張思訓,今四川巴(ba)(ba)中(zhong)(zhong)(巴(ba)(ba)州區)石城(cheng)人(ren)(ren)(ren),北宋時(shi)期的(de)(de)著名天(tian)(tian)文學(xue)家(jia),曾是(shi)(shi)司(si)天(tian)(tian)展(zhan)覽館監(jian)學(xue)生。公元979年對(dui)渾(hun)(hun)(hun)天(tian)(tian)儀(yi)(yi)進(jin)行(xing)了(le)重大(da)的(de)(de)革(ge)新,制(zhi)造了(le)世界上第一臺自(zi)(zi)(zi)動天(tian)(tian)象儀(yi)(yi)——太平渾(hun)(hun)(hun)儀(yi)(yi),又(you)稱(cheng)水(shui)(shui)(shui)(shui)運(yun)渾(hun)(hun)(hun)象。此(ci)儀(yi)(yi)用(yong)水(shui)(shui)(shui)(shui)銀(yin)作動力,是(shi)(shi)世界上使用(yong)水(shui)(shui)(shui)(shui)銀(yin)于機(ji)械(xie)儀(yi)(yi)表(biao)的(de)(de)始祖。自(zi)(zi)(zi)落下閎創造渾(hun)(hun)(hun)天(tian)(tian)儀(yi)(yi)之后,最(zui)(zui)初用(yong)人(ren)(ren)(ren)力推動其(qi)運(yun)轉(zhuan)(zhuan),后來改(gai)用(yong)水(shui)(shui)(shui)(shui)力。但是(shi)(shi)人(ren)(ren)(ren)們在實(shi)踐中(zhong)(zhong)發現(xian),“運(yun)轉(zhuan)(zhuan)以(yi)水(shui)(shui)(shui)(shui),至冬中(zhong)(zhong)凝凍(dong)遲(chi)澀,遂(sui)為(wei)(wei)疏略,寒暑無準”。這(zhe)(zhe)樣對(dui)于報時(shi)、定(ding)節氣、造歷的(de)(de)準確性關系(xi)極大(da),進(jin)而影響到(dao)人(ren)(ren)(ren)民的(de)(de)生產(chan)和生活。面(mian)對(dui)渾(hun)(hun)(hun)天(tian)(tian)儀(yi)(yi)動力出(chu)現(xian)的(de)(de)新課題,張思訓進(jin)行(xing)了(le)許多試驗和探(tan)索,最(zui)(zui)終(zhong)找到(dao)用(yong)水(shui)(shui)(shui)(shui)銀(yin)代替水(shui)(shui)(shui)(shui)作動力。因為(wei)(wei)水(shui)(shui)(shui)(shui)銀(yin)的(de)(de)內聚力很強,特別是(shi)(shi)具有在空中(zhong)(zhong)保持穩定(ding)的(de)(de)性能,可保證渾(hun)(hun)(hun)天(tian)(tian)儀(yi)(yi)正常的(de)(de)運(yun)轉(zhuan)(zhuan)。在渾(hun)(hun)(hun)天(tian)(tian)儀(yi)(yi)上安(an)裝計時(shi)器,是(shi)(shi)我國唐代天(tian)(tian)文學(xue)家(jia)一行(xing)、梁令瓚的(de)(de)發明(ming)。他們在水(shui)(shui)(shui)(shui)運(yun)渾(hun)(hun)(hun)天(tian)(tian)儀(yi)(yi)上安(an)裝擒縱(zong)器,指揮(hui)兩(liang)(liang)個(ge)木人(ren)(ren)(ren)按時(shi)擊(ji)(ji)鼓(gu)、敲鐘(zhong)(zhong)(zhong),產(chan)生了(le)世界上最(zui)(zui)早(zao)的(de)(de)機(ji)械(xie)時(shi)鐘(zhong)(zhong)(zhong)。張思訓對(dui)這(zhe)(zhe)個(ge)機(ji)械(xie)計時(shi)鐘(zhong)(zhong)(zhong)也進(jin)行(xing)了(le)較(jiao)大(da)改(gai)革(ge)。由擒縱(zong)器指揮(hui)的(de)(de)自(zi)(zi)(zi)動報時(shi)和擊(ji)(ji)鐘(zhong)(zhong)(zhong)鼓(gu)的(de)(de)木人(ren)(ren)(ren)成(cheng)倍增加(jia),并把報時(shi)和擊(ji)(ji)鐘(zhong)(zhong)(zhong)鼓(gu)分離為(wei)(wei)兩(liang)(liang)個(ge)系(xi)統,即“七值(zhi)神左(zuo)搖鈴,右(you)扣鐘(zhong)(zhong)(zhong),中(zhong)(zhong)擊(ji)(ji)鼓(gu),以(yi)定(ding)刻數。