B L I 



another man, not only of the order, diftanccs, and motions 

 of the heavenly bodies, but of the nature of light, and of 

 the laws of the reflection and refraftion of its rays. He 

 inay undcrftand diftinclly, how thofe laws produce the phe- 

 nomena of the rain-bow, the prifm, the camera obfcura, 

 and the magic lanthorn, and all tiie powers of the micro- 

 fcope and tthlcope, Neverthelefs, as to the appearances of 

 colour, a blind man mull be more at a lofs, becaufe he has no 

 perception tiiat rcfemSlts it ; though, by a kind ot analogy, 

 he may fupply even this defeft. 'i'o thofe who fee, a fcarlct 

 colour fignities an unknown quality in bodies, that exhibits 

 to the eye an appearance which they have often obferved, 

 and which they well kiiow ; but to a blind man, it denotes 

 an unknown quality that exhibits an appearance, with which 

 he is unacquainted. But he can conceive the eye to be va- 

 lioutly afieclcd by different colours, as the nofe is by differ- 

 ent fmells, or the ear by different founds : thus, he can 

 conceive fcarlet to differ from blue, as the found of a trum- 

 pet does from that of a drum ; or, as the fmell of an orange 

 diflers from that of an apple. It is impoffible to know whe- 

 ther fcarlet colour has the iame appearance to me which it has 

 to another man ; and if its appearances to diiferent perfons 

 differed as much as colour does from found, they might 

 never be able to difcover this difference. Hence it is plain, 

 that a blind man might talk for a long time about colours 

 dillindlly and pertinently ; and if you were to examine 

 him in the dark about the nature, compofition, and beauty 

 of them, he might be able to anfwer, io as not to betray 

 his defctt. After all, as a blind man has never had any 

 fenfatiou of light and colour, his knowledge concerning 

 them, however exteniive and accurate, mull be the refult of 

 previous inflruttion ; it muft depend on the force of genius, 

 or on the ftrength of memory ; and his language concerning 

 coloured objefts mull be like that of a parrot, without any 

 precifion of meaning, and without any correfpondlng ideas. 

 On this difputed fubjeft the reader may derive information 

 from Diderot's " Lettre fur les Aveugles a I'ufage de ceux 

 qui voyent," or " A Letter concerning the Blind for the 

 ufe of thofe who fee," in his " Works," vol. ii. ; and they 

 alfo may confult Chcfelden's " Anatomy," and Locke's 

 " Effay on the Human Underllanding." 



With regard to the fcientific and practical departments of 

 mufic, every age has fupplied numerous inllances of blind 

 perfons who have attaliied to great excellence. They will 

 occur among the articles of mulical biography in the courfe 

 of this work. 



Of the contrivances that have been devifed for the allift- 

 ance of the blind, we have already mentioned thofe of pro- 

 feffor Saunderfon, and of Mr. Grenville, under tlie article 

 Palpable Arithmetic. We fhall here fubjoin, from a 

 letter addreffed by Dr. Moyes to the editor of the " Ency- 

 clopcedia Britannica," an account of the palpable notation 

 generally ufed by him for twenty years, for the purpofe of 

 aflilling his memory in numerical computations. With this 

 view he made ufe of a fquare piece of mahogany, a foot 

 broad and an inch thick, reprefented by ABCD [Plate L 

 jllgebra, Jig.^.) ; he divided each of the fides AB, BC, 

 CD, DA, into 24 equal parts ; joined each pair of oppofite 

 divifions by a groove cut in the board of fufficient depth to 

 be felt with the finger ; and perforated the board at each in- 

 terfedtion with an inilrument -rV^h of an inch in diameter. 

 Having thus divided the furface of the board into 576 fmall 

 fquares, perforated at each of their angles, he fitted to the 

 holes in the board three fets of pegs or pins, refembling 

 thofe in the plate, Jigs. 4, 5, 6, in fuch a manner, that when 

 fixed in them they Kept their pofition, and required fonie force 

 to turn them round. The headof each peg belonging to the firft. 



