A still further facility was given to the use of the filar micrometer by the introduction of clockwork, which caused the telescope automatically to follow the diurnal motion of a star, and left the observer's hands entirely at liberty.'
These lamps, although shown in the figure, are in reality covered so as not to shine upon the observer's eye.
2940, Dr Repsold proposed a method of meridian observing which consists in causing a web to follow the image of a star in transit by motions communicated by the observer's hands alone, whilst electrical contacts on the drum of the micrometer screw register on the chronograph the instants corresponding to known intervals from the line of collimation.
This has the effect of forming the image of the latter farther from the observer's eye, and so it becomes necessary to turn the handle of the rack-pinion V in such a way as to move the prisms P3 and P4 nearer to P2 till the lines of the stellar spectrograph are again sharply in focus.
A good deal perhaps depends on each observer's view of what religion really is.
For the first nine years of his reign his youth prevented him from taking more than an observer's part in affairs.
This wheel is acted on by a tangent screw whose bearings are attached to the cradle; the screw is turned by means of a handle supported by bearings attached to the cradle, and coming within convenient reach of the observer's hand.
Thus the scales, the positionand declination-circles, the field of view, the heads of all the micrometer-microscopes, the focusing scale, &c., are read without the aid of a hand-lamp and with an amount of illumination that can be regulated at the observer's pleasure.
(iv.) The state of adaptation of the observer's eye is dependent on his state of health, on a con dition of greater or less fatigue, or Circle of position ni ////fie on the inclina e,, ,,,y8222; head Circle tion of the (,?ccleofdedinataon: in consequence of, ?
It is due to the rotundity of the earth, and the height of the observer's eye above the water.
The dip of the horizon and its distance in sea-miles when the height of the observer's eye above the sea-level is h feet, are approximately given by the formulae: Dip=o' 97 -slh; Distance =1 m.
Continuous use of a periscope is very trying for the observer's eyes, and for use in bright weather light-filter screens are provided to reduce the glare.
Auroral Meridian.-It is a common belief that the summit of an auroral arc is to be looked for in the observer's magnetic meridian.
Thus there must in general be a difference between the observer's magnetic meridian - answering to the mean position of the magnetic needle at his station - and the direction the needle would have at a given hour, if undisturbed by the aurora, at any spot where the phenomena which the observer sees as aurora exist.
Under favourable conditions four concentric rings may be seen round the shadow of the observer's head, the outermost, which seldom appears, having an angular radius of 40°.
If we desire to, utilize all the parallel rays which fall upon an object-glass it is necessary that the full pencil of emerging rays should enter the observer's eye.
The hour circle has two toothed circles cut upon it, one acted upon by a worm screw mounted on the pier and driven by clockwork, the other by a second worm screw attached to the polar axis, which can be turned by a handle in the observer's hand and thus a slow movement can be given to the telescope in right ascension inde FIG.
The observer's eye is applied to the small telescope E, which (by means of prisms numbered I, 2, 3, 4) views the vernier attached to the cross-head simultaneously with the hour circle attached to the upper end of the polar axis.
The declination circle reads from the eye-end, and four handles for clamping and slow motion in right ascension and declination are situated near the observer's hands.
Other water engines, similarly connected, with keys at the observer's hands, rotate the dome and perform the quick motions in right ascension and declination.