每(mei)一晝(zhou)夜(ye),周而復始。又(you)為(wei)(wei)十二神各值(zhi)一時(shi)。至其(qi)時(shi),則自(zi)(zi)(zi)執辰牌,循(xun)環而出(chu),隨刻數以(yi)定(ding)晝(zhou)夜(ye)短長”。《宋史·天(tian)(tian)文志》稱(cheng):“其(qi)制(zhi)與舊儀(yi)(yi)不同,最(zui)(zui)為(wei)(wei)巧捷”。袁綱《楓(feng)窗小牘》贊:“新制(zhi)成(cheng)于自(zi)(zi)(zi)然,尤為(wei)(wei)精(jing)妙”。
張思訓於公(gong)元(yuan)979年設計(ji)的渾象,於公(gong)元(yuan)980年制成。據《宋史(shi)?天(tian)(tian)(tian)(tian)(tian)文志(zhi)》載(zai):「其(qi)制:起樓(lou)高丈馀,機(ji)隱於內,規(gui)天(tian)(tian)(tian)(tian)(tian)矩(ju)地(di)。下設地(di)輪(lun)、地(di)足;又為橫(heng)輪(lun)、側輪(lun)、斜輪(lun)、定(ding)身關、中關、小(xiao)關、天(tian)(tian)(tian)(tian)(tian)柱;七直神,左搖鈴,右扣鐘,中擊鼓(gu),以(yi)定(ding)刻(ke)數(shu)。每一晝(zhou)夜,周而復始。又以(yi)木為十(shi)二(er)神,各直一時(shi),至(zhi)其(qi)時(shi)則自執辰牌(pai),循環而出(chu),隨刻(ke)數(shu)以(yi)定(ding)晝(zhou)夜短長;上有(you)天(tian)(tian)(tian)(tian)(tian)頂、天(tian)(tian)(tian)(tian)(tian)牙、天(tian)(tian)(tian)(tian)(tian)關、天(tian)(tian)(tian)(tian)(tian)指、天(tian)(tian)(tian)(tian)(tian)抱(托(tuo))、天(tian)(tian)(tian)(tian)(tian)束、天(tian)(tian)(tian)(tian)(tian)條,布三(san)百六十(shi)五度,為日(ri)、月、五星、紫(zi)微(wei)宮、列宿、斗建、黃(huang)赤道(dao),以(yi)日(ri)行度定(ding)寒(han)暑進退。」
這段文字所記載(zai)的(de)機(ji)械部件和(he)齒輪名稱(cheng),比唐代一行和(he)梁(liang)令瓚的(de)「水運渾天(tian)(tian)」記載(zai)要詳細得(de)多(duo)。其中(zhong)的(de)「地輪」可能和(he)蘇頌水運儀象臺的(de)「樞輪」即動(dong)(dong)(dong)力輪相(xiang)類(lei)似。「定(ding)身關、中(zhong)關、小關」一類(lei)機(ji)械也可能與蘇頌的(de)天(tian)(tian)關、天(tian)(tian)鎖的(de)功(gong)效雷同,是用(yong)於控(kong)制「地輪」的(de)慣性運動(dong)(dong)(dong)的(de),也就(jiu)是起(qi)擒縱器(qi)的(de)作用(yong)。「定(ding)身關」一詞(ci)生動(dong)(dong)(dong)地表述了(le)控(kong)制「地輪」轉動(dong)(dong)(dong)的(de)意(yi)義(yi)。而在(zai)報時(shi)機(ji)械之上的(de)「天(tian)(tian)牙」、「天(tian)(tian)關」、「天(tian)(tian)束(shu)」、「天(tian)(tian)條」等機(ji)件又(you)可能是操縱渾儀或渾象的(de)設置。以木(mu)偶制成的(de)「七直神」、「十(shi)二神」是報時(shi)機(ji)件。
張思訓的(de)這架天(tian)(tian)文鐘與一行(xing)(xing)不同之處,是以水(shui)銀推動(dong)動(dong)力輪,同時,「著日(ri)月(yue)象,皆取仰視」。《宋史?天(tian)(tian)文志》還說:「按舊法(fa),日(ri)月(yue)晝夜行(xing)(xing)度皆人所運行(xing)(xing),新制成於(wu)自(zi)然,尤為精妙。」看來,張衡和一行(xing)(xing)等人的(de)渾象都有(you)部分(fen)需人操作或調(diao)整(zheng),而張思訓則設計了一種全自(zi)動(dong)的(de)渾象。
可惜,有關張思訓儀象的(de)文(wen)字記載過於簡略,更無繪圖(tu)留下來供(gong)我們研究。因而(er)蘇頌的(de)《新儀象法要》,在人類文(wen)化史(shi)上(shang)就顯(xian)得更為可貴了。