FIRST IRON BRIDGE EVER ERECTED. Spanning river Severn in England. Completed in 1779. England, and was built in 1779. The castings were made at the Coalbrookdale Iron Works, which are still in operation. The bridge consists of one semicircular arch of 100-foot span, each of the great ribs consisting of two pieces. Robert Stephenson, the eminent engineer, said of this structure: "If we consider that the manipulation of cast iron was then completely in its infancy, a bridge of such dimensions was doubtless a bold as well as original undertaking, and the efficiency of the details is worthy of the boldness of the structure." Abraham Darby supervised the building of the bridge, and was awarded a gold medal by the Society of Arts in recognition of his work. The only previous attempt to build an iron bridge BRIDGE COMPOSED OF 3,000 CEDAR LOGS. In Pt. Defiance Park, Tacoma, Wash. ests, and, instead of building merely a wooden framework and filling it in with earth or concrete, the bridge is a solid arch of timber made up of 3,000 pieces of cedar. A Globe Tower CONEY ISLAND, the well-known seaside resort, near New York City, will have as one of its attractions a remarkable structure said to be the largest steel structure in the world-in the shape of an immense globe, the floors of last. It represents fully half a century of study, over seven years of constructive work, and an expenditure of nearly $15,000,000, and is justly regarded as one of modern times. The tunnel is about of the great engineering achievements twelve and one-half miles long, and lies at an altitude of about 2,200 feet above sea-level. It was in February of last year that the boring parties finally met at the center of the tunnel, after encountering many unexpected obstacles, the most serious of which were hot springs, and a temperature that at one time rose to 131° F., rendering continuance of the work impossible until means had been devised for cooling the atmosphere. Trains will be drawn through the tunnel by electric locomotives. The Simplon opens direct communication between Milan and Paris. PROPOSED AERIAL ROOF GARDEN. which will be devoted to various forms of amusement. This globe, which is 300 feet in diameter, will be 700 feet high, or 145 feet taller than the Washington Monument, and second in height only to the Eiffel Tower at Paris. The foundations of this remarkable structure will be of concrete encased in steel; and the superstructure will be built of steel tubes, filled with concrete, and braced with iron rods. Among its attractions will be a palm garden, 350 feet above-ground; and there will also be a weather observatory, and a wireless telegraph equipment, which, it is expected, will send communications across the Atlantic. The Simplon Tunnel THE HE famous Simplon tunnel through the Alps on the Italian-Swiss fronttier, was formally inaugurated May 19th, a decided success; and timid mortals who had been wont to declare that not for the wealth of a Wall Street oil merchant would they make the trip skyward, marveled at the gentleness of the balloon's rise when the lines were cast off the big gas-bag owned by Alfred N. Chandler of the new club. A trip in a balloon is not possible every day, except for the wealthy, for it costs about thirty-five dollars to fill the big bag with gas. The time required to inflate the balloon is about two hours. When the basket is attached, the bailoonists step in and the bags of sand are unhooked. As many men as can grasp the ropes hold the struggling balloon to earth until the aëronaut gives the word to let go. The novice expects to see the balloon shoot up to the sky like a rocket, with the passengers holding on to the ropes around the basket for dear life. Nothing could be farther from the fact. The balloon rises as gently as the blowing of the zephyr that lifts it. There is no While the mercerized cotton bag that contains the gas is being filled, bags of sand are hung around it to keep it from rising prematurely. As the big bag fills, two men are kept busy walking around the balloon, unhooking these sand bags from the ropes and attaching them to lower sections of the network. When the bag is filled with gas, the bags of sand are the only anchor that keeps the balloon from soaring heavenward. While they hold the bag, the basket in which the voyagers will stand is brought inside the ropes and attached to the bag. A fraillooking thing is this basket, but the least weight makes a difference in the lifting capacity of the balloon, and the thinnest and lightest material must be used for every purpose. swaying of the basket. The motion is almost imperceptible, and yet so fast does the machine travel that in less than two minutes it is a speck in the distance. In the ascension illustrated by the accompanying