19.0 -28-3 I I-O -11-7 41-0 5* 71-0 217 IOI-0 38-3 -18-5 -28-1 II *5 -i 1-4 41-5 5-3 71-5 21-9 101-5 38-6 - 1 8-0 -27-8 12-0 n-i 4 2-0 5-6 72-0 22-2 IO2-O 38-9 -17-5 -27-5 12-5 -10-8 42-5 5-8 72-5 22-5 IO2-5 39-2 -17-0 -27-2 13-0 - 10-6 6-1 22-8 I03-0 39-4 -16-5 -26-9 -10-3 43-5 6-4 73-5 23-1 103-5 39-7 - 1 6-0 -26-7 14-0 -10-0 44-o 6-7 74-o 23-3 IO4-O 40-0 -15-5 -26-4 14-5 - 9-7 44-5 6-9 74-5 23-6 104-5 40-3 -15-0 -26-1 15-0 - 9-4 45- 7-2 75-o 23-9 IO5-O 40-6 -14-5 - 14-0 -25-8 -25-6 '5'5 1 6-0 - 9-2 - 8-9 45-5 46-0 7-8 75-5 76-0 24-2 24-4 105-5 I O6-O 40-8 41-1 -13-5 -25-3 16-5 - 8-6 46-5 8-1 76-5 24-7 I06-5 41-4 -13-0 -25-0 17-0 - 8-3 47-0 8-3 77-o 25-0 IO7-O 41-7 -12-5 -24-7 17-5 - 8-1 47-5 8-6 77-5 25-3 107-5 41-9 - 12-0 -24-4 18-0 - 7-8 48-0 8-9 78-0 25-6 1 08-0 42-2 - n-5 -24-2 18-5 - 7-5 48-5 78-5 25-8 108-5 42-5 - I I-O -23-9 19-0 - 7-2 49-o 9-4 79-o 26-1 109-0 42-8 -10-5 -23-6 19-5 - 6-9 49-5 9-7 79-5 26-4 109-5 -10-0 -23-3 20-0 - 6-7 50-0 10-0 80-0 26-7 110-0 43-3 - 9-5 -23-1 20-5 - 6-4 50-5 10-3 80-5 26-9 110-5 43-6 - 9-0 -22-8 21-0 - 6-1 51-0 10-6 81-0 27-2 1 1 I-O 43-9 - 8-5 -22-5 21-5 - 5-8 51-5 10-8 81-5 27-5 111-5 44-2 - 8-0 -22-2 22-0 - 5-6 52-0 IM 82-0 II2-O 44-4 - 7-5 -21-9 22-5 - 5-3 52-5 1 1-4 82-5 28-1 II2-5 44-7 - 7-0 -21-7 23-0 - 5-0 53-0 11-7 83-0 28-3 II3-O 45-o - 6-5 -21-4 23-5 - 4-7 53-5 11-9 83-5 28-6 "3-5 45-3 - 6-0 -2I-I 24-0 - 4-4 54-o 12-2 84-0 28-9 114-0 45- 6 - 5-5 -20-8 24-5 - 4-2 54-5 12-5 84-5 29-2 1 14-5 45-8 - 5-0 -2O-6 25-0 - 3-9 55-o 12-8 85-0 29-4 115-0 46-1 - 4-5 - 4-0 -20-3 -20-0 26-0 - 3-6 - 3-3 55-5 56-0 13-1 13-3 85-5 86-0 29-7 30-0 ii5-5 1 1 6-0 46-4 46-7 - 3-5 -19-7 26-5 - 3-1 56-5 13-6 86-5 30-3 116-5 46-9 -19.4 27-0 - 2-8 57-o 13-9 87-0 30-6 117-0 47-2 - 2-5 - 19-2 27-5 - 2-5 57-5 14-2 87-5 30-8 II7-5 47-5 - 2-O -18-9 28-0 - 2-2 58-0 14-4 88-0 3*" 1 1 1 8-0 47-8 - 1-5 -18-6 28-5 - 1-9 58-5 14-7 88-5 3i-4 118-5 48-1 - I-O -18-3 29-0 - 1-7 15-0 89-0 119-0 48-3 - 0-5 -18-1 29-5 - 1-4 59-5 15-3 89-5 3 I- 9 I1 9'5 48-6 0-0 -17-8 30-0 - i-i 60-0 15-6 90-0 32-2 120-0 48-9 + 0-5 -17-5 30-5 - 0-8 60-5 15-8 90-5 32-5 120-5 49-2 I-O -17-2 3 I-0 - 0-6 61-0 16-1 91-0 32-8 I2I-0 49-4 1-5 - 16-9 3 X 'S - 0-3 61-5 16-4 91-5 121-5 49-7 2-0 -16-7 32-0 0-0 62-0 16-7 92-0 33-3 122-0 50-0 2-5 -16-4 32-5 + 0-3 62-5 16-9 92-5 33-6 122-5 50-3 3'O -16-1 0-6 63-0 17-2 33-9 123-0 5O-6 3-5 -15-8 33-5 0-8 63-5 17-5 93-5 34-2 123-5 50-8 4-0 -15-6 34-o i-i 64-0 17-8 94-o 34-4 124-0 5 1 '! 4-5 -15-3 34-5 1-4 64-5 18-1 94-5 34-7 124-5 51-4 5-o -15-0 35-o 1-7 65-0 18-3 95-0 35- I25-0 51-7 u -14-7 -14.4 35-5 36-0 1-9 2-2 65-5 66-0 18-6 1 8-9 95-5 96-0 35-3 35-6 125-5 126-0 51-9 52-2 6-5 -14-2 36-5 2-5 66-5 19-2 96-5 35-8 I26-5 52-5 7-0 -13-9 37-o 2-8 67-0 19-4 97-0 36-1 I27'O 52-8 7-5 -13-6 37-5 3. 1 67-5 19-7 97-5 36-4 127-5 53- i 8-0 - 13-3 38-0 3-3 68-0 20-0 98-0 36-7 128-0 53-3 8-5 -13-1 38-5 3-6 68-5 20-3 98-5 3 6 '9 128-5 53-6 9-0 -12-8 39-o 3-9 69-0 20-6 99-o 37-2 I29-0 53-9 + 9-5 -12-5 + 39-5 + 4-2 + 69-5 + 20-8 + 99-5 + 37-5 + 129-5 + 54-2 ENGLISH INCHES AND MILLIMETRES TABLE XL COMPARISON OF ENGLISH INCHES AND MILLIMETRES, FOR RAINFALL OBSERVATIONS. (01 inch = -254 millimetres.) Inches. Milli- metres. Inches. Milli- metres. Inches. Milli- metres. Inches. Milli- metres. Inches. Milli- metres. 0-05 i-3 2-55 64-8 5-05 128.3 7-55 191-8 II-O 279-4 O-IO 2-5 2-60 66-0 129-5 7-60 193-0 12-0 304-8 0-15 3-8 2-65 67-3 5-I5 I30-8 7-65 194-3 13.0 330-2 O-2O 0-25 2-70 2-75 68-6 69-8 5-20 5-25 I32-I 133-3 7.70 7-75 195-6 196-8 14-0 15-0 355-6 381-0 0-30 7 : 6 2-80 71-1 5-30 134-6 7-80 198-1 16-0 406-4 o-35 8-9 2-85 72-4 5-35 135-9 7-85 199-4 17-0 431-8 0-40 IO2 2-90 73-7 5-40 137-2 7-90 2OO-7 1 8-0 457-2 0-45 II-4 2-95 74-9 5-45 138-4 7-95 201-9 19-0 482-6 0-50 12-7 3-00 76-2 5-50 139-7 8-00 203-2 20-0 508-0 o-55 14-0 3-05 77-5 5-55 141-0 8-05 204.5 21-0 533-4 0-60 15-2 3-10 78-7 5-6o 142-2 8-10 205-7 22-0 558-8 0-65 16-5 3-15 80-0 5-65 H3-5 8-15 207-0 23-0 584-2 0-70 17-8 3-20 81-3 5-7o 144-8 8-20 208-3 24-0 609-6 o-75 0-80 19-1 20-3 3-25 3-30 82-5 83-8 5-75 5-80 146-0 147-3 8-25 8-30 209.5 2IO-8 2|.0 26-0 660-4 0-85 21-6 3-35 85-1 5-85 148-6 8-35 2I2-I 27-0 685-8 0-90 22-9 3-40 86-4 5-90 149-9 8-40 213-4 28-0 711-2 o-95 24-1 3'45 87-6 5-95 I5M 8-45 2I4-6 29-0 736-6 1-00 25-4 3-50 88-9 6-00 I52-4 8-50 215-9 30-0 762-0 . -05 26-7 3-55 90-2 6-05 153-7 8-55 217-2 31-0 787-4 10 27-9 3-60 91-4 6-10 154-9 8-60 218-4 32-0 812-8 15 3-65 92-7 6-15 I56-2 8-65 219-7 33-o 838-2 20 30-5 3-7o 94-0 6- 20 157-5 8-70 22 1 -O 863-6 25 31-7 3-75 95-2 6-25 I58-7 8-75 222-2 35-o 889-0 30 3-8o 96-5 6-30 1 60-0 8-80 223-5 36-0 914.4 35 34-3 3-85 97-8 6-35 161-3 8-85 224-8 37-o 939-8 40 35-6 3-90 99-1 6-40 162-6 8-90 226-1 38-0 965-2 45 36-8 3-95 100-3 6-45 163-8 8-95 227-3 39-o 990-6 38-1 4-00 101-6 6-50 165-1 9-00 228-6 40-0 1016-0 55 39-4 4-05 102-9 6-55 166-4 9-05 229-9 41-0 1041-4 60 40-6 4-10 104-1 6-60 167-6 9-10 23M 42-0 1066-8 65 41-9 4-15 105-4 6-65 168-9 9-15 43-o 1092-2 70 43-2 4-20 106-7 6-70 170-2 9-20 233'7 44-o 1117-6 75 44-4 4-25 107-9 6-75 171.4 9-25 234-9 45-o 1143-0 80 457 4-30 109-2 6-80 172-7 9-30 236-2 46-0 1168.4 85 47-0 4-35 110-5 6-85 174-0 9-35 237-5 47-o 1193-8 90 48-3 4-40 ui-8 6-90 175-3 9.40 238-8 48-0 1219-2 95 49-5 4-45 113-0 6-95 176-5 9-45 240-0 49-o 1244-6 2-00 50-8 4-50 II4-3 7-00 177-8 9-50 24I-3 50-0 1270-0 2-05 52-i 4-55 115-6 7-05 179-1 9-55 242-6 51-0 1295-4 2-IO 53-3 4-60 116-8 7-10 180-3 9-60 243-8 52-0 1320-8 2-15 54-6 4-65 118-1 181-6 9-65 245-1 53-o 1346-2 2-20 55'9 4-70 119-4 7-20 182-9 9-70 246.4 54-o 1371-6 2-25 57-i 4-75 120-6 7-25 184-1 9-75 247-6 55-o 1397-0 2-30 58-4 4-80 121-9 7-3 185-4 9-80 248-9 56-0 1422-4 2-35 59-7 4-85 123-2 7-35 186.7 9-85 250.2 57-o 1447-8 2-40 61-0 4-90 124-5 7-40 188-0 9.90 25I-5 58-0 1473-2 2-45 62-2 4-95 125-7 7-45 189-2 9-95 59-o 1498-6 2-50 63-5 5-00 127-0 7-50 190-5 10-00 254-0 60-0 1524-0 HINTS TO METEOROLOGICAL OBSERVERS TABLE XII. CONVERSION OF ENGLISH MILES PER HOUR INTO METRES PER SECOND. Miles Metres Miles Metres Miles Metres Miles Metres Miles Metres Hour. per Second. Hour. per Second. H P o 6 ur. per Second. H^ur. per Second. H P C ur. per Second. I 0-45 II 4-92 21 9-39 31 13-86 