Difference between revisions 3102776 and 3318883 on mswiki

[[Fail:Longcase.jpg|right|thumb|Sebuah jam besar berdiri dengan sebuah jotak [[pain]], sekitar 1790, oleh Thomas Ross dari [[Kingston upon Hull|Hull]]. Dua lubang kunci pada kedua-dua belah dail menunjukkannya sebagai jam lapan hari.]]

Sebuah '''jam besar berdiri''', juga "jam peti panjang" atau "jam datuk", ialah sebuah [[jam batu ladung]] berdiri sendiri yang digerakkan oleh pemberat, dengan [[batu ladung]] digantung di dalam menara, atau pinggang peti [[jam (alat)|jam]]. Peti jenis ini umumnya sekitar 1.8-2.4m (6-8 kaki) tinggi. Peti ini sering dihias secara terperinci dengan ukiran pada hud, atau bonet, yang mengelilingi dan membingkai dail, atau [[muka jam]]. Pembuat jam Inggeris William Clement dikreditkan sebagai pengembang bentuk ini pada 1670. Kebanyakan jam besar berdiri merupakan [[jam berbunyi]], yang bermakna mereka membunyikan waktu pada setiap jam atau pecahan satu jam.

Istilah "jam datuk", "jam nenek", dan "jam cucu perempuan" telah digunakan untuk merujuk kepada jam besar berdiri. Walaupun tiada perbezaan khusus di kalangan istilah-istilah ini, pandangan umum menyatakan bahawa sebuah jam yang lebih kecil daripada 1.5 m (5 kaki) ialah jam cucu perempuan; 1.5m (5 kaki) ke atas ialah jam nenek; dan 1.8m (6 kaki) ke atas ialah jam datuk.

== Asal ==
{{BI|Longcase clock}}
[[Fail:Longcase clock movement.png|left|thumb|Cross section of a longcase clock movement without striking mechanism, mid-1800s.]]
The advent of the longcase clock is due to the invention of the [[anchor escapement]] mechanism around 1670. Prior to that, pendulum clock movements used an older [[verge escapement]] mechanism, which required very wide pendulum swings of about 100°.<ref name="Headrick">{{cite journal 
| last=Headrick 
| first=Michael 
| year=2002 
| title=Origin and Evolution of the Anchor Clock Escapement 
| journal=Control Systems magazine, 
| publisher=Inst. of Electrical and Electronic Engineers 
| volume=22 
| issue=2 
| url=http://www.geocities.com/mvhw/anchor.html 
| accessdate=2007-06-06|archiveurl=http://web.archive.org/20040914145830/www.geocities.com/mvhw/anchor.html|archivedate=2004-09-14}}</ref> Pendulum panjang dengan ayunan lebar semacam iyu tidak dapat dimuatkan dengan sebuah peti, jadi kebanyakan jam mempunyai pendulum pendek. Mekanisme anchor mengurangkan ayunan pendulum ke sekurangnya 4° to 6°,<ref name="Headrick" /> allowing clockmakers to use longer pendulums, which had slower "beats".  These needed less power to keep going, caused less friction and wear in the movement, and were more accurate.<ref name="Headrick" />  Most longcase clocks use a "seconds" (or "Royal"<ref>{{cite book
  | last =Nelthropp 
  | first = H. Leonard
  | authorlink = 
  | coauthors = 
  | title = A Treatise on Watch-Work, Past and Present
  | publisher = E.& F.N. Spon
  | date = 1873
  | location = London
  | pages = p.84
  | url = http://books.google.com/books?id=7DcDAAAAQAAJ&pg=PA84
  | doi = 
  | id = 
  | isbn = }}</ref>) pendulum, meaning that each swing takes one second.  These are about a metre (39 inches) long (to the centre of the bob).  This requirement for height, along with the need for a long drop space for the weights which power the clock,<ref>{{cite journal
  | last = Chappell
  | first = Jessica
  | authorlink = 
  | coauthors = 
  | title = The Long Case Clock: The science and engineering that goes into a grandfather clock
  | journal = Illumin
  | volume = 1
  | issue = 0
  | pages = p.4
  | publisher = Viterbi School of Engineering, USC
  | location = 
  | date = 2000
  | url = http://illumin.usc.edu/article.php?articleID=64&page=4
  | doi = 
  | id = 
  | accessdate = 2008-06-19}}</ref> gave rise to the design of the long narrow case.

Modern longcase clocks use a more accurate variation of the anchor escapement called the [[anchor escapement#deadbeat escapement|deadbeat escapement]].

