day and then tied into a knot and immersed in boiling water until they become white, when they are hung up in the shade and afterward bleached for several days. The straw is then distributed through the districts, especially in Peru, where the manufacture is carried on. Whole colonies of Indians are engaged in this manufacture. The men, women, and children plait the straw upon a block of wood which they hold between their knees, finishing an ordinary hat in two or three days; but the finest hats occupy several months to complete them, and require especial care in the selection of the straw and the plaiting. The best are made in Ecuador. STRAWBERRY, a well known wild and cultivated fruit, the Anglo-Saxon name of which, streawberige or streowberie, was probably derived from the straw-like stems of the plant or from the berries lying strewn on the ground. The several species belong to the genus fragaria (from the ancient Latin name fraga), of the rose family; they are stemless perennial herbs, with compound leaves of three obovate, wedge-shaped, coarsely serrate leaflets, and multiply by runners, which are long weak branches, forming a bud at the end which soon develops roots and leaves, and by the decay of the branch connecting it with the parent becomes an independent plant. The flowers are in a cyme at the end of an erect scape, with a five-lobed, spreading, persistent calyx, and as many bractlets alternating, and thus appearing ten-cleft; petals (mostly white) five; stamens numerous; pistils simple, seated upon a convex receptacle, which when the ovaries are ripe is greatly enlarged, becoming pulpy and edible, and is popularly regarded as the fruit; it is really the much altered end of the stem (see PLANT), while the true fruits are the small seed-like akenes, the ripened ovaries, which are scattered over its surface or sunk in little depressions. By abortion of the stamens some of the species become more or less dioecious.The strawberry is found in all temperate parts Section of Flower and Fruit. of the northern hemisphere and in the mountains of South America. While Bentham and Hooker state that there are not more than three or four well defined species, a dozen or more have been described, the plants being, even in the wild state, very variable, while the varieties in cultivation resulting from hybridizing, crossing, and sporting are innumerable. Two species are widely distributed throughout the United States, and one is peculiar to the Alpine Strawberry (Fragaria vesca). different names, as it varies greatly, and the western forms appear very different from the eastern. The Alpine strawberry (F. vesca), the common species of Europe, is indigenous to this country, especially far northward, extending to Oregon and the N. W. coast; it is found throughout Europe and northern and central Asia. It has thin pale green leaves, the upper surface strongly marked by veins; flower stalks longer than the leaves; calyx remaining open after flowering; receptacle conical or elongated, with the akenes attached to the surface, and not as in the preceding sunk in pits. A taller form is known as the wood strawberry. This was the earliest species cultivated, and is mentioned in the street cries of London of over 400 years ago; the garden of the bishop of Ely at Holborn was in 1483 celebrated for its strawberries, a fact alluded to by Shakespeare in "Richard III." A number of varieties of this are cultivated, but they are more popular in Europe than in this country. The Chilian strawberry (F. Chilensis, the F. grandiflora of some) is found on the Pacific coast from Oregon southward; it is very robust, with leathery, thick leaflets of a dark green, and sometimes silky on both surfaces, or only below; the flowers are larger than in any other species, and the large yellowish white or rose-colored fruit, sometimes as large as a small hen's egg, erect. This was introduced into the south of France in 1712, and many valuable varieties resulted until the fruit is picked, to keep it from being STREET, Alfred Billings, an American poet, born in Poughkeepsie, N. Y., Dec. 18, 1811. A lawyer by profession, in 1839 he settled in Albany, where for a number of years he was state librarian. He has published "The Burning of Schenectady, and other Poems" (1842); "Drawings and Tintings," poems (1844); collected poems (1846); "Frontenac," his longest poem (1849); "The Council of Revision," containing the vetoes of the council, a history of the courts of New York, and biographical sketches of governors and judges from 1777 to 1821 (8vo, 1860); "Woods and Waters, or the Saranacs and Racket," a description of a tour in the great northern wilderness of New York (1860); "Forest Pictures in the Adirondacks" (1864); and "The Indian Pass" (1869). STRELITZ. See MECKLENBURG. STRENGTH OF MATERIALS, the resistance offered by the materials of construction to change of form or to fracture. 