426 Description of Mr. South’s 
retain it there ; now address the other cone to the coarse 
screw ends of the bars, and by turning these in the direction 
of unscrewing, they will screw into their rings, and bring up 
the other cone to its bearing, with a power equal to the 
difference of the ranges of the two screws. The tubes of 
the telescope are united to the sphere and to each other in 
the same manner ; but to perform this operation, it is neces- 
sary to pass the hand into the sphere, for which purpose 
there are two apertures, with moveable caps left in the middle 
of its two uncovered parts : the tension bars are acted on by 
a capstan pin, small holes having been drilled in the bars to 
receive it. The above caps are covered with platina ; on 
one of them is engraved an inscription, and on the other the 
maker’s name. By the above mode of joining the principal 
parts, the bars may be stretched, and the sphere* even com- 
pressed to any extent short of that, which would occasion a 
permanent alteration in the length of the former, or in the 
figure of the latter ; a thing which Mr. Troughton con- 
siders would perhaps not take place with a force equal to a 
ton of weight. How much such a connection must be better 
than any that could be effected by binding together the 
exterior parts, to use the emphatic language of our illustrious 
artist, “ every one who is gifted with mechanical intellect 
will readily determine.” 
Plate XVIII. fig. 8, is a section through the axis, and ex- 
hibits the six bars which bind together, the cones of the axis, 
and also the places of the four, which are perpendicular to 
them, and which connect the tubes of the telescope. In 
Plate XVIII. fig. 9, which is a section through the telescope, 
* That every part of the sphere, should possess a power of resistance, as uniform 
as possible, extreme precaution was employed, in turning its interior surface, so as 
to render it concentric with the exterior. 
