thickness, we find, by dividing equation (12) by the above,

When k=043, as in most of the experiments on iron,

then

Р 11

=

P' 12

; that is, in this case, the strengths of the

two cylinders will be nearly equal to one another.

II. Generalisation of the Results of the Experiments on the Resistance of Glass Globes, Cylinders, and Ellipsoids to Internal Pressure.

Let D=the diameter of the globe or cylinder, as the case may be.

k=the thickness of the material in inches.

a=the longitudinal sectional area of the material
in square inches; that is, in the direction of
the line of rupture, or line of minimum
strength.

A=the longitudinal section in square inches.
P=the bursting pressure in lbs. per square inch.
Tthe tenacity of the material in lbs. per square
inch.

PA.

that is,

a

a

is a constant for vessels of the same material.

This theoretical deduction is fully confirmed by the results of these experiments, as arranged in the following Table:

:

TABLE XIV.-Resistance of Glass Globes, Cylinders, and Ellipsoids to an Internal Pressure.

The general equation (15), giving the bursting pressure in pounds per square inch, then becomes

T2

eneralisation of the Results of Experiments on the
ensile and Compressive Resistances of Glass.
tenacity (T1) of glass in the form of bars
86+2540+2890+2540)=2560 lbs. per sq. in. ;
tenacity (T',) of glass in the form of thin plates
00+4800+6000)=5000 lbs. per square inch;

T' 5000 =2 nearly,
Ꭲ, 2560

he tenacity of glass in the form of thin plates is
ice that of glass in the form of bars.

resistance (T2) of glass to compression
7582+31876+31003)=30,150 lbs. per sq. in. ;

he ultimate resistance of glass to a crushing force twelve times its resistance to extension.

stance of Rectangular Glass Bars to a Transverse Strain.

=the length of the bar supported at the ends and

loaded in the middle.

-breaking weight in lbs.

K=area of the whole transverse section.

D= the whole depth of the section.

d, d1=the respective distances of the top and bottom edges from the neutral axis.

T1the tensile resistance of the material in lbs. per square inch.

2

T2 the compressive resistance of the material in lbs. per square inch.

Then we have TATE'S "Strength of materials," equations (27) and (6)—

Substituting this value of the constant, equation (16)

which expresses the transverse strength of a rectangular bar of glass supported at the ends and loaded in the middle.

III.

RESEARCHES ON THE TENSILE STRENGTH OF WROUGHT

IRON AT VARIOUS TEMPERATURES.

(From the Report of the British Association for 1856.)

ON a previous occasion I had the honour of conducting, for the Association, a series of experiments to determine the effects of temperature on the strength of cast iron. In that inquiry I endeavoured to show to what extent the cohesion of that material was affected by change of temperature, and taking into account the rapidity with which iron imbibes caloric, and the facility with which it parts with it, it is equally interesting to know to what extent wrought iron is improved or deteriorated by similar changes. In the present inquiry, as in the former on cast iron, the expansion of the metal by heat is not the question for solution. Rondelet, Smeaton, and others, have already investigated that subject, and it now only remains for us to determine the effects produced on the strength of malleable iron by changes of temperature varying from -30° of Fahrenheit to a red heat, perceptible in daylight.

The immense number of purposes to which iron is applied, and the changes of temperature to which it is exposed, render the present inquiry not only interesting, but absolutely essential to a knowledge of its security under the varied influences of those changes; and when it is known that most of our iron constructions are exposed to a range of temperature varying from the extreme cold of winter to the intense heat of summer, it is assuredly de