1. The resistance of materials to external forces tending to overcome their cohesion is classified, according to their forms, as follows: Longitudinal. from hybridizing it with other species. The Transverse.... Tensile, resisting crushing. Bending, resisting cross breaking. Two or more of these forms of resistance are sometimes called into action simultaneously, as in the case of the crank of a steam engine, which tends to break the shaft both by a transverse strain and by torsion. 2. The "ultimate strength" is the maximum resistance offered to rupture. The "proof strength" is a less degree of resistance, which the body may safely offer when tested. The "working load" is some fractional part of the ultimate strength which may be selected as giving perfect safety against anticipated strains for an indefinite period. 3. The "factor of safety" is the ratio of the ultimate strength to the working load. The following are minimum values of this quantity adopted in what is generally considered good practice, under “dead” and "live" loads, and where the latter are liable to be accompanied by heavy shocks: Steel... Timber. MATERIAL. 4. The proof strength is usually, and should be always, below the elastic limit, i. e., the point at = P which set becomes proportional, or nearly so, Where shearing is to be resisted, the parts to the distortion produced by the applied force. should be fitted with great care, to avoid the It is generally about one half or one third the possibility of cutting, and to insure that all ultimate strength. 5. Tensile resistance, or parts of the cross section attacked shall resist tenacity, is determined by experiment for each the shearing force as nearly as possible tomaterial. The ultimate strength or breaking gether. Where a pin is fitted but not forced load of any piece is measured by the product into its socket, the resistance to shearing is of the area of fractured section into the te- taken as three fourths of that due the secnacity of the material of which it is composed; tion exposed to rupture. 9. Crushing is resisted by any given material with a force that i. e., P=TK, and K: where P represents varies very greatly with the form given it. the breaking force, T the tenacity of the ma- Very short columns or compact masses resist terial, and K the area of section. Values of very high crushing strains, in consequence of T are given in the accompanying table of co- the resistance offered by their particles to disefficients of resistance. The very best grades persion, as well as by their cohesion. Tall should have values 20 per cent. higher. P columns first bend and then break under a and T are taken in pounds upon the square comparatively slight force. The figures in colinch. 6. When thin cylinders are exposed umn C of the table give the resistance to crushto internal pressure, as in steam boilers, steaming when bending does not occur. Seasoned cylinders, &c., the bursting pressure may be determined by multiplying the thickness of the shell by the tenacity of the material, as given above, and dividing by the semi-diameter. To ascertain the thickness, the pressure and the diameter of the cylinder being given, multiply the pressure by the semi-diameter, and divide by the tenacity of the material as given in the table; or P=~, and t P = pressure, t = thickness, T = tenacity, and r = radius of the cylinder. If d = diameter, Tt Pr where P=2, and t=" Where the joints are d' 2T timber has nearly twice as great resistance to crushing as green. Steel should not be used under pressure exceeding its compressive elasticity, which, in tool steel, is about 50,000 lbs. to the square inch. Wrought iron should not be used under pressure exceeding 25,000 lbs. to the square inch. 10. For tall columns, the following formulas were proposed by Prof. Eaton Hodgkinson : MATERIALS. Solid cylindrical umns..... cal cast-iron columns.. Solid cylindrical wrought-iron columns... Solid square pil lar of Dantzic Solid square pil lar of red Rounded ends. Flat ends. W=14-9 W-13 D3-76 double-riveted, the strength at the joints is Hollow cylindri This formula is frequently designated as Gordon's, having been deduced by Gordon from beam, I, 1,000. 14. For the wrought-iron Hodgkinson's experiments. Multiply the value of a, as given in the table, by 4 for columns I beam, when supported at both ends and rounded or jointed at both ends, and by 2 where fixed at one end, rounded at the other, uniformly loaded, the formula W = D(a+*)s 12.19 Ld' Connecting rods of steam engines are calculated as pillars rounded at both ends. Piston and pump rods are considered as fixed at one end, free at the other. 