Scientific American Supplement, No. 821 | Page 2

a dial surmounted by a shield bearing the device of the city of Paris.
The central door of the ground floor opens upon a large vestibule, around which are arranged symmetrically the post, telegraph, telephone, and intelligence offices, etc. Beyond the vestibule there is a gallery that leads to the central court, upon the site of which has been erected the grand assembly hall. This latter, which measures 20 meters in length, 22 in width, and 6 in height, is lighted by a glazed ceiling, and contains ten rows of benches. These latter contain 900 seats, arranged in the form of circular steps, radiating around the president's platform, which is one meter in height. A special combination will permit of increasing the number of seats reserved for the labor associations on occasions of grand reunions to 1,200. The oak doors forming the lateral bays of the hall will open upon the two large assembly rooms and the three waiting rooms constructed around the faces of the large hall. In the assembly rooms forming one with the central hall will take place the deliberations of the syndic chambers. The walls of the hall will, ere long, receive decorative paintings.--_L'Illustration._
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MANUFACTURE OF ROLL TAR PAPER.
Roofing paper was first used in Scandinavia early as the last century, the invention being accredited to Faxa, an official of the Swedish Admiralty. The first tar and gravel roofs in Sweden were very defective. The impregnation of the paper with a water-proofing liquid had not been thought of, and the roofs were constructed by laying over the rafters a boarding, upon which the unsaturated paper, the sides of which lapped over the other, was fastened with short tacks. The surface of the paper was next coated with heated pine tar to make it waterproof. The thin layer of tar was soon destroyed by the weather, so that the paper, swelled by the absorption of rain water, lost its cohesiveness and was soon destroyed by the elements. This imperfect method of roof covering found no great favor and was but seldom employed.
In Germany the architect Gilly was first to become interested in tar paper roofing, and recommended it in his architecture for the country. Nevertheless the new style of roof covering was but little employed, and was finally abandoned during the first year of the 19th century. It was revived again in 1840, when people began to take a renewed interest in tar paper roofs, the method of manufacturing an impermeable paper being already so far perfected that the squares of paper were dipped in tar until thoroughly saturated. The roof constructed of these waterproof paper sheets proved itself to be a durable covering, being unimpenetrable to atmospheric precipitations, and soon several factories commenced manufacturing the paper. The product was improved continually and its method of manufacture perfected. The good qualities of tar paper roofs being recognized by the public, they were gradually adopted. The costly pine tar was soon replaced by the cheaper coal tar. Square sheets of paper were made at first; they were dipped sufficiently long in ordinary heated coal tar, until perfectly saturated. The excess of tar was then permitted to drip off, and the sheets were dried in the air. The improvement of passing them through rollers to get rid of the surplus tar was reserved for a future time, when an enterprising manufacturer commenced to make endless tar paper in place of sheets. Special apparatus were constructed to impregnate these rolls with tar; they were imperfect at first, but gradually improved to a high degree. Much progress was also made in the construction of the roofs, and several methods of covering were devised. The defects caused by the old method of nailing the tar paper direct upon the roof boarding were corrected; the consequence of this method was that the paper was apt to tear, caused by the unequal expansion of the roofing boards and paper, and this soon led to the idea of making the latter independent of the former by nailing the sides of the paper upon strips running parallel with the gable. The use of endless tar paper proved to be an essential advantage, because the number of seams as well as places where it had to be nailed to the roof boarding was largely decreased. The manufacture of tar paper has remained at about the same stage and no essential improvements have been made up to the present. As partial improvement may be mentioned the preparation of tar, especially since the introduction of the tar distillery, and the manufacture of special roof lacquers, which have been used for coating in place of the coal tar. As an essential progress in the tar paper roofing may be mentioned the invention of the double tar paper roof, and