Fig. 2. by the iron girder at the points a and b. The maximum weight thus thrown on the girder, according to a calculation made at the time, would amount to 2 tons at each of the points where the principal bore upon it; giving a total pressure of 5 tons: this was on the supposition that the weight of the roof itself, and the action of the wind upon it, would prove equivalent to a weight of 40 lbs. on the foot superfi cial. The roof was erected by the contractor who furnished the plan, and had undertaken the work at his own risk. When it arrived on the ground, the slightness of the girders was such as to render it advisable to subject them to necessary proof before proceeding to place them in the work. Accordingly, two girders <------S-----> were placed at a short distance apart, and properly fixed; baulks were then laid across from one to the other, at the two points a and b; and upon these, planks were laid, which carried pigs of iron. They did not show much symptom of weakness until 4 tons were placed on the platform; but with this load, which was less than one-half of what the two should have carried, the two vertical braces, c and d, were broken by a tendency of the under flange of the girder to rise at those points in a direction perpendicular to the curve, and the whole very soon gave way, and was completely smashed. In this case, not only was the metal too thin, but the connecting pieces between the upper and lower flanges were too slight, and too far apart; the top flange was made wider than the bottom, in order to give a bed for the shoe of the principal: had the openings been filled in, the girder might have stood the test, though even then it would have been but slight. Fig. 3 shows two links of a chain guy for supporting a pair of shears, erected for lifting heavy weights, such as boilers, &c.: these links were about 6 feet 6 inches long, and were made of 2-inch round iron they were subjected to the following proof by means of an hydraulic press. With 35 tons, these l two links stretched of an inch. With 40 tons, these of an inch, two links stretched With 60 tons they stretched 34 inches and broke, the metal being clean and sound. In this case the breaking weight Fig. 3. was about double that which might have been fairly placed upon the chain, viz. about 31 tons, which would have been at the rate of 10 tons upon the square inch; for although 35 tons did not apparently cause any set during the time the experiment lasted, yet it is impossible to say that that weight might not have caused such an effect, if left for a sufficient length of time. The following formula is deduced from Mr. Hodgkinson's experiments. "As the distance between the supports in feet is to the depth in feet of the beam in the middle of its length, so is the area in inches of the bottom flange to a fourth quantity, which, when multiplied by a constant number to be determined by experiment, will give the breaking weight in tons." This given number may be taken at 27.3 for common beams; then half of this quantity will be the weight which the girder will bear, if distributed equally over its length. The ratio of the area of the middle section of the top flange to that of the bottom should be about 1 to 4, or 4.5. The diagram (fig. 4) represents a girder of 18-feet bearing: the maximum weight which would ever be thrown upon it, including the weight of a fire-proof floor, was considered to amount to about 200 tbs. on the foot, or 14 tons spread over its length: two of these girders were placed at but a short distance apart from each other, and April 23.-Deflection still the same, the weight having remained undisturbed. April 29.-No alteration had taken place in the deflection, and the weights being removed, the girder resumed its original form, showing no trace of a set or permanent alteration. The section annexed shows the relative proportions of the upper and under flanges of the girder: the top and bottom of the girder were parallel, but the lower flange, being 8 inches broad at the middle, diminished to 4 inches at the point of support. over the whole length, should be its maximum load; whereas it carried 18 tons, or 36 tons placed on two girders, without showing any symptoms of giving. The average weight of a large number of these girders amounted to about 16 cwt. Gland, the pressing piece of a stuffingbox of a steam-engine Glass: this artificial transparent substance was introduced very early. Hollinshed says, an Englishman named Benedict Biscop, who had taken upon him the habit of a monk in Italy, came here with the Archbishop of Rome, in the year 670, and brought painters, glaziers, and other such curious craftsmen into England for the first time. Glasses superseded small drinkingbowls; they were of Venetian manufacture, and probably first brought here in the 16th century. Earlier they do not