Two new Micrometers, 431 
and, if the frame is moved towards the right, the relative 
motion of the two frames is (hewn on the fcale l by the 
vernier m ; but if the frame b be moved towards the left, 
the relative motion is fhewn by the vernier n. 
This micrometer has a motion round the axis of vi- 
lion, for the conveniency of meafuring the diameter of a 
planet, 8ec. in any direction, by turning an endlefs fcrew 
F, and the inclination of the diameter meafured with the 
horizon is fhewn on the circle g by a vernier on the 
plate v. The telefcope may be adjufted to diftinct vifion 
by means of an adjufting fcrew, which moves the whole 
eye tube with the micrometer nearer or farther from the 
object glafs, as telefcopes are generally made; or the fame 
effect may be produced in a better manner, without 
moving the micrometer, by Hiding the part of the eye 
tube m on the part n, by help of a fcrew or pinion. The 
micrometer is made to take off occafionally from the eye 
tube, that the telefcope may be ufed without it. 
Lila 
