NOTE. The last three cubes of common brick continued to support the weight, although cracked in all directions; they fell to pieces when the load was removed. All the brickwork began to show irregular cracks a considerable time before it gave way.

The average weight supported by these bricks was 33.5 tons per square foot, equal to a column 583.69 feet high,

of such brickwork.

SANDSTONE.

No. 6.-3-in. cube red sandstone, weighing 1 lb. 14 oz., set between boards (made quite dry by being kept in an inhabited room). Crushed with 8 tons 4 cwt. 0 qr.

19 lbs.

lbs. per square inch.

=2043-0

No. 7.-3-in. cube sandstone, weighing 1 lb. 14 ozs., set in cement (moderately damp). Crushed with 5 tons 3 cwt. 1 qr. 1 lb.. =1285-0 No. 8.-3-in. sandstone, weighing 1 lb. 151⁄2 ozs., setin cement (made very wet). Crushed

with 4 tons 7 cwt. O qr. 21 lbs.

No. 9.-6-in. cube sandstone, weighing 18 lbs., set in cement. Crushed with 63 tons 1 cwt. 2 qrs. 6 lbs.

=1085.0

No. 10.-91-in. cube sandstone, weighing 58 lbs., set in cement (77 tons were placed upon this without effect, 2042 lbs. per square inch, which was as much as the machine would carry).

Mean.

=

=3924.8

2185.0

All the sandstones gave way suddenly, and without any previous cracking or warning. The 3-in. cubes appeared of ordinary description; the 6-in. was fine grained, and

appeared tough and of superior quality. After fracture· the upper part generally retained the form of an inverted square pyramid about 24-in. high and very symmetrical, the sides bulging away in pieces all round. The average weight of this material was 130 lbs. 10 ozs. per cube foot, or 17 feet per ton.

The average weight required to crush this sandstone is 134 tons per square foot, equal to a column 2351 feet high of such sandstone,

LIMESTONE.

No. 11.--3-in. cube Anglesea limestone, weighing 2 lbs. 10 ozs., set between boards. Crushed with 26 tons 11 cwt. 3 qrs.

9 lbs..

This stone formed numerous cracks and splinters all round, and was considered crushed; but on removing the weight about two-thirds of its area were found uninjured.

No. 12.-3-in. limestone, weighing 2 lbs. 9 ozs., set between deal boards.

32 tons 6 cwt. O qr. 1 lb.

lbs. per square inch.

=6618.0

Crushed with

=8039.0

This stone also began to splinter externally with 25 tons (or 6220 lbs. per square inch), but ultimately bore as above.

No. 13.-3-in. limestone, weighing 2 lbs. 9 ozs., set in deal boards. Crushed with 30 tons 18 cwt. 3 qrs. 24 lbs.

No. 14.-Three separate 1-in. cubes limestone, weighing 2 lbs. 9 ozs., set in deal boards.

=7702.6

Crushed with 9 tons 7 cwt. 1 qr. 14 lbs.

=6995.3

All crushed simultaneously.

Mean

7338-2

All the limestones formed perpendicular cracks and splinters a long time before they crushed.

Weight of the material from above = 165 lbs. 5 ozs. per cubic foot, or 13 feet per ton.

The weight required to crush this limestone is 471.15 tons per square foot, equal to a column 6433 feet high of such material.

Previously to the experiments just recorded, it was deemed advisable not to trust to the resisting powers of the material of which the towers of either bridge were composed; and, to make security doubly sure, it was ultimately arranged to rest the tubes upon horizontal and transverse beams of great strength, and by increasing the area subject to compression, the splitting or crushing of the masonry might be prevented. This was done with great care, and the result is the present stability of those important structures.

In conclusion, the following general summary of results, obtained from various materials, shows their respective powers of resistance to forces tending to crush them.

The above summary gives pretty correct data for the guidance of the practical builder in the application of these materials when subjected to a simple crushing force. The experiments might be greatly extended to stone from other localities, but the specimens are of a sufficiently varied character to afford the necessary information to those employed in the constructive arts.

145

PART II.

LECTURES.

LECTURE I.

ON POPULAR EDUCATION.

THE object I have in view in this address is to direct your attention to certain principles which I hold to be true, and which I consider essential to the development of the human mind, the formation of character, and the right exercise of our duties to society. In the investigation of the all-important question of education, I hope you will give me your attention whilst I endeavour to lay before you such. facts as seem to elucidate a subject on which no two men appear to be agreed, and which has occupied the attention. of the statesman and philanthropist from the earliest period of our history down to the present time. Notwithstanding the number of treatises that have been written, and the number of speeches that have been delivered, we are still far short of a sound national system of education; and it appears questionable, as society is constituted in this country, whether any system which may be called national would ever supply the wants of the different classes into which the population of the kingdom is divided. Many

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