11. The collapsing of boiler flues was made the subject of a series of experiments by Mr. Fairbairn, and the following formula was deduced: P-806,000 where P collapsing pressure in pounds per square inch, t thickness of iron in flues, L = length of flue in feet, and d = its diameter in inches. When the flue is strengthened by angle-iron rings, as is sometimes done with long flues, L is taken as the distance between the rings. This formula has not been verified for short flues of great diameter, or for exceptional proportions. A slight deviation from a truly cylindrical form considerably reduces the strength of the flues; t is generally taken instead of t. Elliptical flues, having a major diameter a and a minor diameter b, are of equal strength with a cylindrical flue of the diameter 2. 12. The transverse strength of beams may be calculated by the following formulas: W= W=2 Kbd2 and W KAd for beams fixed at one end and and W-2 KAd, where fixed at one end and uni- L L R 3 S' a' = .004WL3 (a+1/+) a2 ; “+ when = plied at the middle, and S': applied uniformly. The depth D is measured between the centres of gravity of the flanges. In such beams it is customary to allow as maxima 10,000 lbs. per square inch in tension and 6,000 to 8,000 in compression. Deflection should not exceed of an inch per foot of length, in any structure. 15. Torsional strength is computed by the formula W = S/D3 D= WR; ; where W = breaking weight in pounds, D = = diameter of shaft in inches, and R = length of lever arm in feet. The coefficient S' is very nearly proportional to the tenacity of the material, where the torsion is equal in degree. 16. Resilience is a term introduced by Dr. Young. It is measured by the amount of work performed in producing the maximum strain which a given body is capable of sustaining, and is the quality of primary importance where shocks are to be sustained. Mallet's coefficient of resilience is the half product of the maximum resistance into the maximum extension. for tough metals it is equal approximately to two thirds the product of the ultimate strength Here W = breaking weight in pounds, Ka of the material by the distance through which coefficient which varies with every change in the body yields before the straining force. form of cross section of the beams, d = depth half that product. No material can resist the For very brittle materials it is measured by of beam in inches, b = breadth in inches, A area of cross section of the beam at point of shock of a body in motion, unless it is capable rupture in square inches, and L = length be- of offering resilience equal to the amount of tween supports in feet. The values of K given at the given velocity; i. e., equal to the amount work performed in setting that body in motion in the table, where the beams are of rectangular section, fixed at one end and loaded at the of energy stored in the moving mass at the inother, are obtained from various sources. stant of striking. In predicting the effect of For other than rectangular sections the follow-shock, therefore, it becomes necessary to know ing may be taken as the values of K for cast the amount of energy stored in the moving body and the resilience of the resisting material. To meet a violent shock successfully, resilience, rather than mere strength, must be secured. As an instance, it is found that wrought iron of comparatively low tenacity but great toughness, capable of stretching considerably before fracture, is far superior to steel for armor for iron-clad ships; the latter has much greater strength, but also greater brittleness. Such calculations are not usually made in designing. 600; Fairbairn's riveted beam,, 900; box Immunity from the injurious effect of shock is secured by the use of a large factor of safety in proportioning parts exposed to them, by care during construction in the selection of tough resilient materials, and in management by carefully adjusting all parts, and applying the load so as to avoid jarring action as far as possible. 17. If a weight, acting as a steady load, produces a given deflection or change of dimensions, it will require but half that weight suddenly applied to produce a similar effect, whether it be fracture or a stated alteration of form. The extension of ordinary wrought iron within its limit of elasticity is about 0001 per ton per square inch of section. The amount of extension before fracture by tension is given, with the finest quality of wrought iron, at 20 per cent., with medium quality 16 per cent., and it runs in some irons as low as 4 per cent. Cast iron of fair quality is elongated but a fraction of 1 per cent. 18. The extension of steel varies with the amount of carbon, and nearly inversely as its tenacity. The following table is taken in part from Trautwine's "Engineer's Pocket Book:" ULTIMATE TENSILE STRENGTH IN POUNDS PER SQ. IN., AND ELONGATION IN INCHES, BEFORE BREAKING. NOTE.