« ElőzőTovább »
nearest to that indicated by the hygrometer) is 1211, which, divided by 484 1 (the temperature of the air increased by 448) gives 2.501 for the weight in grains of the moisture contained in a cubic foot of the atmosphere at the time and place of the observation. The logarithmic working of this example is given in the margin.
It only remains to notice the column headed "Radiation." The "solar radiation" is the excess of the indication of a thermometer with a blackened bulb when exposed to the direct rays of the sun, above that of a similar thermometer placed in the shade, the indications being observed simultaneously. The "terrestrial radiation" is the defect of the indication of a thermometer with a blackened bulb when exposed during the night upon a grass plat to the full aspect of the sky, below that of a similar thermometer placed under shelter.
It must be borne in mind that the results recorded at the head of the several months are the averages of observations made in by-gone years, with which it is extremely improbable that similar observations made in the corresponding month of any one subsequent year will entirely agree, but from which on the other hand it is improbable that the departure will be very considerable. Explanation of the columns headed" Length of day," "Day's increase or decrease,” Day breaks," and " Twilight ends."
THE column headed "Length of day" contains the number of hours and minutes
Equation of Time.
In the Almanacs of the Society the calculations are all made for mean time (given by the clock), instead of apparent time (given by the sun-dial), which latter had been used up to the year 1833. It must be obvious that, for all practical purposes, mean time is the most useful; and to obtain it from apparent time, the columns in the Almanac headed " Equation of Time" should be used. The column "Equation' of Time" ought, for example, to be consulted when persons are desirous of setting their clock by a sun-dial. When clock after sun is written above the number of minutes and seconds opposite to the day, then the clock ought to be set so much slower than the sun-dial, and the contrary.
THE Moon's age is set down in days and the nearest tenths of days from the time of
5th Pharmuti 2592
24th Cohiac 1560
2d Kaghots 1293 12th Kaghots
10th Dhulhajjah 1259
Poos or Margaly 4945
AUXILIARY TABLE FOR FINDING THE TIME OF SUNRISING AND SETTING.
The time of Sunrise and Sunset in the 'British Almanac' is adapted to the parallel of latitude in which London is situated-viz. 51° 30'.
THE following table has been constructed to show the variations of time through the United Kingdom-namely, between the latitude of 58° and 50° 10' N. The times of sun-rising and sun-setting are computed for the instant that the sun's centre is even with the horizon of the sea. The number of minutes found in this table under the month-day, and in the required latitude, are to be applied to the time of sun-rising and setting found on that day in the Almanac; the result will be the time of his rising and setting at the place required.-Ex. At what time will the sun rise and set on May 21 at Edinburgh? The time of sunrise and sunset on that day in the Almanac is 4h. 2m. A.M., and 7h. 52m. P.M. In the tables in parallel of 56°, in which Edinburgh is found, and under May 21, are 23 minutes; which, subtracted from 4h. 2m., leaves 3h. 39m. for time of sunrise; and, added to 7h 52m., gives 8h. 15m. for time of sun-setting.
The places which follow the different parallels are situate within 15 miles of latitude, either north or south of it.
58° 0'-Dornoch, Tain, Dunrobin, Portenleik, Dunclaim.
57° 30'-Peterhead, Fraserburg, Banff, Elgin, Cromarty, Inverness, Applecross.
57° 0'-Aberdeen, Bervie, Braemar, Laggan, Cornock.
56° 30'-Forfar, Dundee, Perth, Comrie, Ardchattan.
56° 0'-Berwick, Haddington, Edinburgh, Linlithgow, Kinross, Stirling, Dumbarton, Glasgow.
550 30-Embleton, Jedburgh, Selkirk, Sanquhar, Lanark, Irvine, Ayr.
550 0'-Newcastle, Morpeth, Carlisle, Annan, Dumfries, New Galloway, Wigtown. 54° 30'-Scarborough, Whitby, Hartlepool, Stockton, Richmond, Appleby, Cockermouth, Whitehaven, North part of Isle of Man.
54° 0'-New Malton, York, Aldborough, Clitheroe, Lancaster, Preston.
53° 30′-Grimsby, Kingston-upon-Hull, Pontefract, Manchester, Wigan, Liverpool, Beaumaris, Holyhead.
53° 0'-Lynn Regis, Boston, Lincoln, Nottingham, Derby, Stafford, Flint, Chester, Denbigh, Caernarvon, Harlech.
52° 30'-Yarmouth, Norwich, Thetford, Ely, Peterborough, Leicester, Coventry, Lichfield, Shrewsbury, Ludlow, Montgomery, Aberystwith.
52° 0'-Ipswich, Colchester, Cambridge, Hertford, Bedford, Buckingham, Oxford, Gloucester, Worcester, Hereford, Monmouth, Brecon, Caermarthen, Car digan, St. David's.
51° 30'-LONDON, Ramsgate, Canterbury, Rochester, Chelmsford, Windsor, Wallingford, Marlborough, Malmesbury, Bath, Bristol, Newport, Cardiff, Llandaff, Pembroke. 51° 0'-Dover, Winchelsea, Brighton, Guildford, Chichester, Winchester, Portsmouth, Southampton, Salisbury, Shaftesbury, Wells, Ilchester, Taunton, Bridgewater, Minehead, Barnstaple.
50° 30'-Newport (I. W.), Poole, Weymouth, Exeter, Ashburton, Totnes, Plymouth, Tavistock, Launceston, Bodmin, Camelford, Padstow.
50° 10′-Truro, Falmouth, Helstone, Penzance.
55° 0'-Carrickfergus, Antrim, Coleraine, Londonderry, Lifford, St. Johnstown. 54° 30'-Belfast, Killyleagh, Downpatrick, Armagh, Charlemont, Dungannon, Augher, Donegal. Ballyshannon, Enniskillen, Sligo.
54° 0'-Carlingford, Newry, Dundalk, Drogheda, Kells, Cavan, Belturbet, Carrick, Boyle, Castlebar, Killala.
53° 30′-Dublin, Swords, Naas, Athboy, Mullingar, Philipstown, Kilbeggan, Athlone,
Roscommon, Lanesboro', Tulsk, Tuam, Ballinrobe.
53° 0'-Wicklow, Blessington, Baltinglass, Carlow, Athy, Kildare, Portarlington, Maryboro', Ballynakill, Banagher, Galway, Ennis.
52° 30′-Newborough, Enniscorthy, Wexford, Kilkenny, Cullen, Clonmell, Cashell,
Killmallock, Limerick, Askeyton.
52° 0'-Waterford, Dungarvon, Youghal, Tallagh, Lismore, Rathcormack, Cork, Marlow, Killarney, Tralee, Ardfast, Dingle.
51° 30'-Kinsale, Bandor, Clonekelty, Baltimore.
The following List, showing the difference of Time between London and the Out-ports of the United Kingdom, as well as a few foreign Ports, is derived from Local Tide Tables, and the best books on Navigation.
To find the time of High Water at the above Places, it will be necessary to add or subtract the numbers in the above Table, according to the directions here given, to or from the time of High Water at London, as given in the Calendar for the day required.
For example:-On the 9th of January, the afternoon High Water at London Bridge is at 4h. 35m.; the High Water at Dover Harbour is 2h. 56m. earlier; subtract, according to the direction, 2h. 56m. from 4h. 35m., and the time of High Water at Dover Harbour on that day will be found to be at 1h. 39m. in the afternoon.