41 18-33 2 0-89 12 5-36 22 9-83 32 I4-3I 42 18-78 3 1-34 13 5-81 23 10-28 33 1475 43 I9-22 4 179 H 6-26 24 iQ-73 34 15-20 44 19-67 5 2-24 15 6-71 25 11-18 35 I5-65 45 20-12 6 2-68 16 7-iS 26 11-62 36 16-09 46 20-56 7 3-13 17 7-60 27 12-07 37 16-54 47 21-01 8 3-58 18 8-05 28 12-52 38 16-99 48 21-46 9 4-02 19 8-49 29 12-96 39 17-43 49 2I-9O 10 4-47 20 8-94 30 13-4I 40 17-88 50 22-35 TABLE XIII. CONVERSION OF METRES PER SECOND INTO ENGLISH MILES PKR HOUR. Metres Miles Metres Miles Metres Miles Metres Miles Metres Miles per Second. H^ur. per Second. fiiour. per Second. H^ur. per Second. Hour. per Second. per Hour. I 2-24 II 24-61 21 46-98 31 69-35 41 9I-72 2 4-47 12 26-84 22 49-21 32 7I-58 42 93-95 3 6-71 !3 29-08 23 51-45 33 73-82 43 96-19 4 8-95 14 3I-32 24 53-69 34 76-06 44 98-43 5 11-18 15 33-55 25 55-92 35 78-29 45 100-66 6 I3-42 16 35-79 26 58-I6 36 8o-53 46 102-90 7 15-66 17 38-03 27 60-40 37 82-77 47 105-14 8 17-90 18 40-27 28 62-64 38 85-01 48 107-37 9 20-13 19 42-50 29 64-87 39 87-24 49 109-61 10 22-37 20 44-74 30 67-II 40 89-48 50 111-85 SPECIMEN OF A CLIMATOLOGICAL RETURN TABLE XIV. SPECIMEN OF A CLIMATOLOGICAL RETURN. ROYAL METEOROLOGICAL SOCIETY. CLIMATOLOGICAL OBSERVATIONS at 9 a.m. (Local Time) made at Hodsock Priory, Worksop, during July 1905. Height above Sea Level, 56 feet. Thermometers 1 1 Earth Thermometers. (Corrected). O || (Corrected). Date. "o Rain. Remarks. Dry. Wet. Max. Min. | CJ i Ft. 2 Ft. 4 Ft. O-IO in. hrs. [T 12 p. 1 57-o 56-8 67-4 55-0 10 34 0-6 60- 1 59-5 56-5 @ 2 5 a, 9 a- 1 p, cloudy p, 2 63-0 59-7 73-3 57-o 6 6-6 60-6 59-o 56-4 Cloudy a, overcast p. 3 64-4 57-i 68-6 56-0 7 6-1 61-6 59-6 56-3 Cloudy. 4 55-2 70-5 42-5 3 7-0 60-3 597 56-6 Fine, cloudy. 5 65-1 58-9 71-9 45'4 7 6-4 60-2 59-5 5^7 Cloudy. 6 63-5 557 69-4 48-5 2 "5 60-9 59-4 5 6-7 Cloudy, fine. 7 66-5 80-0 45'9 O 14-6 60-6 59-4 5 6-7 Very bright. 8 68-7 60-7 79-9 46-3 15-1 61-8 597 5 6-7 Very bright. 9 69-6 63-0 80-9 47-3 O 35 8-8 62-9 60- 1 5 6 '9 Bright a, ] p. 10 69-9 65-5 78-8 56-2 8 5-6 63-1 60-3 57-o Fine, cloudy, dull evening. 11 71-0 65-0 79-3 58-9 3 02 5-2 63-8 60-8 57-2 Fine early, cloudy, 7 p. 12 69-0 63-4 79-9 62-0 10 3-9 64-1 61-0 57-4 Fine, cloudy, T p. 13 72-2 67-4 79-0 66-0 7 8-1 64-7 61-3 57-6 Fine, cloudy. 15 65-7 64-4 83-5 78-6 54-5 58-7 8 13-5 7-2 64-8 61-6 65-4 62-2 57-8 58-1 Very fine and bright. Fine, cloudy. 16 63-4 57-4 71-5 54-7 9 5-5 64-5 62-4 58-3 Fine, cloudy. 17 60-0 54-4 68-8 10 09 2-6 63-3 62-0 58-4 ! Cloudy a, dull p. 18 68-4 62-3 75-5 55-8 6 7-4 63-1 61-6 58-6 i a, fine, cloudy p. 19 65-6 56-8 747 44-3 i 10-4 63-0 61-5 58-4 Bright a, cloudy p, fine night. 20 7i-3 62-3 75-4 47-2 7 6-5 63-0 61-4 58-5 Bright a, cloudy, hazy p. 21 7M 64-! 79-7 56-0 ! 6-5 63-1 61-2 58-5 Fine, cloudy. 22 68-4 62-5 75-2 52-6 10 08 1-6 63-1 61-2 58-4 Cloudy. 23 637 60-3 7o-3 597 8 03 1-6 637 61-3 58-4 3 a, overcast, 8 p. 24 63-3 58-0 50-7 5 1 1.6 63-2 61-2 58-5 Fine. 25 69-7 63-3 77 : 8 58-7 2 10-8 63-5 6i-3 58-6 Fine day, overcast night. 26 63-0 59-3 70-6 55-2 IO 37 o-5 63-8 617 58-6 Overcast, a, 2 evening. 27 63-6 59-9 7 I- 5 57-3 8 4-6 63-0 61-6 58-7 Cloudy, fine night. 28 64-1 56-1 70-9 48-0 i OI 7-6 62-1 61-5 58-7 Cloudy, fine. 29 59-5 58-5 68-6 48-2 10 02 62-0 61-3 587 Overcast, , fine evening. 30 57-2 69-9 56-3 7 4-5 61-6 60-9 587 Cloudy. 31 6*3 55-8 67-3 47-9 6 61-0 60-8 58-6 Overcast, fine night. Sums 187-0 5-8 133-8 94-5 172 i-3i 208-1 81-9 26-0 24-2 Means 66-0 60-2 74-3 53-o 5-5 Sunless Days. 62-6 60-8 57-8 Corrections for Index Errors. Appl ied da ily. i Means Corrected. Highest Temperature (corrected) 83- 5 on I4th. Lowest Temperature (corrected) 425 on 4th. Mean Temperature .... 637 Mean Range of Temperature Relative Humidity . No. of Rainy Days . 21-3 69% 9 (Signed) HENRY MELLISH. (It is requested that this Form be returned unsealed by the loth of the month following that to which it belongs. ) E A GLOSSARY OF METEOROLOGICAL TERMS Absolute Temperatures. These are degrees Centigrade above the absolute zero -273 C. Thus 273 A., o C., and 32 F. all correspond with the freezing- point of water. Accumulated Temperature. This is the combined amount and duration of the excess or defect of the air temperature above or below the base temperature of 42. It is considered that the tempera- ture above that value is mainly effectual in starting and maintaining the growth and in completing the ripening of agri- cultural crops. [DE CANDOLLE.] Actinometer. An instrument for measur- ing the intensity of solar radiation. [HERSCHEL, 1826.] Adiabatic. Changes which occur in the pressure, volume, and temperature of a mass of gas, which is subject to the condition that it neither parts with, nor receives, heat during the process, are said to be "adiabatic." Advective Region. See Stratosphere. (Ad- vektion is also used by Zenker to denote the difference between actual and " solar " temperature. ) [GOLD, 1909.] After-glow. The radiance or glow seen in the western sky for a longer period than usual after the sun has set. Alto-Cumulus. See Clouds, p. 32. Alto-Stratus. See Clouds, p. 32. Anemo-ciuemograph. An instrument for recording the velocity of the wind each second. Anemo - clinograph. An instrument for recording the angular deviations of wind movement from a horizontal path, or from one parallel to the surface of the ground. Anemogram. The trace marked on paper by an anemograph. Anemograph. A self-recording anemometer. Anemometer. An instrument for measur- ing the pressure or velocity of the wind. Anemoscope. An instrument for recording the direction of the wind. Aneroid. An instrument consisting essen- tially of an elastic metal box, exhausted of air, which indicates on a dial the changes due to variations of external pressure on the box, and therefore act- ing as a barometer. [ViDi, 1848.] Aneroidograph. A self-recording aneroid barometer. Anthelion. Coloured rings seen round the shadow of an observer, projected on to a cloud or fog lying below him. Also called "Glory." Anticyclone. An area of relatively high barometric pressure increasing towards the centre, in which the wind blows spirally outwards, and in the northern hemisphere, in the direction of the move- ment