The following table gives the absolute sensitiveness of several of the best known kinds of American and foreign plates, when developed with oxalate, in terms of pure silver chloride taken as a standard.  As the numbers would be very large, however, if the chloride were taken as a unit, it was thought better to give them in even hundred thousands.

SENSITIVENESS OF PLATES.

Plates.  Daylight.  Gaslight. 
Carbutt transparency 0.7 .. 
Allen and Rowell 1.3 150
Richardson standard 1.3 10
Marshall and Blair 2.7 140
Blair instantaneous 3.0 140
Carbutt special 4.0 20
Monroe 4.0 25
Wratten and Wainwright 4.0 10
Eastman special 5.3 30
Richardson instantaneous 5.3 20
Walker Reid and Inglis 11.0 600
Edwards 11.0 20
Monckhoven 16.0 120
Beebe 16.0 20
Cramer 16.0 120

It will be noted that the plates most sensitive 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.