. IRQ

39

ISI

fflanent level, 102 feet above high water mark, were com-pleted.

The entire completion of this celebrated structure, thebonder and admiration not of a kingdom only, but of theworld, perfects the communication between England andthe sister country. The interchange of transit, and convey-ance of correspondence between their respective capitals, mayhe daily within the compass of ten or twelve hours. Thistapulity of locomotion in the present day may be well con-tested with the slow doings of former times. In 1685 it°ok the then Lord Clarendon, at that time Lord-Lieutenant°t Ireland , from six o’clock in the morning to three in the‘ [ternoon, nine hours, to get from Conway to Bangor , a■stance of 14 miles, while a short time since the distanceaccomplished by the present Lord Clarendon, Lord-■hneutenant of Ireland , in exactly twenty minutes. At the®nme period it took a king’s messenger, “ by express,” sixa ys to get over the ground now traversed between London an d Chester, 188 miles, in five hours; and it is but twentyy e ars since, that the same distance by coach took more thanwenty-four hours.

These are the immediate advantages ; the prospective onesc °nsist in the completion of the great harbour of Holyhead,riow being constructed for the Admiralty by Mr. Rendel the® n g'neer, the pier at which is completed, and the breakwatercommencing the vast operations fixed. Should theumiralty, as has been long expected, on the completion ofin» * lai k° ur > remove to it the West India packets, now start-„ 8 from Southampton, and the Galway line of railway be, 'shed, the voyage to the United States by this route woulde ®k°rtened four or five days.

" e cannot close this article, and necessarily imperfectth 0Unt ’ Britannia bridge, without a passing allusion toUnfortunate difference that occurred during its progress,be ) Veen Messrs. Stephenson and Fairbairn. It is greatly toto t| arnent<!(1 > that men so eminent for talent should differ asgQ leir respective claims to the conception and execution ofclaf ran ^ a wor h- It is not for us to presume to settle suchhut surely each possesses in himself merit so surpassing0 f nai 7 minds, that he may well afford to yield a portion■U t i° n ° ur to the many competitors who may join with himt'on f FaCe ^° r I ame ‘ A work like this might afford distinc-^ tor many minds, and varied talents ; to all give honour,the 6 ^ ^. onour is due. Let us then award to a Stephensoni?aii aier * t justly due to him for his original conception ; to aR hilit ai1 "’ ti' e unwearied perseverance and the vast practicalp er j. y>. b y which that conception was realized and brought tol-^ciff tl0ri > to all associated in the undertaking, each in hisIro^ the merit of talent, zeal, and untiring industry.ar e v N pieces of iron linked together. Iron chains

Wh ere e 'T serv >ceable under the roofs of circular buildings,of s . there is no intermediate tie, particularly at the bottomPushi 116 ^ omes > ■■■ order to prevent them from spreading orbe gl ,? out the walls, which, without this precaution, mightsup D ■i ect to separation, especially when the dome has toSt. p/ i, an ■■umense turret or lantern of stone. The dome ofage 0 p U p S Cathedral, London has two chains let into a bond-Ihotf p ^ an ^ ®tone laid for the purpose.n° w k Girders. Girders of wrought and cast iron haveing s> ^ en use d for some years in the construction of build-hrid'o-g, Ut m ° re especially in the formation of railwayshow j’ o Stati °ns, &c. The article on iron bridges willV ai , 0U8 T ext ensively they have been applied in that way.pus metl° r ,i mS Seders have been recommended, and vari-' r ° n , but S su r gested °f combining wrought with cast■he Use 0 ^.' ese . improvements have been more directed to0 gtrders in the construction of railway and

other bridges, than in buildings. Cast-iron beams forwarehouses, and other large buildings, have been used withsuccess.

Iron King-Posts and Queen-Posts, are in many in-stances preferable to those constructed of wood, and are notmore expensive where both bolts and straps are used.

Iron Stone, an ore of iron composed of iron combinedwith oxygen, silex, carbonic acid, and water. When of asuperior quality, it yields near 40 per cent, of iron. InMissouri, United States , iron stone has been found yielding75 per cent, of metal.

Iron Wood, the popular name of some species of a genusof trees distinguished for their hardness. The diospyrusebenus, or ebony, is sometimes called ironwood.

IRREGULAR, in the art of building, a term applied notonly to the parts of an edifice which deviate from the pro-portions established by antique monuments ; as when theGrecian-Doric is made more than six diameters in height,the Ionic more than nine, and the Corinthian more than ten;but also to places where the angles are unequal, and to jedifices whose counterparts do not correspond in the several :elevations. [

A column is said to be irregular, not only when it deviates ifrom the proportions of any of the three regular orders ; butwhen its ornaments, whether in the shaft or capital, deviate ; jfrom the established forms peculiar to the order.

Irregular Bodies, solids not terminated by equal and [ ;

similar surfaces. j

Irregular Figure, a figure whose sides and angles are j ,

not equal. | |

Irrigation, in agriculture, the art of causing water, byartificial means, to be distributed over the surface of the land,to afford moisture to the plants, &c., where insufficiently :supplied with it by nature. Of late years a practice hasbeen adopted, and with great success, of irrigating landssituated near large towns with the sewage-water diverted ■from the sewers, and conveyed by means of pipes to the ;required spot. The distribution is then effected in various iways, according to the nature of the ground to be irrigated,and other circumstances.

ISAGON, (from the Greek, iaoc, equal, and ywvia, an angle,)in geometry, a figure consisting of equal angles.

ISIAC TABLE, one of the most considerable monumentsof antiquity, being a plate of copper or brass, discovered atRome , in 1525, and supposed, by the various figures in basrelief upon it, to represent the feasts of Isis, and other Egyp - .tian deities.

With regard to the history of this monument, we may ,observe, that the copper or brass ground was overlaid with 1a black enamel, artificially intermixed with small plates of !silver. When, in the year 1525, the constable of Bourbon jtook the city of Rome , a locksmith bought it of a soldier,and then sold it to Cardinal Bembo, after whose death it came !into the hands of the Duke of Mantua, and was kept in thatfamily till it was lost at the taking of that city by the ;Imperialists , in the year 1630, nor has it been ever heard of jsince. By good fortune it had been engraved in its full jproportion, and with all possible exactness, by JEneas Yico \of Parma. This tablet was divided into three horizontal 1compartments, in each of which were different scenes, con- !taining different actions. These compartments are, as it | ■were, different cartouches, distinguished sometimes by single, j jstrokes only, but oftener by a very large fascia, which is full ; !of hieroglyphics, that is, of that mysterious writing, conse- |crated by the ancient Egyptians to the mysteries of religion. j

The four sides of the table were enclosed with a border j

filled up, like the ground, with several figures of the Egyp- I

)