of the hands of a watch. [GALTON, .1863.] Anticyclonic Belts. These belts are com- posed of the successive so-called per- manent anticyclonic systems of the atmosphere, between the trade winds and the circulation of temperate latitudes. Anti- Trades. Winds circulating on the Polar sides of the Trade -winds, the prevailing directions being South-west in the northern hemisphere and North- west in the southern hemisphere. [HERSCHEL, 1862.] Aqueous Vapour. See Elastic Force of Vapour. Arched Squall. A squall off the west coast of Africa, in which the clouds take the shape of an arch. Aspiration Psychrometer. The dry - bulb and wet - bulb thermometers with a special contrivance for passing a current of air of definite velocity over the bulbs. [ASSMANN, 1884.] Atmometer. An instrument for measuring the amount of evaporation of water. Atmospheric Pressure. Pressure produced by the weight of the air. Audibility. Unusual distinctness of distant sounds. Aurora Australis. A luminous electrical display of much beauty appearing in the sky in the southern hemisphere, some- times taking the form of an arch, streamers, corona, glow, etc. Aurora Borealis. A similar display to the Aurora Australis, only appearing in the northern hemisphere. 66 A GLOSSARY OF METEOROLOGICAL TERMS Average. See Mean. Azimuth. The angle which the vertical, plane passing through an object makes with the plane of the meridian. Backing- Wind. A wind which changes in a direction contrary to that of the sun's apparent course, as^. from W. through S. to E., etc. Baguio. The Philippine name for a re- volving storm or cyclone. Bai-U. The rainy season in japan during the latter half of June and the first half of July. It means the "plum rain season," as it comes when the plums are getting ripe. Ball Lightning. A luminous ball or globe which moves slowly and some- times bursts, giving rise to flashes of lightning. Ballon Sonde. A small, free rubber balloon employed for raising a meteorograph to obtain a record of the conditions pre- vailing in the upper regions of the atmosphere. Balneology. The science or study of mineral springs and baths. Barocyclonometer. An instrument for ascertaining the position, distance, and direction of advance of a cyclone or revolving storm. [ALGUE, 1898.] Barogram. The trace marked on paper by a barograph. Barograph. A self-recording barometer. Barometer. An instrument for measuring the pressure of the atmosphere. [BOYLE, 1665.] Beaufort's Scale. Devised by Admiral Sir F. Beaufort, and now in general use for estimating the force of the wind. [See p. 26.] Bize. A cold, piercing wind of Languedoc. Blackthorn Winter. The cold weather, accompanied by keen North-east winds, which sometimes occurs about the second week in April, when the blackthorn is in bloom. Blizzard. A violent and bitterly cold wind accompanied with blinding snow. Blood Rain. See Red Rain. Bloxamize. The method adopted by Mr. T. C. Bloxam to obtain smoothed mean values. [1858.] Bora. A violent, cold, anticyclonic wind, blowing down from mountains close to the coast, if a chilled tableland lies behind them. The Bora of the Adriatic is best known, but a similar wind is observed elsewhere. Breezes, Land and Sea. Winds which blow- near the coast, from sea to land during the day, and from land to sea during the night. Brickfielder. A very hot, dust-laden wind blowing from the North in New South Wales. Brocken Spectre. See Anthelion or Glory. Brontometer. An instrument to show the sequence of the various phenomena occurring during thunderstorms. [SYMONS, 1890.] Buran. Gale from the North-east, accom- panied with drifting snow, in the Steppes of Central Asia. See Purga. Burst of the Monsoon. The sudden change of weather accompanying the setting in of the South-west Monsoon. Buys-Ballot's Law. In the northern hemi- sphere, "Stand with your back to the wind and the barometer will be lower on the left hand and higher on the right." [Directions are reversed in the southern hemisphere.] [Buvs BALLOT, 1860.] Calm. A quiescent state of the air. Calm Belt. See Doldrums. Calm Centre. The vortex of a cyclonic storm. Cape Doctor. The name given to the cool Southerly gales which often blow in summer at Cape Town. Centigrade. The thermometer scale, fre- quently called after Celsius, in general use on the Continent, in which the interval between the freezing and boil- ing points is divided into 100, the freezing-point being o and the boiling- point 1 00. Centres of Action of Atmosphere. The term includes the so-called permanent anticyclonic belts of the atmosphere as well as the well-defined and somewhat durable cyclonic systems. [Some writers make a distinction between the centres of action of the atmosphere and the centres of action of individual anti- cyclonic or cyclonic systems.] [TEISSERENC DE BORT, 1881.] Chinook. A warm, dry wind at the eastern base of the Rocky Mountains, similar to the Fohn. Cirro-Cumulus. See -Clouds, p. 32. Cirro- Stratus. See Clouds, p. 32. Cirrus. See Clouds, p. 31. Climate. The average condition of meteoro- logical phenomena at a given place. Climatological Station. A station at which observations are made only once a day, usually at 9 a.m. [TRIPE, 1879.] Climatology. The science or study of climate. Cloud. Moisture in the air condensed into a visible form. [For names of clouds, see p. 32.] Cloud -Burst. Sudden precipitation of a great amount of rain or hail in a short time. Col. A neck of low pressure between two anticyclones. [ABERCROMBY, 1882.] Comozants. See St. Elmo's Fire. Convective Region. See Troposphere. [GOLD, 1909.] Corona. A series of small coloured rings, due to refraction through thin clouds, round the sun or moon. The order of the colours is the reverse of that in the rainbow. Corposants. See St. Elmo's Fire. Crepuscular Rays. Diverging beams seen when the . sun is near the eastern or western horizon, and clouds are gathered round its disc. E 2 68 HINTS TO METEOROLOGICAL OBSERVERS Cumulo - Nimbus. Thunder cloud. See Clouds, p. 32. Cumulus. Wool-pack cloud. See Clouds, p. 32. Cyclone. An area of relatively low baro- metric pressure, decreasing towards the centre, in which the wind blows