288 
HerscheWs Telescope » 
__ - ■ ' > 
To direct so immense a body to any part of the heavens 
at pleasure, much ingenuity, and many mechanical con 
trivances are evidently necessary. The whole apparatus 
rests upon rollers, and care was previously taken of the 
foundation in the ground. This consists of concentrical 
circular brick walls, the outermost 42 feet, the innermost 
21 in diameter ; 2 feet 6 inches deep under ground, 2 feet 
3 inches broad at the bottom, and 1 foot 2 inches at the 
top, capped with paving- stones, about 3 inches thick, 
and 12 3-4 inches broad. In the centre is a large post of 
oak, framed together with braces under ground, and wall- 
ed fast with brick- work, to make it steady. Round this 
centre, the whole frame is moved horizontally, by means 
of 20 rollers, 12 upon the outer and 8 upon the inner 
wall. 
The vertical motion is given to the telescope by means 
of ropes and pullies, as seen in the plate, passing over the 
main-beam, supported by the ladders. These ladders are 
in length forty-nine feet two inches ; and there is a movea - 
ble gallery with twenty-four rollers to ease its motion* 
The small stair-case visible in the plate, is intended for 
persons who wish to ascend into the gallery, without being 
obliged to go up the ladder. The ease with which the 
horizontal and vertical motions may be communicated to 
the tube will be best conceived from a remark of Her- 
schell, that, in the year 1789, he several times observed 
Saturn two or three hours before and after its meridian 
passage, with one single person to continue at his directions 
the necessary horizontal and vertical motions. 
Upon the platform are visible two rooms, the one called 
the Observatory, eight feet five inches, by five feet five 
inches, the other called the Working-room six feet six 
inches by four feet five inches. To persons in these 
rooms, as has been above remarked, the observer can give 
his directions by means of the speaking- pipes ; and in 
- - - 
