PROCEEDINGS OF SOCIETIES. 
75 
in relief. The peculiar property of it is, that if the polished side be used to reflect 
the rays of the sun on any plain surface, the reflection presents a perfect image of 
the figures on the other side. This singular phenomenon has been explained in two 
ways. Sir John Davis, the author of a work entitled “The Chinese: a General 
Description of China and its Inhabitants,” says that the effect is produced by etching 
on the convex side a copy of the figures on the other; that the surface is then highly 
polished upon some soft, yielding substance, as cloth, so that the hollows may be 
polished equally with the rest of the surface ; and that this etching is so light that 
the figures will only be visible in very strong lights. 
Professor Farada} r supposes that the mirror is cast in what is technically called a 
“ chill,” that, consequently, the density of the thick parts of the mirror is less than 
that of the thin portion ; that the surface in the process of polishing grinds away 
unequally, as the denser parts will resist the grinding more than the other; that 
thus hollows are produced on the convex surface corresponding in position to the 
figures on the back, and that these form concave mirrors, which reflect the images 
as described above. 
At Mr. Patterson’s request, Mr. William Gray, a member of the society, under¬ 
took to make a small casting to test, from actual experiment, the effect of a “ chill.” 
His experiments, however, were not sufficiently extensive to enable him to arrive 
at any satisfactory conclusion on that head ; but, from the difficulty he experienced 
in getting the metals composing the alloy thoroughly mixed, he thought that the 
unequal density on the metal, arising from imperfect mixture, would materially in¬ 
terfere with like unequal density arising from the mode of casting. Hence he in¬ 
ferred that the less dense portions of the convex surface would not invariably cor¬ 
respond in position to the figures on the back, and he suggested that, after the mirror 
had been cast in a “ chill,” as Professor Faraday supposed, the upper surface was sub¬ 
jected to some such process as that described by Sir J. Davis. By this means slight 
hollows would be produced in proper positions ; and, afterwards, in the process of 
grinding, the hollows would become greater when the density had varied according 
to the law laid down by Faraday, and the inequalities of surface produced by the 
acid in those parts of it where the density was regular would not be diminished by 
grinding the surface on cloth. 
Mr. MacAdam read some notes on Physical Geography, relating to the distri¬ 
bution of the great masses of land on the surface of the globe, and referred to some 
theories which had been started in explanation. 
Mr. Patterson laid on the table a number of engravings of Lycian coins, and read 
the following announcement respecting them :—“ Sir Charles Fellows, being about 
to publish some account of relative dates of the works of art discovered by him in 
Lycia, is anxious to perfect, as far as possible, the portion illustrated by the ancient 
coins of that province. Sir Charles sends impressions from the plates he is preparing, 
and asks assistance in making additions or corrections, that he may be enabled to 
to bring together, he believes for the first time, all the coins of Lycia before the age 
of Alexander the Great.” 
DUBLIN NATURAL HISTORY SOCIETY. 
FEBRUARY 10, 1854. 
Dr. Gordon, M.R.I.A., in the chair. 
The usual routine business being disposed of, Mr. Kinahan presented to the 
Society two volumes of Pennant’s “ British Zoology.” 
Mr. Callwell, in proposing a vote of thanks for the donation, observed that works 
of such a class were valuable to the Society as records of the state of zoology of that 
day, and as comparison withh the present superiority of all works of the kind, and 
of the advanced state of scientific research. The works of Pennant, however, are 
well known for the accuracy of his details. 