photographs, the descent was made in about two hours after the start, the balloon coming to earth under the guidance of the skilled aëronaut so gently that a glass of water could have been left on the bottom of the car without a drop being spilled. This is ballooning for pleasure. With the time for the ascension carefully chosen, and the voyage brought to a close at the right time for descending, there is little danger in the sport. The danger arises when venturesome souls try to make records or beat previous achievements. Are you worried by any question in Engineering or the Mechanic Arts? Put the question into writing and mail it to the Consulting Department, TECHNICAL WORLD MAGAZINE. We have made arrangements with the American School of Correspondence to have all such questions answered by members of its staff of Instructors. If the question asked is of general interest, the answer will be published in the magazine. If of only personal interest, the answer will be sent by mail, provided a stamped and addressed envelope is enclosed with the question. Requests for information as to where desired articles can be purchased, will also be cheerfully answered. Demagnetization of Steel Question: I have a steel rule that came in contact with a magnet. Is there any way to remove the magnetism from it without an electric coil?-J. A. M. Answer: The most satisfactory way to remove the magnetism would be, of course, by means of an electric coil through which an alternating current is passing. The magnetism could also be removed by heating the rule, but probably this would be objectionable, as it would destroy the temper of the steel. Magnetism could be removed to a very great extent by striking the rule with a wooden mallet, in order to allow the molecules of the iron to move back into the positions which they originally occupied before the rule was magnetized. Fuel Values of Wood and CoalFurnace Temperature Question 1: What is the comparative fuel value of wood and coal? Question 2: About what temperature is there in a furnace at about white heat?G. D. Answer 1: It is safe to assume about 24 lbs. of dry wood as equal to 1 lb. average quality of soft coal, and that the fuel value of the same weight of different woods is very nearly the same-that is, a pound of hickory is worth no more for fuel than a pound of pine, assuming that both are dry. It is important that wood be dry, as each 10 per cent of water or moisture in wood will detract about 12 per cent of its value as fuel. Answer 2: The temperature of a fur2,010° F. nace at white heat is approximately Increasing Voltage of Dynamos Question: I have a 50-volt 2-horse-power dynamo, and would like to increase the voltage. Is there any way it could be done by rewinding and putting on different size wire on the armature, the dynamo still running at the same speed, 2,300 per minute?-E. V. Č. Answer: The voltage is dependent upon the number of conductors in series on the armature; accordingly, you could increase the voltage by increasing this number of conductors. The increase in voltage will be directly proportional to the increase in conductors. In order that a larger number may be wound in the same space, they would have to be of smaller wire, which would decrease your current capacity, but this would be made up for by the increase in the voltage, so Pattern for Flaring Bucket Question: How is the pattern for a flaring bucket made?-A. P. Answer: The pattern for a bucket, as shown in Fig. 1, is made as follows:First draw the center line AB (Fig. 2), upon which place the height of the pail, as shown by CD. On either side of the center line, place the half-diameters CE of the top, and DF of the bottom. Then EFFE will be the elevation of the pail. Extend the lines EF until they meet the center line at B, which will be the center point with which to describe the pattern. Now, with C as center, and CE as radius, describe the semicircle EAE, and divide FIG. 2. LAYING OUT THE PATTERN. Draw a line from G to B. Starting from the point G, lay off on the arc GH the stretchout of the semicircle EAE, as shown by similar figures on GH. From H, draw a line to B, intersecting the arc IJ at J. Then GHJI will be the halfpattern for the pail, to which laps must be added for seaming and wiring, as shown by the dotted lines. FIG. 1. PERSPECTIVE VIEW OF FLARING BUCKET. Relations of Load and Brilliancy Question: It appears to me that our lights are brighter with a full load than they are with a small load. Do they get brighter with the voltage the same in both cases? If so, why?-W. I. N. Answer: It is quite possible that your lights do get brighter on full load; and if so, the explanation is that they are being supplied from a compound-wound generator which is "over-compounded," so |