spirally inwards, and in the northern hemisphere, in the opposite direction to the movement of the hands of a watch. The name is usually applied to tropical revolving storms. [PiDDiNGTON, 1839.] Day Degree. The accumulated temperature is expressed in " Day Degrees" a day degree signifying i of excess or defect of temperature above or below 42 continued for 24 hours, or any other number of degrees for an inversely proportional number of hours. [STRACHEY, 1881.] Depression. See Cyclone. Dew. Condensation of moisture on solid objects caused through cooling by radia- tion. Dew-Point. The temperature at which dew begins to be deposited. Diathermancy. The property in virtue of which the solar rays pass through a medium without raising its temperature. Diurnal Inequality or Diurnal Variation. Changes due to the time of day. Diurnal Range. The amount of variation between the maximum and minimum of any element during the 24 hours. Doldrums. The belt of calms near the equator. Drizzle. Rain in very small drops. Drought. A long continuance of dry weather. Absolute Drought, a period of 15 or more consecutive days absolutely with- out rain. Partial Drought, a period of 29 or more consecutive days the aggregate rainfall of which does not exceed o-oi in. per diem. [SYMONS, 1887.] Dust -Counter. An instrument for counting the number of dust particles in a given volume of air. [AiTKEN, 1889.] Dust-Storni. A whirlwind passing over a dry or sandy district and carrying up the dust into the air. Dynamic Cooling. The cooling produced by the expansion of air when it passes into a region of decreased pressure. Dynamical Meteorology. This deals with the motions of the atmosphere, their causes, and the conditions arising there- from, and also of the modification which these motions produce in the statical conditions. Elastic Force of Vapour. Pressure of the water vapour in the atmosphere. Electrometer. An instrument for measuring the electrification of the air. Error of Capacity. The error in the height of a mercurial barometer arising from the change of level of the mercury in the cistern. Etesian Winds. Northerly winds which pre- vail in summer over the Mediterranean. Evaporation. The process of vapour passing into the air from water and moist surfaces. Evaporimeter. An instrument for measur- ing the amount of evaporation. Eye of the Storm. The vortex or calm centre of a tropical revolving storm. Fahrenheit. The thermometer scale in gen- eral use in English-speaking countries, in which the interval between the freez- ing and boiling points is divided into 1 80, the freezing-point being 32 and the boiling-point 2 1 2. [FAHRENHEIT, 1714.] Five-Day Means. Frequently employed on the Continent, by which the year is subdivided into 73 pentads or periods of 5 days each. Flood. An inundation caused by heavy rain- fall or the overflow of a river. Fog. A cloud in contact with or close to the ground. Fog- Bow. White rainbow seen on a thick fog. Fb'hn. A warm, dry wind descending from the mountains, most frequent in Alpine valleys, and elsewhere in mountainous districts. It owes its dryness to the circumstance that the air is descending from a mountain ridge, and is warmed by compression in its descent. Forked Lightning. The branched or sinuous flashes of lightning. Freezing -Point. The temperature at which water freezes or ice melts viz. 32 Fahrenheit, o Centigrade, and o Reaumur. Fulgurites. Silicious tubes of various sizes, vitrified internally by lightning striking the ground and fusing the sand. Gale. Strong wind with a minimum velocity of over 39 miles an hour. Glazed Frost. The coating of ice produced either by a frost setting in after a partial thaw, or by rain falling during hard frost and congealing as it falls. Globular Lightning. See Ball Lightning. Gloom. The darkness occasioned by a dense pall of cloud. Glory. Coloured rings seen round the shadow of an observer, projected on to a cloud or fog lying below him. (Also called " Anthelion.") Gradient. The difference in pressure, tem- perature, or other meteorological element per unit of distance. [STEVENSOX, 1867.] Graupel (German). Soft hail. Green Eay. A flash of greenish-blue light seen, when the sun's disc appears or disappears, in a sunrise or sunset on a clear horizon. Gregale. A cold, dry, unhealthy, North- easterly wind blowing over Malta in spring and early summer. Gresil (French). Soft hail. Ground Frost. This is taken to be when the minimum thermometer exposed on the grass falls to 30 or below that point [3O-4 if the thermometer is read to tenths of a degree]. Haar. The name given to a sea - fog A GLOSSARY OF METEOROLOGICAL TERMS 69 accompanying an Easterly drift of air on the east coast of Britain. The pheno- menon is more common in the Firth of Forth than elsewhere. Hail. Frozen rain. Large hailstones some- times consist of alternate deposits of hoar-frost and ice. Halo. Large circle of coloured light sur- rounding the sun or moon, commonly of about 44 in diameter. Harmattan. Hot Easterly wind on the west coast of Africa. It is loaded with red dust. Haze. Obscuration of the atmosphere pro- duced by the presence of dust particles. Helm- Wind. A violent, cold Easterly wind blowing down the western slope of Crossfell, Cumberland. High, A. A term used mostly in America to denote an anticyclone or high-pressure system. High-Pressure System. See Anticyclone. Hoar-Frost. Frozen dew. Humidity. See Relative Humidity. Hurricane. The name usually applied to the tropical revolving storms which visit the West Indies and the islands of the South Pacific. Hyetograph. A self-recording rain gauge. Hyetometry. The determination of the amount of water condensed out of the atmosphere in the form of rain, hail, or snow. Hygrograph. A self-recording hygrometer. Hygrometer. An instrument for measuring the humidity of the air. [LAMBERT.] Hygrometry. The determination of the amount of water present in the air in a vaporous form. Hypsometer. A thermometer for measur- ing altitudes by the lowering of the boiling-point of water consequent upon the reduction of atmospheric pressure at high altitudes. Index Error. The error made in laying off the scale of an