The Locomotive - Lighthouse Survival Blog

is'.i i
rii |
i: locomotiv i: 89
plants, running under forced draft, are given at the end of the paper. We think Mr.
Ronev is :i Little over-sanguine about mechanical draft, but, neverthi found bis
paper of considerable interest
.
i>n June i:">. the Royal Society gave a Boiree, to which ladies were invited. A
number f interesting things were exhibited. Mr. J. \Y. Swan showed some specimens
of gold leaf prepared bj him, which arc only tour one-millionths (.000,004) of an inch
thick. They wen- made by electro-plating with gold on Borne of the wonderfully thin
sheets of copper that Mr. Swan produced in a similar manner, some years ago. After
the gold had been deposited, the copper foil was dissolved awaj by perchloride of iron,
leaving only the gold. The gold-leaf so prepared has a thickness of from one-fifth to
one tenth that of the thinnest films that can be produced by the old-fashioned pn
of beating. Mr. J. W. Kearton exhibited some "magic minors" which he had made
These mirrors are metallic, and look perfectly plain. When a ray of sunlight is re-
flected from them to a screen, however, a pattern appears on the screen in dusky lines.
These "magic mirrors" were invented by the Japanese, who engrave a pattern on the
hack of the mirror, and then polish the front. "The portions corresponding to the
raised parts on the back stand up more rigidly to the polishing tool, and therefore
sutler a great er reduction, the evidence of which is afforded by the reflected beam."
Mr. Kearton's mirrors are prepared in a different manner. lie etches the pattern on the
face of the mirror, and then polishes the mirror till the pattern is no longer visible. It
will still show, however, when the ray of sunlight is reflected on a screen. Professor
C. V. Boys showed photographs of the apparatus used by him to determine the aver-
age specific gravity of the earth, the apparatus itself being too delicate to be brought
to the hall for exhibition. His method is substantially the same as that used by Cav-
endish, a century ago, except that the present apparatus is far more delicate and accu-
rate. Professor Boys has been working on this problem for live years, and lie finds that
the specific gravity of the earth, taken as a whole, is 5.527. It i.s believed that this
result is correct to within one-fiftieth of one per cent. It is certainly by far the best
determination of the specific gravity of the earth that has yet been made.
Professor Dewar, an eminent English scientist, has recently been investigating
the phenomena attending the production of great cold, and many of his lecture experi-
ments have been striking and beautiful. In one instance he caused a soap bubble to
float down into a vessel of liquid air. The intense cold froze the bubble, and the pro-
fessor cracked it in two. The halves continued to float like egg-shells on the surface
of the liquified air, and they gradually filled with snow, which was precipitated by
the cold from the moisture in the air of the room. His method of transporting liquid
air deserves mention. He uses a double walled glass vessel, the space between the
walls being completely exhausted by a good air-pump. A few drops of mercury are
then introduced into the vacuum jacket so formed, and the liquid air is poured into the
inner vessel. The slight vapor arising from the mercury is instantly condensed on the
inner vessel, forming a coating of mercury of great brilliance. The vacuum jacket is
an almost perfect non-conductor of heat, and the mercury film reflects nearly all the
radiant heat that strikes the vessel. The liquified air in the inner compartment is
therefore well protected; but to make the protection more perfect still, Professor
Dewar packs the whole apparatus in solid carbonic acid gas!