484 Transactions. — Miscellaneous. 



round like a stick, but ouly 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 the comet. 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. 



Aet. LXI. — Macquarie Island. By John H. Scott, M.D., F.E.S.E., 



Professor of Anatomy and Physiology in the University of Otago. 

 {Bead before the Otago Institute, 21st June, 1881 and 9th May, 1882.] 

 Plate XXXIX. 

 In 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 American 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, 



