*14 B L I 
which might be oceafioned by its lefs formidable inequali¬ 
ties, but, from its general bias, he collects Come ideas how 
iar his fafecy is immediately concerned; and, though thefe 
conjectures may be fometimes fallacious, yet they are ge¬ 
nerally fo true, as to preferve him from fuch accidents as 
are not incurred by his own temerity. The rapid torrent, 
and the deep cafcade, not only warn him to keep a proper 
dittance, but inform hint in what direction he moves, and 
are a kind of audible fynofures to regulate his courfe. In 
places to;which he has been accudomed, he as it were re- 
cognifes his latitude and longitude from every breath of 
varied fragrance that tinges the gale, from every afcent 
or declivity in the road, from every natural or artificial 
found that ftrikes his ear • if thefe indications be dation- 
ary, and confined to particular places. Regulated by thefe 
figns, the blind have not only been known to perform long 
journeys themfelves, but to conduct others through dan¬ 
gerous paths at the dark and filent hour of midnight, with 
• the utinod fecluity and exadnefs. We are told by Ca- 
iaubon and Leo Africanus, of a very extraordinary blind 
guide, who uled to conduct the merchants through the 
lands and deferts of Arabia ; and in our own country we 
have a very remarkable indance of a blind guide in John 
Metcalf, of Mancheder, who very lately followed the oc¬ 
cupation of conducting dt angers through intricate roads 
during the night, or when the tracks were covered with 
ih'ow. And, drange as this may appear to thofe who can 
fee, the employment of this man was afterwards that of a 
projector and furveyor of highways in difficult and moun¬ 
tainous parts. With the abidance only of a long baft’, he 
has been feveral times leen traverfing tire roads, afcending 
-precipice's, exploring valleys, and invedigating their fe¬ 
veral extents, forms, and Situations, fo as to anlwer his 
defigns in the bed manner. Mod of the roads over the 
Peak'in Derbyfhire have been altered by his directions ; 
particularly thofe in the vicinity of Buxton : and he has 
fince condruded a new one betwixt Wilmdovv and Con- 
gleton, with a view to open a communication to the great 
London road, without being obliged to pafs over tlie 
mountains. See the account by Dr. Bew, publilhed in 
the TranfaCtions of the Mancheder Society. 
It were endlefs to mention the various mechanical ope¬ 
rations of which the blind are capable, by their nicety and 
accuracy of touch. In fome, the taCtile powers are laid 
to have been fo highly improved, as to perceive that tex¬ 
ture and difpodtion of coloured furfaces by which fome 
rays of light are reflected and others abforbed, and in this 
manner to didinguidi colours. The tedimonies, however, 
for this faCt, appear too vague and general to deferve pub¬ 
lic credit. But that their acoudic perceptions are didinCt 
and accurate, we may fairly conclude from the rapidity 
with which they afcertain the acutenefs or gravity of dif¬ 
ferent tones, as relative one to another; and from their ex- 
aCt difcernment of the various kinds and modifications of 
found, and of fonorous objeds, if the founds themfelves 
be in any degree fignificant of their caufes. From this 
accuracy of external fenfation, and from the abiduous ap¬ 
plications of a comprehenfive and attentive mind, we are 
able to account for the rapid and adonidiing progrefs 
which fome of them have made in thofe departments of 
literature, which were mod obvious to their denies and 
acceffible to their underdandings. What, for indance, 
can be more remote from the conceptions of a blind man 
than the abdrad relations and properties of Ipace and 
quantity ? yet the incomprehenfible attainments of doctor 
Saunderfon, of Cambridge, in all the branches of mathe¬ 
matics, are now fully known by the literary world, both 
from the tedimony of his pupils, and the publication of 
his works. But, fhould the fail be ftill uncertain, it might 
-Te diffidently verified by a living indance, in the peribn of 
d oft or Moyes, of Mancheder, who, though blind from his 
Infancy, by the ardour and alTiduity of his application, and 
by the force of natural genius, has not only made great ad¬ 
vances in mechanical operations, in mufic, and in the lan¬ 
guages ; but is like wife (killed in geometry, in .optics, in 
N D. 
algebra, in adror.omy, in chemidry, and in mod other 
branches of natural philofophy. His example alone is 
abundantly diffident to do away the vulgar prejudice, 
which predimes to think blindnefs and learning incom¬ 
patible ; and that the cultivation of the talents of blind 
perfons is a weary and unpromifing talk. 
