SCIENTIFIC SUMMARY* 
107 
galvanically is stated to be a silver-grey coloured, velvety-looking, very 
finely-grained mass, of 7*675 sp. gr. at 15°; this metal is so hard that it 
scratches glass, but is, also, very brittle. When this metal was very care- 
fully ignited in a covered platinum crucible, its colour became deeper, its 
hardness and brittleness were lost, and its sp. gr. had increased to 7*811, 
which is higher than that of wrought iron. The fact of this increase of 
specific gravity led the author to conclude that the iron might contain gas 
absorbed in its substance. A quantity of 9 730 grms. were treated in a 
Sprengel’s aspirator, with the result that, aided by an increased tempera- 
ture, which was carried to dulhred heat, 17*76 volumes of gas, chiefly com- 
posed of hydrogen, were obtained from the quantity of iron submitted to 
experiment. Vide Bulletin de VAcademie imperiale des Sciences de St. - Peters- 
bourg. 
The Value of Mercurial Thermometers. — M. Bosscha lately sent to the 
French Academy an account of a mercurial thermometer of a peculiar form. 
M. Regnault in commenting on it thinks it is impossible to lay down rules 
for the registration of mercurial thermometers ; the only exact instrument 
suited for experiments requiring precision is the air thermometer. This is, 
however, an inconvenient instrument, and therefore M. Regnault recom- 
mends that it be used only as a standard with which to compare the mer- 
curial instruments. — Comptes rendus, Oct. 18, 
The Electric Resistance of Platinum. — Herr Stefan, in a note to the Vienna 
Academy on the electric resistance of plates of platinum, stated that the 
results of his experiments accord with the theories of KirchhotF. 
The Office of the late Professor Graham. — It is unfortunate for science that 
another of its few rewards has gone. The Mastership of the Mint is an 
extinct office. No successor to Graham will be appointed. 
Graham! s Labours will form the subject of a Friday evening’s discussion 
(before Easter) by Dr. Odling, at the Royal Institution. 
Lectures on Light. — Dr. Tyndall’s “juvenile” lectures commence just as 
we go to press, and will be continued for some days during the month of 
January. 
The Rotation of a Rigid Body about a Fixed Point is the title of the paper 
by Professor P. G. Tait, which has just obtained the Keith medal of the 
Royal Society of Edinburgh. 
Examination of Transparent Substances by Polarised Light. — A very instruc- 
tive paper, from which our microscopical readers may gather a hint or two, 
was lately laid before the French Academy by M. Lallemand. The author 
gives instructions as to how to obtain several polariscopic effects. In order 
to see the illumination of any fluid — water, for instance — it is poured into a 
glass tube, which is closed at both ends by means of pieces of plate glass : 
the tube is then placed in a dark chamber in a horizontal position, and a ray 
of polarised light is made to shine upon the tube, which, when looked at 
sideways, will exhibit a vivid glimmering ; but, seen in any other direction, 
the tube remains dark. Hence, it follows that the propagation of the light 
takes place in the direction of the plane of polarisation ; and it also follows 
that the vibrations of the waves of the ether take place in the perpendicular 
direction. When, instead of Water, any other fluid is taken which is endowed 
with rotatory power — a solution of sugar, for instance — a very beautiful chro- 
