U N I 



UNI 



thants. — Alfo, a townfliip of Highland county, Ohio, 

 containing 744 inhabitants. — Alfo, a townfhip in Knox 

 county, Ohio, containing 431 inliabitants — Alfo, a town- 

 fhip in Licking county, Ohio, containing 375 inhabitants. 

 • — Alfo, a townfhip in Madifon county, Ohio, containing 

 ZCO inliabitants. — Alfo, a townfhip in Miam county, Ohio, 

 containing 683 inhabitants. — Alfo, a townfliip in Muf- 

 kingum county, containing 430 inhabitants Alfo, a town- 

 fhip in Rofs county, Ohio, containing 2273 inhabitants. — 

 Alfo, a townfhip in Scioto county, Ohio, containing 541 

 .inhabitants. — Alfo, a diflrift of South Carolina, containing 

 10,995 inhabitants. 



Union Borough, a town in Fayette county, Pennfylvania, 

 containing 999 inhabitants. 



Union River, a river of the diftritl of Maine, which 

 runs into Penoblcot bay. 



Union Springs, a poft-office in the fouth-weft corner of 

 Aurelius, in Cayuga county. 



Union Fire-Office, See Insurance. 

 UNIONS, Uniones, in Phyftology, the fame with mar- 

 garita, or pearls. See Pearl. 



UNIQUE is fometimes anglified, and ufed to denote a 

 thing which is the only one of its kind. 



UNISETA, in Natural Hiftory, the name of a fpecies 

 of fly, found frequently fitting on the ammi or bilhops 

 weed, and diflinguifhed by having one long hair or briflle 

 growing out at its tail. See Henothrix. 



UNISON, in Mufic, is the efFeft of two founds, which 

 are equal, in degree of tune, or in point of gravity and 

 acutenefs. 



Unifon may be defined a confonance of two founds, pro- 

 duced by two firings, or other bodies of the fame matter, 

 length, thicknefs, and tenfion, equally ftruck and at the 

 fame time ; fo that they yield the lame tone or note. 



Or it is the union of two founds, fo like each other, that 

 ■the ear, perceiving no difference, receives them as one and 

 the fame found. See Sound. 



What conftitutes unifonance is the equality of the number 

 of vibrations of the two fonorous bodies in equal times ; 

 where there is an inequality in that refpeft, and, of confe- 

 quence, an inequality in degree of tune, the unequal founds 

 conftitute an interval. 



Since ifochronous vibrations produce founds that are 

 mufical, and that are faid to continue at the fame pitch, and 

 flower vibrations produce graver, flatter, or lower founds, 

 and quicker vibrations produce founds that are acuter, 

 fharper, or higher ; it follows, that if fcvcral firings, how- 

 ever different in length, thicknefs, denlity, and tenfion, or 

 other founding bodies, vibrate all together in equal times, 

 their founds will liave one and the fame pitch, however they 

 may differ in loudnefs, or other qualities, and are, therefore, 

 called unifons ; and, on the contrary, the vibrations of 

 unifons arc ifochronous. This obfervation reduces the 

 theory of all forts of mufical founds to that of the founds of 

 a fingle firing, with refpeft to gravity or acutenefs. Con- 

 fequeiitly, the wider and narrower vibrations of a mufical 

 firing, or of any other body founding mufically, are all 

 ifochronous very nearly : otherwifc, while the vibrations 

 decreafe in breadth till they eeafe, the pitch of the found 

 could not continue the fame as we perceive it does, if the 

 firft vibrations be not too large ; in which cafe, the found 

 is a little acuter at the beginning than afterwards. In like 

 manner, fince the pitch of the found of a firing or bell, or 

 other vibrating body, does not fenfibly alter, while the 

 hearer varies his diilance from it ; it follows, that the larger 

 and leffer vibrations of the particles of air, at fmaller and 

 greater dillances from the founding body, are all. ifo- 

 chronous ; and confcquently, that the little fpaccs defcribed 

 Vol. XXXVII. 



