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Observatory in place of camphine lamps for the photographic
registration of magnetic variations, &c. In a very short time
the surface of every reflector was destroyed, and the drawtubes
of the telescopes quite corroded. It was found necessary
to place a tube over each burner, and to connect all these with
a central chimney in which a strong draught was maintained
to carry off the products of combustion. These tubes were,
for cheapness, made of zinc. In a few days all the lamps
were found extinguished by a crystaline substance which
dropped on the burners from the tubes. This proved to be
sulphate of zinc. I recommended the substitution of tinned
copper tubes, but the price was objected to, and a contrivance
was resorted to by which the condensed matter was run into
a vessel at the side of tho chimney. In one of these vessels I
collected, in six woeks, from a burner consuming about halfa-foot
per hour, 3/4-11). sulphate of zinc. In this case unusual
means were used to carry off the acid in the state of vapour,
but with what effect the result showed. This result fully
confirms all the statements made by boot-makers and others
of the rotting effects of the products of gas combustion. It
will be observed that at the Observatory there was simply
the substitution of one combustible for another (gas for
camphine), no greater number of burners being employed
after gas was introduced, and the flames of both the gas and
the camphine being of the same size. Carbonic acid and
water must have been as abundantly produced by the
camphine as by the gas, yet no ill effects were produced,
though it was burnt for at least a year, while a week sufficed
to show the destructive effects of the gas. Dr. Odling makes
much of the difference between gas burned slowlv and at the
ordinary rate, and might, perhaps, attribute some of the above
results to the smallness of the flames employed. If so, I
would reply, that as these flames were required to give as
much light as possible, the supply of air was certainly not
more abundant than in an ordinary gas flame; so that no
greater amount of oxidation was likely to take place. I will
further state, that I examined the liquid which condensed in