To all these causes must be added - not least important in dealing with orientals - the widespread feeling since the Afghan disaster that the star of the company was in the descendant, and that there was truth in the old prophecy that the British would rule in India for a bare century from Plassey (1757).
Under these conditions there is no doubt that the star would appear to be fairly resolved, since the brightness of its external ring system is too small to produce any material confusion, unless indeed the components are of very unequal magnitude.
In both cases no extraneous cause can be assigned; the period seems to be inherent in the star itself and not to be determined by the revolution of a satellite (no variability of the line-of-sight motion of Mira has been found, so that it is probably not accompanied by any large companion).
Their detection is especially simple when the stereo-comparator is used; this instrument enables the two eyes to combine the images of each star on two plates into one image (as in the stereoscope); when the star has moved considerably in the interval between the taking of the two plates, it appears to stand out from the rest in relief and is at once noticed.
The people at once followed and formed a circle around the sides of the spacious room, leaving the horse and buggy and the man with the star to occupy the center of the hall.
When the earth is at A, in consequence of aberration, the star is displaced to a point a, its displacement sa being parallel to the earth's motion at A; when the earth is at B, the star appears at b; and so on throughout an orbital revolution of the earth.
Vogel and his successors employed one or other form of measuring machine, provided with a microscope having single or close parallel webs which could be successively pointed on the photographed lines of the star spectrum and the lines of the terrestrial spectrum.
He had no lambskin cap on his head, nor had he a loaded whip over his shoulder, as when Rostov had seen him on the eve of the battle of Austerlitz, but wore a tight new uniform with Russian and foreign Orders, and the Star of St. George on his left breast.
If then the screw-value in kilometres per second is known for the neighbourhood of each of the comparison lines employed, the radial velocity of the star can be independently derived directly from coincidences made in above manner in the neighbourhood of each comparison line.
Regarded as a linear velocity, the parallactic motion is the same for all stars, being exactly equal and opposite to the solar motion; but its amount, as measured by the corresponding angular displacement of the star, is inversely proportional to the distance of the star from the earth, and foreshortening causes it to vary as the sine of the angular distance from the apex.