Many attempts have been made to invedigate, both 
from reafon a priori, and from experiment, what might be 
the primary effects of light and luminous objects upon fuch 
as have been born blind, or early deprived of fight, if at 
a maturer period they diould inftantaneoufly recover their 
vilual powers. But upon this topic there is much reafon 
to fear, that nothing fatisfadory has yet been difcovcred. 
The fallacy of hypothefis and conjecture, when formed 
a priori with refped to any organ of corporeal fenfation 
and its proper object, is too obvious to demand illudra- 
tion. But from the nature of the eye, and the mediums 
of its perception, to attempt an inveltigation of the various 
and multiform phenomena of vifion, would be a mod ro¬ 
mantic undertaking. Even the difcoveries which are faid 
to accrue from experiment, may be held as extremely 
doubtful and precarious; becaufe in thefe experiments it 
does not appear to have been afcertained, that the organs 
to which vilible objeds were prel’ented immediately after 
chinirgical operations, could be in a proper date to per¬ 
ceive them. Yet, after all, it is extremely probable, that 
figure, didance, and magnitude, are not immediate objeds 
of ocular fenfation, but acquired and adjuded by long and 
reiterated experience. The gentleniart Couched by Mr. 
Chefelden had no idea of didance; but thought that all 
the objeds he law touched his eyes, as what he felt did 
lii.s (kin. It was alfo a conliderable time before he could 
remember which was the cat, and which the dog, without 
feeling them. There are many dedderata, which the per¬ 
ceptions of a man born blind might confiderabiy illuf- 
trate, if his indruments of vifion were in a right date, and 
affided by a proper medium. Such a perfon might per¬ 
haps give a clearer account, why objeds, whofe pidures 
are inverted upon the retina of the eye, diould appear to 
the mind in their real pofitions ; or why, though each 
particular objed is painted upon the retina of both our 
eyes, it fhould only be perceived as fingle. Perhaps, too, 
this new l'pedator of vilible nature might equally amufe 
our curiofity and improve our theory, by attempting to 
defcnbe his earlied fenfations of colour, and its original 
ededs upon his organ and his fancy. It is far from being 
certain, however, that trials of this kind have ever been 
fairly made. For a more minute detail of thefe points the 
reader may confult M. Diderot’s Lettre lur les Aveugles, 
a. Pillage de ceux qui voyent; alfo Mr. Chefelden’s Ana¬ 
tomy, and Locke’s Effay on the Human Underdanding. 
When we refled on the numberlefs advantages derived 
from the ufe of light, and its immenfe importance in ex¬ 
tending the human capacity, we might be tempted to 
doubt the fidelity of thofe reports concerning fuch perfons 
as, without the affidance of light, have arrived at high 
degrees of eminence even in thofe fciences which appear 
abfohitely unattainable but by the interpofition of external 
mediums. It has, however, been deinondrated by Dr. 
Reid, in his Inquiry into the Human Mind, that blind 
men, by proper indrudions, are fulceptible almod of 
every idea and of every truth which can be imprelfed on 
the mind by the mediation of light and colours, except 
the fenfations of light and colours themfelves. Yet there 
is one phenomenon of this kind which feems to have ef- 
caped the attention of that great philofopher, and of which 
no author has hitherto been able to offer any tolerable fo- 
lution. Although we diould admit, that the blind can 
underdand with great perfpicacity all the phenomena of 
light and colours ; though it were allowed, that in thefe 
fubjeds they might extend their fpeculations beyond their 
indrudions, and invedigate the mechanical principles of 
optics by the mere force of genius and application, from 
the data which they had already obtained ; yet it will be 
difficult, if not impoffible, to affign any reafon why thefe 
objeds 