-The specimens tested were steel bars of different grades made from pure Swedish iron, and each bar was turned to a diameter of one inch for a length of 14 inches. In the larger table, the ultimate resilience of metals is given as tested in the Stevens institute of technology, Hoboken, N. J. Phosphor bronze considerably exceeds ordinary bronze in ductility and resilience. 19. Heating wrought iron within certain limits, and then cooling under stress, increases its strength by relieving internal strain. Cold rolling and wire-drawing increase it, in some cases, 100 per cent. Mr. Dean of Boston and Uchatius of Vienna have similarly increased the strength and elasticity of bronze. Overheating, annealing, and cold hammering decrease its strength. Cast iron of open structure and low density is increased in strength by successive remeltings, sometimes to the amount of 100 per cent., over pig metal. Casting under a head, or under considerable pressure, similarly benefits both cast iron and cast steel. Sir Joseph Whitworth produced a steel of extraordinary strength and toughness by casting under heavy pressure. The internal strain consequent upon sudden cooling, or upon cooling awkwardly shaped castings, seriously reduces their strength and sometimes produces actual fracture. The character of cast iron is largely determined by its density, 72 to 7-3 representing the best limits for ordinary practice. Cold wrought iron is more than twice as strong as red-hot. Strength, ductility, and resilience increase with diminishing temperatures, when the materials are of good quality. Cold-blast cast iron is usually stronger than hot-blast iron made from the same ores. Copper loses 25 per cent. of its tenacity at 550° F., 50 per cent. at 810°, and 67 per cent. at 1,000°, the, diminution of tenacity varying nearly as the square root of the third power of the temperature. Metals in large masses have usually less density and strength than when worked into sheets, bars, or wire. Wrought iron is particularly liable to loss of strength in large forgings. Bars two inches in diameter being made of the same metal as other bars one inch in diameter, the latter are sometimes found to have 20 per cent. more strength. Steel exhibits even greater differences. 20. Indentation is resisted by wrought iron nearly in proportion to its thickness. Fairbairn found the force necessary to push a blunt point or a ball 3 in. in diameter through boiler plate, one quarter of an inch thick, to be 17,000 lbs., and nearly equal to that required to drive the same instrument through a three-inch oak plank. Resistance of armor plate to penetration by shot varies, if the plate be well backed, as the square of thickness, within the limit of moderate thickness. The material should be strong and ductile. 21. Generally, in designing machines or parts of machines, they should be so proportioned that all parts will have factors of safety of nearly equal value. Economy of material is thus secured, and also the very important advantage, where exposed to severe shock or sudden strains, of utilizing the resilience of the whole machine in resisting them. Forms of uniform strength should therefore be used wherever possible. Suspension rods of uniform strength must have a greater section at the point of support than at the point of attachment of the load, as the upper portions carry not only the load but the weight of the lower part of the rod. Pump rods and wire ropes for deep mines are for this reason made tapering, with the largest section at the top. Care should always be taken that 'the pieces connected and their fastenings are, when possible, equally strong. Tall columns are slightly swollen at the middle portion in order that they may be equally liable to break at all points, and the Hodgkinson form of cast-iron beams, and the Fairbairn (I) form of section of wroughtiron beams, are given their peculiar shapes in order that no surplus material may exist in either top or bottom flange. Beams of uniform strength, when fixed at one end and loaded at the other, if of uniform depth, are triangular in plan. If uniformly loaded, they represent in plan a pair of parabolas whose vertices touch at the outer end. When of uniform breadth, their vertical sections are parabolic in the first |