14 MEASUREMENT OF MAN’S INFLUENCE. 
pose to take of it, is yet in that imperfectly developed state 
which allows its votaries to occupy themselves with broad and 
general views attainable by every person of culture, and it does 
not now require a knowledge of special details which only years 
of application can master. It may be profitably pursued by 
all; and every traveller, every lover of rural scenery, every agri- 
culturist, who will wisely use the gift of sight, may add valuable 
contributions to the common stock of knowledge on a subject 
which, as I hope to convince my readers, though long neglected, 
and now inartificially presented, is not only a very important 
but a very interesting field of inquiry. 
Measurement of Man's Influence. 
The exact measurement of the geographical and climatic 
changes hitherto effected by man is impracticable, and we pos- 
sess, in relation to them, the means of only qualitative, not 
quantitative analysis. The fact of such revolutions is established 
deaf-and-dumb schools, and others where pupils are first taught to write on 
large slates or blackboards. The writing is in large characters, the small 
letters being an inch or more high. They are formed with chalk or a slate 
pencil firmly grasped in the fingers, and by appropriate motions of the wrist, 
elbow, and shoulder, not of the finger joints. Nevertheless, when a pen is 
put into the hand of a pupil thus taught, his handwriting, though produced 
by a totally different set of muscles and muscular movements, is identical in 
character with that which he has practised on the blackboard. 
For a very remarkable account of the restoration of vision impaired from 
age, by judicious training, see Lessons in Life, by TrmoTHy TITCOMB, les- 
son xi, 
It has been much doubted whether the artists of the classic ages possessed 
amore perfect sight than those of modern times, or whether, in executing 
their minute mosaics and gem engravings, they used magnifiers. Glasses 
ground convex have been found at Pompeii, but they are too rudely fashioned 
and too imperfectly polished to have been of any practical use for optical pur- 
poses. But though the ancient artists may have had a microscopic vision, 
their astronomers cannot have had a telescopic power of sight; for they did 
not discover the satellites of Jupiter, which are often seen with the naked eye 
at Oormeeah, in Persia, and sometimes, as I can testify by personal observa- 
tion, at Cairo. 
