■VVONCEES OF ART. 
leflected. by a minor, as in the Gregorian telescope, 
the ia_ys are intcrceptod l)y a lens at a proper distance, ^ 
that the observer has his back to the object, and look* 
through the lens at the mirror. The magnifying power '* 
the same as in the Newtonian telescope ; hut there not beinJ 
any ^cond reflector, the brightness of the object viewed >" 
the Herschel telescope is greater than that in the Newtonian ' 
telescope. , 
The tube of Doctor Herschel’s grand telescope '* 
39 feet 4 inches in length, and 4 feet 10 inches in diameteb, 
e\ ery part being made of iron. The concave polished surface^’* 
tne great mirror is 4 feet in diameter, its thickness 3 \ inche*' 
and Its weight upwards of 2000lbs. This noble instrumen', 
was, m ^1 its parts, constructed under the sole direction 
Doctor Herschel : it was begun in the year 1785, and coih' 
]4cted August 2Sth 1 789, on which day was discovered t)i» 
sixth sateliite of Saturn. It magnifies six thousand 
TIMES. 
Illustration of the cut. A B C is a rav of light, reflect®*^ 
by the great speculum B to the eye-glasL C D is a cha>'' 
for the observer. E, a moVeable gallery for spectator*- 
f G, a smooth base for the frame to turn on. H and I> 
puJlies to move the instrument. K are rooms for assistants- 
THE ENGLISH TELEGRAPH. 
Between London and Portsmouth there are twelve station*' 
and thirty-one between London and Plymouth, of whid‘ 
eight are part of the Portsmoutli line till tliey separate in th® 
New Forest. Another chain, extending from London t<* 
lainiouth, contains nineteen stations j and another 
London to Deal, ten stations ; making in the whole systE*** 
si.tty-four telegraphs. The distances average about 
mile.s, yet some of them e.xtend to twelve or fourteen j tin 
the lines are often increased by circuits, for want of coin' 
manding heights. In the Yarmouth line particularly, tl>‘' 
chain makes a considerable detour to the northward. 
After about twenty years’ experience, they calculate ^ 
about two hundred days on which signals can be transinilten 
throughout the day j about sixty others on which they 
pass only part of the day, or at particular stations ■, n® 
about one Hundred days "in which few of the stations ^ 