instrument. Indian Summer. Fine weather for a few days about September 30, in North America. Insolation. Solar radiation. Inversion of Temperature. A warmer stratum of air above a colder one. Invierno. The rainy season in tropical America. Ion. Any minute material particle which carries an electrical charge. lonisation. The process by which ions are produced. Iridescent Clouds. The under -surface of cirrus or cirro-cumulus clouds illumi- nated with rings or patches of iridescent colours. Isabnormal Lines. Lines drawn through places having the same anomaly, e.g. the same difference between the actual mean temperatures and the theoretical mean temperatures for places in a given latitude. [DOVE, 1852.] Isanakatabars. Lines of equal pressure amplitudes. [SHAW, 1909.] Isobars. Lines on maps showing equal atmospheric pressure. [RENOU, 1864.] Isobrontal Lines. Lines on maps showing equal times or hours of thunderstorms. Isohels. Lines on maps showing equal amounts of bright sunshine. Isohyets. Lines on maps showing equal amounts of rainfall. Isonephs. Lines on maps showing equal amounts of cloudiness. Isopleths. This strictly should include isobars, isotherms, or other form of " iso " lines ; in practice it is applied to diagrams which express the variation of hourly values throughout the year. Isothermal Layer. A term often used to denote the upper region of the atmo- sphere in which the temperature changes very little with altitude. [TEISSERENC DE BORT, 1899.] Isotherms. Lines on maps showing equal temperatures. [HuMBOLDT, 1817.] Khamsin. Hot, dry wind of Egypt, supposed to last for 50 days at a time. Killing Frost. A term used in America to denote a frost sufficiently severe to be injurious to vegetation. Kilometre. 0-62 mile (a mile is 1-61 kilo- metre). Kite. The form most used in meteorology is the Hargreave or box-kite, and it is employed for raising a meteorograph to obtain a record of the conditions pre- vailing in the upper regions of the atmosphere. Lammas Floods. A term used to denote a wet period about the first week in August. Land Breeze. See Breezes. Larry. A local name for a dense sea-fog at Teignmouth, Devon. Lenticular Cloud. A cloud which assumes an ovoid or flat spheroid form with sharp edges. Leste. Hot, dry, dust -bearing wind of Madeira. It blows from between North - east and South-east. Levanter. See Solano. Leveche. The Spanish name for the Scirocco. Lightning. Disruptive discharge of elec- tricity during thunderstorms. Lightning Conductor. A mode of protec- tion against lightning. Line Squalls. The line of squalls which are associated with the trough of a cyclone or V-depression. [ABERCROMBY, 1884.] London Fog. The dry, gloomy, irritating fog peculiar to London and other large towns, aggravated by smoke. Low, A. A term used mostly in America to denote a cyclone or low-pressure system. Low-Pressure System. See Cyclone. Lunar Halo. See Halo. Lunar Rainbow. See Rainbow. Mackerel Sky. Cirro-cumulus clouds. Mares' Tails. Long, wispy, cirrus clouds. Mean. The arithmetical average or mean is the sum of all the values forming the series of figures under consideration divided by their number. Average is the HINTS TO METEOROLOGICAL OBSERVERS term used for results extending over a long period, while Mean is used for short periods, e.g. a day, month, or year. Meniscus. The convexity of the mercury in the barometer tube. Meteorograph. An instrument for recording the changes of pressure, temperature, humidity, etc. , on one sheet of paper. Meteorology. The science of the atmo- sphere. Metre. 39-37 inches (an inch is -025 metre). Metre per Second. 2-24 miles per hour (a mile per hour = -45 metre per second). Micro-Barograph. A very sensitive stato- scope which combines the recording of variations of atmospheric pressure upon a magnified scale with the practical obliteration of the general surges through the operation of a small leak. [WHITEHOUSE, 1871.] Millimetre = 0-03 9 inch. Mirage. An appearance produced by the successive bending of rays of light in passing through strata of air of varying densities. Mist. A cloud in contact with the ground, wetting objects exposed to it. Mistral. A violent, cold, dry North-westerly wind, of similar origin to the Bora, which sweeps the shores of the Gulf of Lyons. Mock Suns and Moons. Bright patches of light seen at the points where the vertical or horizontal bands of light from the sun or moon intersect a halo. Monsoons. Periodical winds blowing from sea to land in summer, and from land to sea in winter. The South- west or summer Monsoon, and the North-east or winter Monsoon of India, China, and the neighbouring seas, are the best known examples. Nephoscope. An instrument for observing the direction and rate of motion of clouds. Nimbus. Rain cloud. See Clouds, p. 32. Noah's Ark. A cloud formed by stripes of cirrus which (owing to perspective) appear to coalesce at opposite points of the horizon. Northers. Dry, cold winds over the Gulf of Mexico. Similar winds at Valparaiso have the same name. Nor'-Westers. The fohn - like dry warm winds which blow east of the mountains of the middle island of New Zealand. Ombrometer. A rain gauge. Ozone. An exceptionally active condition of oxygen. Pampero. A sudden cold, squally, Southerly wind blowing in the rear of a low-pres- sure system over the pampas of Argen- tina, and in the neighbourhood of the River Plate. Paraselenae. Mock-moons. Parhelia. Mock-suns. Peg-top Sunset. When the sun is setting over the sea it sometimes assumes the shape of a peg-top owing to refraction. Pentad. A period of five days. Percolation. The penetration of rain into the soil. Periodical Variations. The variations which recur at regular intervals, such as a day or a year. Phenology. A term indicating the ob- servation of natural periodical pheno- mena, such as the flowering of plants, the migration and song of birds, etc. [1874-] Pilot Balloon. A small free balloon employed for ascertaining the drift and the velocity of the upper currents of the atmosphere. Pluviograph. A self-recording rain gauge. Pluviometer. A rain gauge. Pocky Cloud. The base of a cumulus cloud when it assumes a festooned