496 
MESSES. LOCKYEE AND EOBEETS ON THE QUANTITATIVE 
the following experiments were made with a view to determine what details of mani- 
pulation would give the most satisfactory results. 
In the first attempts a fragment of the alloy of a more or less irregular shape was 
simply held in a suitable clip, and a spark-current passed from the alloy to a similar 
Horizontal adjusting-screws. 
D. Revolving table. 
E. Insulating glass rod. 
F. Fixed terminal. 
x. Series of assay-pieces. 
m, n. Wires from induction-coil. 
fragment of aluminium or other metal. We then adopted a method orally suggested 
to one of us by Professor Stokes, which consists in the passage of the spark-current in 
a vertical line across the shortest distance between two cylinders arranged in a horizontal 
position, with their axes at right angles to each other. 
The use of these cylinders was attended with many difficulties, and we substituted for 
them strips of metal cut in the form indicated in the figure (at x). 
The distance between the poles was at first adjusted by a gauge, and subsequently by 
a cathetometer ; but the most accurate results were obtained by placing the portion of 
alloy in the field of a microscope furnished with a 3- or 4-inch objective, a simple 
mechanical arrangement, shown above, bringing the surface from which the spark would 
pass to the point of intersection of two spider-lines in the eyepiece of the microscope. 
We were careful to select alloys which were homogeneous in character; and our 
attention was first devoted to observations on the zinc-cadmium alloy, one of a series of 
