The following Table exhibits at one view the results of these experiments, which, notwithstanding the objections to the method by which they were obtained, appear to be consistent with each other.

It may be observed here, in anticipation, that the tensile strength is much smaller in the case of glass fractured by a direct strain in the form of bars, than when burst by internal pressure in the form of thin globes. This difference is no doubt mainly due to the fact that thin plates of this material generally possess a higher tenacity than stout bars, which, under the most favourable circumstances, may be but imperfectly annealed. There is also a considerable discrepancy between the strength of green and crown-glass when in the form of bars and when in the form of globes. In the case of the bars, the results are as 1.0 to 1.13 in favour of green glass, whilst in the case of the globes, the results are as 10 to 12 in favour of the crown-glass. These discrepancies may, however, be accounted for from the different condition of the material in relation to annealing in the two cases, or from an imperfect bedding of the specimen, causing a distortion of the strain out of the direction of the axis of the specimen, or from accidental vibration in laying on the weights.

SECTION II.

RESISTANCE OF GLASS TO CRUSHING.

The next series of experiments was instituted with a view of determining the powers of resistance of glass to a direct crushing force. The specimens subjected to experiment were small cylinders (fig. 5) varying in length from

Fig. 5.

1 to 2 inches, and about three-quarters of an inch in diameter. They were placed for the purpose of crushing within the box a (fig. 6), thin packings of soft lead being interposed between the glass and the parallel crushing surfaces of the box and its solid steel piston b; in this way a firm and uniform bearing surface was secured, and the crushing force was applied perpendicularly in the direction of the axis of the specimen. Fig. 6 exhibits the general arrangement of the crushing apparatus, consisting of a lever A, 8 feet long, supported on a strong cast-iron base B, B. The crushing force obtained by placing weights in the scale-pan hung at the extremity of the lever is transmitted through the piston b, to the specimen to be crushed, c.

This specimen having been slightly f early stage in the experiment, it was take fractured side ground flat preparatory to an EXPERIMENT 2.

The same specimen as in Experime

Crushed with 13,033 lbs.=23,483 lbs. pe

E 4

It will not be necessary again to repeat in detail the steps by which the weights were augmented, as these were similar in every case. In the succeeding experiments the weights at which the specimens fractured and crushed are alone given.

Crushed suddenly with 5193 lbs. 13,494 lbs. per

square inch.

EXPERIMENT 5.

=

=

Crushed suddenly with 11,241 lbs.=20,775 lbs. per

square inch.

Crushed with 11,913 lbs. 32,803 lbs. per square inch.

=

*This experiment is so evidently anomalous, that there can be little doubt that the bedding surfaces were not parallel; hence this result is omitted in the following averages.