appearance. Ponente. A Westerly wind in the Mediter- ranean. Pressure Plate. A form of anemometer for registering the pressure of the wind. Pressure Tube. A form of anemometer by which the force of the wind is measured. [DiNES, 1892.] Prognostics. Premonitory signs of good or bad weather. Psychrometer. The dry- bulb and wet-bulb thermometers. [AUGUST, 1825.] Pumping of Barometer. Unsteadiness of the mercury in the barometer tube caused by the temporary reduction of pressure in a room, produced by gusts of wind. Punos. Intensely cold, dry winds in the Puna regions of South America, blowing chiefly from South and South-west. Purga. A very violent Buran (which see). Pyrheliometer. An instrument for measur- ing the intensity of solar radiation. [POUILLET, 1856.] Radiation. The interchange of heat between bodies which are not in contact. Rain. Condensed moisture which falls from the clouds in a liquid form. Rainband. A dark band or shading seen on the red side of the double line D in the atmospheric absorption spectrum. Rainbow. An arc of prismatic colours seen opposite the sun or moon when rain is falling. Rainfall. This term includes all forms of atmospheric precipitation. Rain Gauge. . An instrument for measuring rainfall. Rainy Day or Rain Day. This is defined in the British Isles to be a day on which o-oi inch, or more, of rain is recorded. [SYMONS, 1862.] Reaumur. The thermometer scale formerly in use in Germany and Russia, but now abandoned officially, in which the interval between the freezing and boiling points is divided into 80 ; o is at the freezing- point. [REAUMUR, 1730.] Red Rain. Rain charged with dust carried often for great distances from sandy deserts. Registering Balloon. See Ballon Sonde. Relative Humidity. The ratio or percentage A GLOSSARY OF METEOROLOGICAL TERMS of the actual vapour pressure to that of saturated water vapour at the temperature of the air. Ridge. A high -pressure area between two contiguous areas of low pressure. Rime. Frozen moisture on trees, etc., resembling thick hoar-frost. It occurs mostly during fog. Roaring Forties. The regions between lat. 40 and 50 S., where the " brave West winds " blow. St. Elmo's Fire. A luminous, electrical dis- play, similar to the brush-discharge of an electrical machine, visible at night at the extremities of pointed objects, such as mast-heads and yard-arms of ships, tops of trees, etc., during unsettled weather. St. Luke's Summer. A period of fine, quiet weather about the middle of October. St. Martin's Summer. A period of excep- tionally mild, quiet weather in November. Saturation. The condition of the air when fully charged with moisture. Scotch Mist. The name given to the fine rain or drizzle which is of frequent occurrence in hilly country. Scud. Fragmental clouds driven along by stormy winds beneath heavy clouds. Sea-Breeze. See Breezes. Second Order Station. A station at which observations are made at least twice a day, usually at 9 a.m. and 9 p.m. Secondary Cyclone. A small depression accompanying a larger or primary cyclone. Seismograph. An instrument for recording earth-tremors or earthquakes. Serein. Fine rain falling from a cloudless sky. Sheet Lightning. The reflection of distant flashes of lightning. Silver Thaw. The phenomenon of a large quantity of frozen moisture on trees, walls, etc. , sometimes consisting of ice, but more frequently crystallized and presenting a beautiful snow-like appear- ance. Simoom. A hot, suffocating wind, bearing clouds of sand, in the Sahara. Sirocco. A hot South-east wind blowing from the heated Sahara, dry on the coast of Africa, but moist on the coast of Europe. Sleet. A mixture of snow and rain. Sling Thermometer. A thermometer tied to a string and swung round the head to determine the temperature of the air. Readings obtained in this manner, even in full sunshine, agree very closely with the true shade temperature. [ARAGO.] Snow. Minute crystals of water, the crystals being hexagonal or six-pointed. Snow Rollers. Cylinders of snow formed and driven along by the wind, something like a lady's muff. Soft Hail. Pyramidal soft pellets of ice, like miniature snowballs, which fall in cold weather in spring. Soft place in the Monsoon. A tract in the North Indian Ocean between the Equator and 9 N., and between Cloney and Socotra, where the Monsoon is weaker than elsewhere. Solano. The East wind in Spain. Solar Halo. See Halo. Solar Radiation. The term used for heat which is received from the sun. Southerly Burster. A sudden strong, cool, rain-bringing South wind in the rear of a low-pressure system in Australia. Squall. A sudden, short storm of gusty wind. Statoscope. An instrument consisting of a series of very sensitive metal boxes (some- thing like the vacuum boxes of an aneroid) contained in a hermetically- sealed reservoir which is placed in a box thickly surrounded by wool, to prevent the disturbing influence of change of temperature. A very sensitive form of barometer. Stephanome. An instrument for measuring the angular size of halos, fog-bows, glories, etc. [TAIT.] Storm. A violent commotion of the atmo- sphere. Strato-Cumulus. See Clouds, p. 32. Stratosphere. Set Isothermal Layer. [TEISSERENC DE BORT, 1908. Stratus. See Clouds, p. 33. Sulphur Rain. A deposit of the pollen of pine trees often carried by wind for long distances and brought down by rain. Sultry. Hot and close condition of the atmosphere. Sun-Dogs. Mock-suns. Sunless Day. A day on which the duration of sunshine is less than 3 minutes. Sun Pillar. A perpendicular column of light, of the breadth of the sun's disc, seen projecting upwards from the sun about the time of sunrise or sunset. Sunshine Recorder. An instrument for re- cording the duration of bright sunshine. Sympiesometer. An instrument formerly in use for showing the variations of atmospheric pressure. Its indications result partly from the pressure and partly from the temperature of the atmosphere. [AniE, 1819.] Synoptic Chart. A map showing, by means of isobars, isotherms, etc., the general distribution of atmospheric conditions over a considerable area. Temperature. The slate of a body with regard to heat. Tension of Vapour. See