lanetary movement betrays
itself in a comparatively short time by turning the imprinted image of
the object affected by it from a dot into a trail.

In the arduous matter of determining star distances progress has been
steady, and bids fair to become rapidly accelerated. Together, yet
independently, Gill and Elkin carried out, at the Cape Observatory in
1882-83, an investigation of remarkable accuracy into the parallaxes of
nine southern stars. One of these was the famous Alpha Centauri,
the distance of which from the earth was ascertained to be just
one-third greater than Henderson had made it. The parallax of Sirius, on
the other hand, was doubled, or its distance halved; while Canopus
proved to be quite immeasurably remote--a circumstance which,
considering that, among all the stellar multitude, it is outshone only
by the radiant Dog-star, gives a stupendous idea of its real splendour
and dimensions.

Inquiries of this kind were, for some years, successfully pursued at the
observatory of Dunsink, near Dublin. Annual perspective displacements
were by Dr. Bruennow detected in several stars, and in others remeasured
with a care which inspired just confidence. His parallax for Alpha
Lyrae (0.13") was authentic, though slightly too large (Elkin's final
results gave Pi = 0.082"); and the received value for the
parallax of the swiftly travelling star "Groombridge 1,830" scarcely
differs from that arrived at by him in 1871 (Pi = 0.09"). His
successor as Astronomer-Royal for Ireland, Sir Robert Stawell Ball (now
Lowndean Professor of Astronomy in the University of Cambridge), has
done good service in the same department. For besides verifying
approximately Struve's parallax of half a second of arc for 61 Cygni, he
refuted, in 1811, by a sweeping search for (so-called) "large"
parallaxes, certain baseless conjectures of comparative nearness to the
earth, in the case of red and temporary stars.[1580] Of 450 objects thus
cursorily examined, only one star of the seventh magnitude, numbered
1,618 in Groombridge's Circumpolar Catalogue, gave signs of measurable
vicinity. Similarly, a reconnaissance among rapidly moving stars lately
made by Dr. Chase with the Yale heliometer[1581] yielded no really
large, and only eight appreciable parallaxes among the 92 subjects of
his experiments.

A second campaign in stellar parallax was undertaken by Gill and Elkin
in 1887. But this time the two observers were in opposite hemispheres.
Both