== Penerangan ==
[[Fail:Grandfather clock q.jpg|right|thumb|Most of a longcase clock's height is used to hold the long [[pendulum]] and weights. The two chains attached to the weights and the lack of winding holes in the dial show this to be a 30-hour clock.]]
Traditionally, longcase clocks were made with two types of [[movement (clockwork)|movement]]: eight-day and one-day (30-hour) movements. A clock with an eight-day movement required winding only once a week, while generally less expensive 30-hour clocks had to be wound every day. Eight-day clocks are often driven by two weights - one driving the pendulum and the other the striking mechanism, which usually consisted of a bell or chimes. Such movements usually have two keyholes on either side of the dial to wind each one (as can be seen in the [[Thomas Ross (clockmaker)|Thomas Ross]] clock above). By contrast, 30-hour clocks often had a single weight to drive both the timekeeping and striking mechanisms. Some 30-hour clocks were made with false keyholes, for customers who wished that guests to their home would think that the household was able to afford the more expensive eight-day clock. All modern striking longcase clocks have eight-day movements. Most longcase clocks are cable-driven, meaning that the weights are suspended by cables.  If the cable was attached directly to the weight, the load would cause rotation and untwist the cable strands, so the cable wraps around a [[pulley]] mounted to the top of each weight.  The [[mechanical advantage]] of this arrangement also doubles the running time allowed by a given weight drop.  

Cable clocks are wound by inserting a special crank (called a "key") into holes in the clock's face and turning it.  Others, however, are chain-driven, meaning that the weights are suspended by chains that wrap around gears in the clock's mechanism, with the other end of the chain hanging down next to the weight.  To wind a chain-driven longcase clock, one pulls on the end of each chain, lifting the weights until the weights come up to just under the clock's face.

== Pengilang dahulu ==
'''Di England'''

*[[William Barrow (clockmaker)|William Barrow]], [[London]]
*[[Thomas Bullock (clockmaker)|Thomas Bullock]], [[Bath, Somerset|Bath]]
*[[Richard Donisthorp]] (fl. 1797), of [[Loughborough]]
*[[Peter Fearnley (clockmaker)|Peter Fearnley]], [[Wigan]]
*[[John Harrison]], [[Wakefield]]/[[Barrow-in-Furness|Barrow]]/[[London]]
*[[Edward Harrison]], [[Warrington]]
*[[William Lassell (clockmaker)|William Lassell]] (1758-1790), [[Toxteth]] Park, [[Liverpool]]
*[[Thomas Ross (clockmaker)|Thomas Ross]], [[Kingston-upon-Hull|Hull]]
*[[John Snelling (clockmaker)|John Snelling]], [[Alton, Hampshire|Alton]]
*[[Thomas Worswick (clockmaker)|Thomas Worswick]], [[Lancaster, Lancashire|Lancaster]]
*[[Henry Young (clockmaker)|Henry Young]], [[Swaffham]]
*[[Allam & Clements]]
*[[Thomas Cartwright (clockmaker)|Thomas Cartwright]]
*[[Matthew & Thomas Dutton]]
*Holmes
*[[Thomas Johnson (clockmaker)|Thomas Johnson]]
*[[Daniel Quare]]
*Trubshaw 
*[[Thomas Wright (clockmaker)|Thomas Wright]] 

'''Di Scotland'''
*[[Robert Bryson (clockmaker)|Robert Bryson]], [[Edinburgh]]
*[[James Howden (clockmaker)|James Howden]], [[Edinburgh]]
*[[Alexander Miller (clockmaker)|Alexander Miller]], [[Montrose, Angus|Montrose]]

'''Di Wales'''
*[[John Fernhill (clockmaker)|John Fernhill]], [[Wrexham]]
'''Clockmakers in the United States'''
*[[Luman Watson]] (1790-1834), [[Cincinnati]]
*[[Simon Willard]] (1753–1848), [[Roxbury, Massachusetts]]

== Pengilang kini ==
*[[Howard Miller Clock Company]]
*[[Seth Thomas Clock Company]]
*[[Ridgeway Clocks]]
*[[Bulova (syarikat)|Bulova Watch Company]]

== Pautan luar ==
*[http://www.charlesedwin.com/clkdiffs.htm Charles Edwin on the evaluation of antique clocks]
*[http://www.geoffreywalkerclocks.co.uk/Care%20of%20the%20longcase%20clock.shtml Care guide for valuable antique longcase clocks]
*[http://www.british-antiqueclocks.com/longcase-origins P A Oxley discuss the longcase clock]
*[http://www.british-antiqueclocks.com/longcase-installation P A Oxley-How to set up an antique longcase/grandfather clock]

== Nota kaki ==
{{reflist}}

[[Kategori:Jam]]
[[Kategori:Horologi]]