Elastic Force of Vapour. Terrestrial Radiation. The term used for heat which is given out from the Earth. Thermogram. The trace marked on paper by a thermograph. Thermograph. A self-recording thermo- meter. Thermometer. An instrument for measuring the temperature. [BACON, 1587.] Thermometer Screen: A louvre-boarded box for protecting the thermometers from the sun's rays and also from rain. [STEVENSON.] Thermometre Fronde. See Sling Thermo- meter. HINTS TO METEOROLOGICAL OBSERVERS Thermo -sychropherus. An apparatus for illustrating the cooling effect by the communication of heat under certain conditions to a mass of air in the free atmosphere. [SHAW, 1905.] Thunder. The noise heard after the dis- charge of lightning. Thunderstorm. An atmospheric disturb- ance accompanied by lightning, thunder, and frequently hail. Tornado. Originally a severe squall on the coast of Senegambia and Guinea, but of late years applied to whirlwinds on shore. Tornado Cloud. A funnel-shaped cloud which accompanies violent and destruc- tive tornadoes, and most frequent in the United States. Trade-Winds. Constant winds which blow towards the Equator from the North- east and South-east between the latitudes of about 30 N. and 30 S. [HALLEY, 1686.] Trajectory of Air. The supposed path taken by a definite mass of air in a travelling storm. [SHAW, 1903.] Tramontana. A general name for Northerly winds in Italy. Troposphere. The lower region of the atmosphere in which the temperature falls rapidly with increasing altitude. [TEISSERENC DE BORT, 1908.] Trough. The line of lowest barometer readings during the passage of a cyclone, at right angles to its path. Tule Fog. The term used in California to denote fogs over marshes and swamps, or the fogs of the lowlands and the valleys. Typhoon. A violent revolving storm in the China Seas and Eastern Pacific. Upbank Thaw. A rise of temperature with height during severe frost, when the cold air collects in the valleys, while the adjacent summits are warmed by the descending air from the centre of an anticyclone. V-Depression. A low-pressure area between two contiguous areas of high pressure. [ABERCROMBY, 1882.] Vapour Tension. See Elastic Force of Vapour. Vector Diagram. A wind diagram traced out by a vector which represents the wind by its length and direction. Veering-Wind. A wind which changes in the same direction as the apparent course of the sun, i.e. from E. by S. to W. , etc. Velocity of Wind. The rate at which the wind travels in miles per hour. Vendavales. South-west winds in the Straits of Gibraltar very troublesome to naviga- tion ; the term is also used for Westerly winds in New Granada. Veranillo. The short, dry season near mid- summer in tropical America. Verano. The long, dry season near mid- winter in tropical America. Vernier. A small movable scale for taking minute readings, attached to instruments. Visibility. Unusual clearness of distant objects. Vortex. The calm centre of a cyclonic storm. Waterspout. A whirlwind passing over the sea, in which a spout or trunk is formed, joining the cloud and sea. Weather. The condition of the atmosphere at any moment with regard to wind, temperature, cloud, moisture, and precipitation. Weather Forecast. A prediction of coming weather based on meteorological observa- tions. [FlTZROY.] Wedge. See Ridge. [ABERCROMBY and MARRIOTT, 1882.] Whirlwind. A small local cyclonic whirl in which there is a very strong upward motion of the air. White Frost. See Hoar Frost. White Squall. A sudden squall of wind which only becomes visible through the commotion on the sea surface, which is lashed up into white spoon-drift. Williwaws. Sudden violent squalls in the Straits of Magellan. Willy Willy. The name applied to a cyclone in Western Australia. Wind. Air in motion. Wind Eose. A diagram showing the pro- portions of winds observed from each point of the compass. Wind Vane. An instrument employed for showing the direction of the wind. Zonda. A wind of the sirocco type blowing in the pampa of Argentina. 1 ROYAL METEOROLOGICAL SOCIETY THE Society was founded for the promotion of the Science of Meteorology in all its branches on April 3, 1850, under the title of "The British Meteorological Society." On its incorporation by Royal Charter on January 27, 1866, the name was altered to "The Meteorological Society"; and in 1883, by permission of Her late Majesty QUEEN VICTORIA, it became " THE ROYAL METEORO- LOGICAL SOCIETY." It is now under the distinguished Patronage of His Majesty KING GEORGE V. Meetings are held on the third Wednesday in each month from November to June inclusive those in the evening being usually (by permission) at the Institution of Civil Engineers, Great George Street, and those in the afternoon in May and June at the Society's Rooms, 70 Victoria Street, Westminster. These occasions afford an opportunity for social intercourse between those interested in Meteorology, tea being served after the evening meetings or before the meetings in the afternoon. Popular Lectures on meteorological subjects by eminent authorities are arranged for on special occasions. Exhibitions of new and of special classes of meteorological instruments, as well as of diagrams, charts, and photographs, are also held from time to time. The Papers read at the Meetings, together with the Discussions, in which every Fellow is entitled to take part, are printed in the Quarterly Journal, which also contains Notes, Correspondence, Notices of Recent Publications, and the titles of such papers as appear to be of general interest bearing on Meteorology in the periodicals which are received in the Society's Library. It thus serves to keep Fellows residing at a distance from London in touch with the meteorological work of the world. In 1874 tne Society commenced the organisation of a series of 73 74 HINTS TO METEOROLOGICAL OBSERVERS " Second Order Stations," at which observations of pressure, tempera- ture, humidity, rainfall, and wind are made on a uniform plan, so that the results may be strictly comparable. In addition to these, another class of station, termed " Climatological," was organised on January I, 1880, at which the observations, although