B L I 



fet is a right-angled triangle, about ^Vli °^ =" '"cli chicle ; 

 the head of each peg beloriging to the fecond fet differs 

 from the former merely in havuig a Imall notch in its Hoping 

 fide or hypothenufe ; and the head of each peg of the third 

 fet is a fquare, the breadth of which Ihould be equal to the 

 bafe of the triangle of the other two. Thefe pegs Ihould 

 be kept in a cafe confilling of three boxes or cells, each 

 cell being allotted to a fet ; and the cafe muft be placed 

 clofe by the board before the connnencenient of every ope- 

 ration. Each fet Ihould confill of 60 or 70 pegs, at leaft 

 vi'hen employed in long calculations ; and when the work i^ 

 finilhed, they fliould be colleiled from the board, and care- 

 fully rellored to their refpedive boxes. Vv'hen a peg of the 

 firfl fet is fixed into the board, it will acquire four different 

 values, accordi-ng to its pofition with reiptft to the calcr- 

 lator. When; its floping fide is turned towards the left, it 

 denotes unit, or the firll digit ; when turned upwards, or 

 from the calculator, it denotes 2, or the fecond digit ; when 

 turned to the right, it reprefents 3 ; and when turned down- 

 wards, or towards the calculator, it denotes 4. The num- 

 ber 5 is denoted by a peg of the fecond iet, having its floping 

 fide turned to the left ; 6, by the tame turned upwards ; 7, 

 by the fame turned to the right ; and 8, by the lame turned 

 diredlly down, or towards the body of the calculator. The 

 figure 9 is expreffed by a peg of the third fort, when its 

 edges are diredled to right and left; and the fame peg expreffes 

 the cypher o, when its edges are direfted up and down. 

 By thefe different pegs the relative values of the ten digits 

 may therefore be dillinAly expreffed with facility ; and 

 by a fufficient number of each fet the fleps and relult of the 

 longeft calculation may be clearly reprefented to the fenfe 

 of feeling. For an example, let it be required to exprefs 

 the year of the Chrifli'an osra 1788. Take a peg of the 

 firfl fet, and fix it in the board, with its floping fide turned 

 towards the left, which reprefents I ; take a peg of the 

 fecond fet, and fix it in the next hole in the fame groove, 

 proceeding as ufual from left to right, with its floping fide 

 turned to the right, and this expreffes 7 ; take again a peg 

 of the fame fet, and fix it in the next hole, with its floping 

 fide turned downwards, and this will reprefent 8 ; and 

 laflly, take another peg of the fame fet, and place it in the 

 next hole in the fame pofition, which will denote S ; and 

 thus the whole will exprefs the number required. Li order 

 to exprefs a vulgar fraction, the numerator is placed in the 

 groove immediately above, and the denominator in that im- 

 mediately below the groove in which the integers fland ; 

 and in decimal arithmetic, an empty hole in the integer 

 groove reprefents the comma, or decimal point. By fimilar 

 breaks are alfo denoted pounds, ihiUings, pence, &c.; and 

 by the fame expedient, the divlfor and quotient in divifion 

 are feparated from the dividend. " This notation," fays 

 the ingenious inventor, " which fupplics me completely with 

 co-efficients and indices in algebra and fluxions, feems much 

 fuperior to any of the kind hitherto made public in the 

 well of Europe. That invented and defcribed by Mr. 

 Grenville, having no lefs than ten fets of pegs, is by 

 much too complicated for general praflice ; and that which 

 we owe to the celebrated Saunderfon, is apt to puzzle 

 and embanafs the calculator, as the pegs reprefenting th-e 

 numerical digits can feldora or never be in the fame 

 flraight line." 



It redounds very much to the honour of modern times, 

 that the public attention has been directed to the improve- 

 ment of the condition of blind perfons ; and that inititutions 

 have been formed in different countries for providing them 

 with fuitable employment, tending not only to alleviate their 

 calamity, but to render them ufttul. The firll regular ar.4 



fyllematic 