appear to have been used in England; nor to have come into much fashion till the time of Elizabeth. Glass water-gauge. See Gauge-glass. Glazing, the art of affixing glass to the · sashes of windows, casements, &c., for the purpose of admitting the light of day; anciently applied to the affixing to windows decorative, stained, and painted glass. A great many beautiful examples exist in this and other countries, of early designs, and of examples in the cinque-cento style: for the latter, see Divers Works of Early Masters,' 2 vols. folio, 1846. Glazing is also a term applied to the finishing of a drawing with some thin, transparent, and glossy tint, through which the first colours appear, and are heightened in their effect Glebe, turf, soil; land possessed as part of the revenue of an ecclesiastical benefice Glist, a shining black or brown mineral, of an iron cast Glue, a tenacious viscid matter, which is used as a cement by carpenters, joiners, &c. Glues are found to differ very much from each other in their consistence, colour, taste, smell, and solubility. Some will dissolve in cold water, by agitation; while others are soluble only at the point of ebullition. The best glue is generally admitted to be transparent, and of a brown yellow colour, without either taste or smell. It is perfectly soluble in water, forming a viscous fluid, which when dry preserves both its tenacity and transparency in every part, and has solidity, colour, and viscidity, in proportion to the age and the strength of the animal from which it is produced. To distinguish good glue from bad, it is necessary to hold it between the eye and the light; and if it appears of a strong dark brown colour, and free from cloudy or black spots, it may be pronounced to be good. The best glue may likewise be known by immersing it in cold water for three or four days, and if it swells powerfully without melting, and afterwards regains its former dimensions and properties by being dried, the article is of the best quality. A small portion of finely levigated chalk is sometimes added to the common solution of glue in water, to strengthen it and fit it for standing the weather. A glue that will resist both fire and water may be prepared by mixing a handful of quicklime with four ounces of linseed oil, thoroughly levigated, and then boiled to a good thickness, and kept in the shade, on tin plates, to dry. It may be rendered fit for use by boiling it over a fire in the ordinary manner. Glyphs, perpendicular flutings or channels used in the Doric frieze Gobbets, stones; a measure or quantity, so called in the time of Edward III. Gola, the Italian term for cyma found in many parts of the world, but the greatest quantity of which is obtained from the coast of Guinea. The produce of California remains to be determined. Gold seems to be the most simple of all substances. It is spoken of in Scripture, and the use of it among the ancient Hebrews, in its native and mixed state, and for the same purposes as at present, was very common. The ark of the covenant was overlaid with pure gold; the mercy seat, the vessels and utensils belonging to the tabernacle, and those also of the House of the Lord, as well as the drinkingvessels of Solomon, were formed of this metal. Gold occurs, in the metallic state, mixed with several metals, but more commonly with silver and copper, and sometimes pure. Golden sulphur of antimony, golden yellow, is the hydro-sulphuret of antimony, of an orange colour, which is destroyed by the action of strong light. It is a bad dryer in oil, injurious to many colours, and in no respect an eligible pigment either in oil or water. Gold purple, or Cassius's purple precipitate, the compound oxide which is precipitated upon mixing the solutions of gold and tin. It is not a bright, but a rich and powerful colour, of great durability, varying in degrees of transparency, and in hue from deep crimson to a murrey or dark purple: it is principally used in miniature painting, and may well be employed in enamel painting. Gondola, a Venetian barge much or namented, used in the canals of Venice for the convenience of the inhabitants: the common dimensions are 30 feet by 4 feet: each end is terminated by a very sharp point, which is raised perpendicularly to the full height of a man Goniometer, an instrument for measuring angles and crystals Gorged, in heraldry, the bearing of a crown, coronet, or the like, about the neck of a lion, swan, &c. Gossan, an imperfect iron ore, commonly of a tender rotten substance, and of a red or rusty iron colour Gothic Architecture, usually so called. Both Mr. Britton and Mr. Pugin have treated of it by the name of Christian Architecture.' It had its rise from the Romanesque: this took its origin from Roman remains at the declension of that empire. It became Saxon, then Norman, and varied in its character