of equal accuracy, are less exacting. These stations, which number about 130, are well distributed throughout the country ; they are regularly inspected on behalf of the Society, and the results of the observations are published in the Meteorological Record. In 1874 a Conference on the observation of Periodical Natural Phenomena was organised, and as the result of their deliberations the Society instituted the series of " Phenological Observations " which have been continued since that time, first under the super- intendence of the late Rev. T. A. Preston, and since 1888 under that of Mr. E. Mawley. A Lightning Rod Conference was organised in 1878, which in 1882 published a valuable Report embodying a code of Rules for the erection of Lightning Conductors. The Society has initiated and carried out various scientific investigations, of which the following may be mentioned : (i) Systematic Investigations of the Thunderstorms of 1888 and 1889, and the Classification of the various forms of Lightning ; (2) Inquiry into the Phenomenon of the Helm-Wind of Crossfell, Cumberland ; (3) Investigation into the relation between Beaufort's Scale of Wind Force and the Equivalent Velocity in Miles per Hour ; (4) The Investigation of the Meteorological Conditions of the Upper Air by means of Kites and small Balloons. The SYMONS GOLD MEDAL, founded in 1901, in memory of the late Mr. G. J. Symons, F.R.S., is awarded biennially by the Council for distinguished work done in connection with Meteoro- logical Science. The Medal was presented to Dr. A. Buchan, F.R.S., in 1902 ; to Dr. J. Harm, of Vienna, in 1904 ; to Lieut-Gen. Sir R. Strachey, F.R.S., in 1906 ; to M. L. Teisserenc de Bort, of Paris, in 1908 ; and to Dr. W. N. Shaw, F.R.S., in 1910. The Society possesses a valuable Meteorological Library of about 24,000 books and pamphlets, and about 1000 manuscripts, unequalled by any collection of works on this science in the world. Many of the earlier books are very rare, and in several cases the only known copy in existence is that in the Library. The Society also possesses a unique Bibliography, which contains the titles of all books, pamphlets, papers and articles bearing on Meteorology, of which any notice can be found. This Bibliography is kept up to date, about 5000 entries being added to it every year. In addition to these, there is a large and interesting collection of photographs and lantern slides illustrating meteorological phenomena and instruments. ROYAL METEOROLOGICAL SOCIETY 75 With the view of advancing the general knowledge of Meteorology, and promoting an intelligent public interest in the science, the Council in 1905 appointed Mr. W. Marriott as their Lecturer to act in co-operation with scientific societies, institu- tions, and public schools. Lectures have been given at many of the leading public schools and local scientific institutions in various parts of the country. Exhibitions, instruments, photographs, draw- ings, diagrams, and charts illustrating meteorological phenomena,, are shown, under the charge of a member of the staff, at gatherings of local scientific societies, or on other occasions when they are likely to prove of interest. Candidates for the Fellowship are elected by ballot, after recommendation by three Fellows, one of whom must certify from personal knowledge. Ladies are eligible for the Fellowship. Fellows are entitled to the designation F.R.Met.Soc. Fellows have the privilege of attending the Meetings and introducing visitors ; they have the free use of the Library and receive gratis the Quarterly Journal, the Meteorological Record, and the other publications of the Society. The Council of the Society is elected by the Fellows annually, and reports to the Fellows at the Annual General Meeting. The Library and Offices at 70 Victoria Street, Westminster, are open daily between the hours of 10 a.m. and 5 p.m., excepting on Saturdays, when they are closed at I p.m. Fellows are always welcomed at the Society's rooms, and the Office staff is always ready to assist in supplying any meteorological information which is desired. Every Fellow pays an annual subscription of 2, or a life composition of 25, and in addition an entrance fee of i. For Fellows elected in November and December the payment of the first subscription exempts them from any contribution for the next succeeding year. In addition to the Fellows, there is a class (limited to twenty) of Honorary Members, which is confined to distinguished Meteorologists not resident within the United Kingdom. PUBLICATIONS OF THE /Ifreteoroiogical Society REPORTS OF THE COUNCIL. ist, 1851,10 nth, 1861. Mostly out of print. PROCEEDINGS. Vol. I, 1861-63, to Vol. V., 1869-71. Price >i : 55. each. QUARTERLY JOURNAL. Vol. I, 1872-73, to Vol. XXXVL, 1910. Price 1 each. Quarterly Nos., 53. each. THE METEOROLOGICAL RECORD. Monthly Results of Observa- tions made at the Stations of the Royal Meteorological Society, with Remarks on the Weather for each Quarter. By WILLIAM MARRIOTT, Assistant- Secretary. Price is. 6d. each. (Commenced 1881.) HINTS TO METEOROLOGICAL OBSERVERS. Instructions for taking- Observations, and Tables for their Reduction ; together with a Glossary of Meteorological Terms. By WILLIAM MARRIOTT, Assistant-Secretary. Seventh Edition, Revised and Enlarged. With Illustrations. Price is. 6d. SOME FACTS ABOUT THE WEATHER. A Popular Meteorological Handbook. By WILLIAM MARRIOTT, Assistant-Secretary. Second and Revised Edition. Price 6d. POCKET REGISTER FOR ORIGINAL METEOROLOGICAL OBSERVA- TIONS. Price is. 6d. INSTRUCTIONS FOR THE OBSERVATION OF PHENOLOGICAL PHENOMENA. Second Edition. Price 6d. CATALOGUE OF THE LIBRARY OF THE ROYAL METEORO- LOGICAL SOCIETY. Complete to September 1890. Price IDS. (To Fellows, 5^.) INDEX TO THE PUBLICATIONS OF THE ENGLISH METEORO- LOGICAL SOCIETIES, 1839 to 1881. Price 2s. INDEX TO THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Vols. VIII. to XXVL, 1882- 1900. Price 2s. The above may be had at the Office of the Society, 70 VICTORIA STREET, LONDON, S.W. Printedby R. & R. Cl.ARK, LIMITED, Edinburgh. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. 24104