230 



SCIENCE. 



[Vol. XIII. No. 321 



the after deck. To these are added several rapid-fire guns of the 

 smaller calibers, placed at the most commanding positions, about 

 the vessel. . Her single military mast, in addition to the armored 

 top, carries a powerful search-light mounted on an upper platform. 



To give as great an armor protection as possible on a very 

 limited displacement, the armor has been disposed in the form of 

 an arc of a circle, turning downwards at the sides to four feet 

 below the fighting-line. The armor on the crown is three inches 

 in thickness, increasing to five inches at the sides. In order that 

 the target presented to an enemy may be as small as possible, 

 ballast-tanks have been provided capable of holding enough water 

 to lessen the cruising freeboard three feet ; so that the hull target 

 exposed, in still water, will be represented by a segment of a circle, 

 rising from zero at the water-line to four feet above at the centre 

 of the vessel. 



Particular attention has been paid to the subject of water-tight 

 compartments, and the appliances for readily freeing them from 

 water, both in case of accident and for restoring her to the normal 

 line of floatation. 



The ram bow with which this vessel is fitted, the speed that she 

 is calculated to attain, and her handiness, all combine to render 

 her a formidable and valuable addition to our seacoast defences, 

 while her coal capacity, and ability to remain at sea at a lo-knot 

 speed for over a month without recoaling, make her of the highest 

 service as a cruiser. 



Great care has been bestowed on the subject of light and ven- 

 tilation below. A complete electric plant, comprising lights, fans, 

 and blowers for ventilating, with all modern improvements, will 

 undoubtedly do away with many of the ills that prevailed aboard 

 former types of low-freeboard ironclads. 



TOBIN BRONZE. 



This alloy, manufactured by the Ansonia Brass and Copper 

 Company, New York and Chicago, is attracting attention on ac- 

 count of its high elastic limit, tensile strength, toughness, and uni- 

 form te.xture. When rolled hot, the tensile strength of the bronze 

 has been found to be greater than that of mild steel, certain tests 

 showing for the bronze an average tensile strength of 79,600 pounds 

 per square inch, and for steel 65,630 pounds ; the elastic limits be- 

 ing 54,257 pounds and 36,510 pounds respectively. 



Further, at a dead red heat, Tobin bronze can be forged and 

 stamped as readily as steel. It is maintained by those who have 

 experimented with and tested different kinds of metals with a view 

 of determining their utility for forgings, that they find Tobin bronze 

 to be the only bronze they have tried that will stand the process of 

 drop-forging. 



The alloy is lighter than copper, can be worked well in a lathe, 

 and when finished has a bright golden color. Its freedom from 

 blow-holes, durability, and anti-frictional properties adapt the bronze 

 for use on all bearing surfaces ; while its lightness, in addition to 

 its great tensile strength, and resistance to the corrosive action of 

 sea-water, renders it a suitable metal for condenser-plates, steam- 

 launch shafting, ship sheathing, etc. When rolled in sheets and 

 tempered or drawn in wire, it makes an excellent spring metal. 



Its resistance to oxidation makes it a useful material wherever 

 this is likely to occur. Some interesting experiments on this very 

 point were made with the bronze by the inspectors of machinery 

 of the United States steamers " Concord " and " Bennington." 



With a view to determining its torsional endurance for steam- 

 launch and yacht shafting, test specimens an inch long were cut at 

 random from three-fourths-inch hot rolled rods, reduced to half an 

 inch, and subjected to a torsional test in comparison with the best 

 quality of machinery steel selected by Professor J. E. Denton, pro- 

 fessor of experimental mechanics at Stevens' Institute, and tested 

 by him on Thurston's autographic testing-machine. The results 

 were as follows : average load at end of one-foot lever, which 

 strained samples to elastic limit, for bronze 328 pounds, for steel 

 340 pounds ; which ruptured samples, for bronze 633 pounds, for 

 steel 711 pounds. 



Another notable quality — its non-liability to give forth sparks — 

 makes it invaluable for gunpowder machinery and gunpowder tools 

 of every description. 



A LARGE ELECTRIC-CURRENT CONDUCTOR. 

 A NEW departure in current conductors for electric-railway pur- 

 poses has been taken by the Daft Company, who are now operat- 

 ing trains on a section of the Ninth Avenue Elevated Road in this 

 city. The new kind of conductor is shown in the accompanying 

 picture, which is a view on the road mentioned, looking south from 

 Fourteenth Street. The conductor, which is supported by heavy 

 insulated cast-iron brackets, runs along outside the outer guard-rail 

 of each track. It is of round iron, three inches in diameter, and is 

 surmounted by, and in perfect electrical contact with, a bar of 

 phospor bronze three-eighths of an inch thick by one inch wide. 

 This bar takes all the wear from the contact apparatus, and will 

 retain a polished surface under all circumstances. The supporting 

 bracket is made in two parts, as may be seen in the illustration, 

 and has a grip sufficient to prevent all possibility of displacement 



of the conductor. The conductor is elevated a considerable dis- 

 tance from the ties, and the sup'porting brackets are well insulated, 

 so that the chances of loss of electric energy through leakage are 

 reduced to a minimum. 



The difference in cost of iron and copper admits of the greatly 

 increased size of conductor, giving the same conductivity at much 

 less expense. 



The Daft Company are now equipping the Ninth Avenue road 

 with this conductor from Fourteenth Street south to Rector Street 

 station, near the Battery ; the success attending the running of 

 their trains north from Fourteenth Street during the past winter 

 encouraging them to extend operations and equip a greater length 

 of track as rapidly as possible. 



A METEOROLOGICAL EXHIBITION. 



Several months since, the New England Meteorological So- 

 ciety, following the annual custom of the Royal Meteorological 

 Society of London, decided to hold a loan exhibition in Boston in 

 connection with its fourteenth regular meeting. The exhibition 

 was opened in the physical laboratory of the Massachusetts Insti- 

 tute of Technology, Jan. 15, and was continued seven days. 

 Among those who sent apparatus were Mr. Rotch from his Blue 