with the maturity of years. It was Early English, Perpendicular, Decorated, Flamboyant, &c., till it lost its ecclesiastical and monastic character in the Domestic, which prevailed in the Tudor style (Renaissance), followed by the Elizabethan, &c. Gouge, in carpentry, an instrument like a round hollow chisel Governor, the apparatus for regulating the supply of steam to the cylinder so as to give a constant velocity to the engine. It consists of two balls suspended from a vertical spindle, and revolving with it: the suspending rods are connected by arms to a sliding-piece which fits the spindle and acts upon a lever attached to a throttle-valve in the steam-pipe: the balls rise by the centrifugal force as the velocity increases, and close the valve: when the velocity diminishes, the balls fall, and open the valve. Governor, a contrivance for equalizing the motion of mills and machinery, as well as being used as above described Governor balls, the solid metal balls fixed on the ends of the suspending rods of the governor Governor (gas). The governor is a machine for regulating and equalizing the flow of gas from the gasometers to the street-mains, and is much more perfect in its action than any slide-valve applied for that purpose requiring attendance. Its use is no where sufficiently appreciated. Had it been a compli cated piece of machinery, or expensive in its first cost and afterapplication, objections to its adoption would not have been surprising, -but it is perfectly simple, its action is certain and unvarying, and its first cost inconsiderable. The velocity of gas in the mains and pipes of supply is, in the first instance, as various as there are differences in their altitudes and extent. A main at one place will furnish, with a certain pressure of gas, a flame one inch high; while at a different altitude it will furnish a flame double that height. lf, again, in the direction of the main there are many bends, angles, or contractions in its diameter, the velocity of the gas through it will vary considerably more than if it were direct and uniform. If the pipe be of any great length, and of uniform bore, but unequally furnished with branches, the burners will be unequally supplied with gas: those which are near its head will be supplied with a fuller stream of gas than those which are situated towards its termination. Independently of these differences, arising from diversity of local positions, there will always be one great variation in the velocity of the gas, occasioned by the variety of periods during which lights are required by different consumers supplied from the same main or system of pipes: for example, when a certain number of burners is to be supplied, and it happens that one-half are shut off sooner than the rest, the velocity of the gas in the mains will be materially increased, and the remaining lamps should be turned down; but many would not be reduced, and much gas would be lost. Gowan, decomposed granite; but the term is sometimes applied to the solid rock Gozzan, oxide of iron and quartz Grace is taken for beauty, graceful form or agreeableness of person; for form, friendship, and kindness; for certain gifts of God, which He bestows freely, when, where, and on whom He pleases: such are the gifts of miracles, prophecy, language, &c. Grace principally consists in the turn that a painter gives to his objects, to render them agreeable,-even those that are inanimate. It is more seldom found in the face than in the manner; for our manner is produced every moment, and can create surprise. A woman can be beautiful but one way, yet she can be graceful a thousand. Grace is neither found in constrained nor in affected manners, but in a certain freedom and ease between two extremes. Gradation, in painting and drawing, implies the gradual receding of objects into the remote distance, by a proper strength or due diminution of light, shade, and colour, according to their different distances, the quantity of light which shines upon them, and the medium of air through which they are seen Gradient, a deviation from a level surface to an inclined plane Graduation, the division of philo sophical instruments into degrees and other minute parts Grain tin, the finest tin, smelted with charcoal; also the ore of very rich tin sometimes found in the form of grains or pebbles Grange, a monastic farming establishment in ancient times it was common to attach farm-houses and granaries to the estates of religious institutions Granite, a natural stone of great strength, hardness, and durability; much used in building: it is a primary and unstratified rock, consisting of quartz, mica, and felspar, each crystallized and cohering, but without any base or cement Grapnel, in navigation, a sort of small anchor with four or five flukes or claws, commonly used for boats and small vessels |