by the vibratuig particles are every where proportional to 

 the celerity and force of their motions, as in a pendulum ; 

 and this difference of force, at different dillances from the 

 founding body, caufes a difference in the loudnefs of the 

 found, but not in its pitch. It follows alfo, that the har- 

 mony of two or more founds, according as it is perfeA or 

 imperfeft at any one diftancc, will alfo be perfeft or im- 

 perfcft at any other diftance ; and this is a known faft, 

 «. gr. in a ring of bells. If two mufical firings (fee String) 

 have the fame thicknefs, denfity, and tenfion, and differ in 

 length only, mathematicians have demonltrated, that the 

 times of their fingle vibrations are proportional to their 

 lengths. Hence, if a firing of a mufical inflrument be 

 flopped in the middle, and the found of the half be com- 

 pared with that of the whole, we may acquire the idea of 

 the interval of two founds, whofe fingle vibrations («'. e. the 

 times) are in the ratio of i to 2 ; and by comparing the 

 founds of -5, 4, f, \, |., 4, ,°„, &c. of the firing with the 

 found of the whole, we may acquire the ideas of the in- 

 tervals of two founds, whofe fingle vibrations are in the 

 ratio of 2 to 3, 3 to 4, 3 to 5, 4 to 5, 5 to 6, 8 to 9, and 

 9 to 10, &c. See Chord. .Smith's Harmonics, p. 2, &c. 



Unifon is the firft and greatefl of concords, and the 

 foundation, or, as fome call it, the mother of all the reft ; 

 yet others deny it to be any concord at all, maintaining it to 

 be only that in founds, which unity is in numbers. 



Thefc reftrain the word concord to intervals, and make it 

 include a difference of tune : but this is precarious ; for as 

 the word concord fignifies an agreement of founds, it is cer- 

 tainly applicable to unifons in the fiill degree. 



But though unifonance, or an equality of tune, makes the 

 moft perfeft agreement of found, it is not true that the 

 nearer any two founds come to an equality of tune, they 

 are the more agreeable. The mind is delighted with va- 

 riety ; and the reafon of the agreeablenefs or difagreeablenefs 

 of two founds muft be afcribed to fome other ciufe than the 

 equality or inequality of the number of their vibrations. 



It is a famed phenomenon in mufic, that an intenfe found 

 being railed, either with the voice, or a fonorous body, 

 another fonorous body near it, whofe tune is either unifon, 

 or oftave to that found, will found its proper note unifon, 

 or oftave, to the given note. 



The experiment is eafily tried by the firings of two in- 

 flrume nts ; or by a voice and an harpfichord ; or a bell, or 

 even a drinking-glafs. 



This our philofopliers account for thus : one ftring being 

 ftruck, and the air put in motion thereby ; every other 

 ftring, within the reach of that motion, will receive fome 

 impreflion therefrom : but each ftring can only move with a 

 determinate velocity of recourfes or vibrations ; and all uni- 

 fons proceed from equal, or equidiurnal vibrations ; and 

 other concords from other proportions. The unifon ftring, 

 then, keeping equal pace with the founded ftring, as having 

 the fame mcafure of vibrations, mull have its motion con- 

 tinued, and Itill improved, till its motion become fenfible, 

 and it give a tlidinft found. Other concording ftrings have 

 their motions propagated in different degives, according to 

 the frequency of the coincidence of their vibr.it ions with 

 thofe of the founded ftring : the oftave, therefore, moft 

 fenfibly ; then the fifth ; after which, the crofTing of the 

 motions prevents any cffeCt. 



This they illullrate (as Galileo firft fuggeftcd) by the 

 pendulum, which being fet a moving, the motion may be 

 continued and augmented, by making frequent, light, coin- 

 cident impulfcs ; as blowing on it when the vibration is juft 

 finifhed : but if it be touchid by .my crofs or oppofite mo- 

 tion, and this, too, frequently, the motion will be inter- 

 rupted, and ceafe altogether. So of two unifon ftrings, if 

 3E the 



