484 Transactions.— Miscellaneous. 
round like a stick, but only like a jet of water from a hydrant. The 
curvature would, therefore, afford data for finding the velocity with which 
the repelled matter was driven off. 
Again, the convex, or front side of the tail is brightest and straightest. 
In Donati’s comet, 1858, small straight tails preceded the main tail. 
One explanation serves for all these facts. The sun analyzes the matter 
of thecomet. Some parts of it he can dart away at an incomparably higher 
velocity than others. This matter, most swiftly ejected, either makes sepa- 
rate straight tails, as in 1858, or somewhat straightens and brightens the 
convex, or front, side of the main tail. 
There is much room for speculation and enquiry in connection with this 
repulsive force. Does it pursue the repelled matter, and drive it away with 
an ever-increasing motion, so that it will leave our system altogether, or 
does it give an initial impulse, and have done? Will the repelled matter 
change its condition by cooling, and cease to be liable to the persecution of 
the repelling force? Or has it lost its affinities and the power of changing 
its condition? Whatever may be its destiny it is certainly divorced from 
the comet for ever. - 
There is reason to suppose that all the matter of a comet is not suscep- 
tible to this repulsive force, and that a sufficient number of perihelion 
` passages will sift all the susceptible matter out, and leave the comet inca- 
pable of producing a tail. Hence almost all the short-period comets that 
are in perihelio every few years are tailless ; while visitors from the eterni- 
ties of space, who can only be in that sifting position once in ten or twenty 
millions of years, frequently make a prodigious display of tail. 
Arr. LXI.—Macquarie Island. By Jous H. Scorr, M.D., F.R.S.E., 
Professor of Anatomy and Physiology in the University of Otago. 
[Read before the Otago Institute, 21st June, 1881 and 9th May, 1882.) 
Plate XXXIX. 
Ix most of the maps which I have seen, an island named “Emerald” is put 
down in latitude 57?, a long way to the south of Macquarie Island. This, 
is, however, now generally regarded as mythical, for its supposed site was 
sailed over by the Ameriean Transit of Venus Expedition and no land was 
observed. In all probability its discoverers mistook an iceberg for snow- 
covered land, a not unlikely mistake in misty weather. 
We may therefore safely consider that Macquarie Island is the most 
southerly island of the outlying members of the New Zealand group, indeed, 
