tive to gaslight are by no
means necessarily the most sensitive to daylight; in several instances,
in fact, the reverse seems to be true.

It should be said that the above figures cannot be considered final until
each plate has been tested separately with its own developer, as this
would undoubtedly have some influence on the final result.

Meanwhile, two or three interesting investigations naturally suggest
themselves; to determine, for instance, the relative actinism of blue
sky, haze, and clouds; also, the relative exposures proper to give at
different hours of the day, at different seasons of the year, and in
different countries. A somewhat prolonged research would indicate what
effect the presence of sunspots had on solar radiation--whether it was
increased or diminished.

* * * * *

NATURAL GAS FUEL AND ITS APPLICATION TO MANUFACTURING
PURPOSES.

[Footnote: Read before the Iron and Steel Institute of London, May 8,
1885.]

By Mr. ANDREW CARNEGIE, New York.

In these days of depression in manufacturing, the world over, it is
specially cheering to be able to dwell upon something of a pleasant
character. Listen, therefore, while I tell you about the natural gas fuel
which we have recently discovered in the Pittsburg district. That
Pittsburg should have been still further favored in the matter of fuel
seems rather unfair, for she has long been noted for the cheapest fuel in
the world. The actual cost of coal, to such as mine their own, has been
between 4s. and 5s. per ton; while slack, which has always been very
largely used for making gas in Siemens furnaces and under boilers, has
ranged from 2s. to 2s. 6d. per ton. Some mills situated near the mines or
upon the rivers for many years received slack coal at a cost not
exceeding 1s. 6d. per ton. It is this cheap fuel which natural gas has
come to supplant. It is now many years since the pumping engines at oil
wells were first run by gas, obtained in small quantities from many of
the holes which failed to yield oil. In several cases immense gas wells
were found near the oil district; but some years elapsed before there
occurred to any one the idea of piping it to the nearest manufacturing
establishments, which were those about Pittsburg. Several years ago the
product of several gas wells in the Butler region was piped to two mills
at Sharpsburg, five miles from the city of Pittsburg, and there used as
fuel, but not with su