July 26, 1889.] 



SCIENCE. 



55 



ARNOLD'S RETARDATION INDICATOR. 



The retardation indicator siiown in the accompanying engraving 

 is an apparatus intended to be placed in ttie cab of a locomotive, 

 for indicating the relative measure of resistance exerted by the air- 

 brakes when arresting the momentum of the train. By its use the 

 person operating the brakes may be enabled to so regulate the 

 steam or air pressure applied to the brakes as to prevent a too rapid 

 stoppage of the train, and the consequent discomfort to the passen- 

 gers. 



The indicator consists of a tube, with upturned ends, arranged 

 horizontally in the cab or car, the axis of the tube being parallel 

 with the direction in which the train is to move. This tube con- 

 tains mercury, which, as the train starts or stops, shows a differ- 

 ence of level in the upturned ends of the tube, governed by the 

 rapidity of the starting or stopping, the change of momentum be- 

 ing proportional to the impulse producing it. Each end of the tube 

 is provided with a freely moving piston, which rests upon the sur- 

 face of the mercury. These pistons are attached to an arm which 

 is pivoted in the centre, the pistons exactly balancing each other. 

 Attached to an extension of this arm is a bevel-geared sector, which 

 meshes into a pinion connected with the pointer on the dial-plate. 

 When the train is at rest, or moving at uniform speed, the pointer 

 remains at zero on the dial ; but, when starting up or slowing 



of these vessels and ducts combined with the wood-cells in any 

 stem to render the structure exceedingly heterogeneous. Most of 

 these cells and vessels have their longer diameter parallel with the 

 general direction of the stem. Groups of thin-walled, prismatic 

 cells pass radially from the central portion of the stem to the cir- 

 cumference. These groups of cells are called medullary rays. It 

 is impossible to cut a filament from any of these woods so that the 

 medullary rays will not cross it many times at right angles to the 

 ducts and long cells. The character of the cells forming these 

 rays is so very different from the others in the filament, as to shape, 

 direction, and thickness of the walls, that at the crossing points 

 resistance is greatly increased, thus causing rapid burning and de- 

 struction at such points. 



Such woods as hickory and rock-elm furnish the very best of our 

 timbers. They are the toughest and most durable of our woods, 

 but they do not make good filaments. The medullary rays are 

 very numerous, and the walls of the cells composing them are 

 greatly thickened. The long, pointed, thick-walled wood-cells do 

 not follow a parallel course, but interlace with each other. This 

 interlacing of the cells gives to these woods their toughness. It is 

 the main characteristic, also, which renders them worthless when 

 made into electric filaments. Upon carbonization of such filaments, 

 the tension of the interlacing cells is relieved, and the tissues com- 

 posing it become friable, and easily fall apart. 



ARNOLD'S RETARDATION INDICATOR, 



down, the pointer moves around the dial, to the right or the left, a 

 distance proportional to the rapidity of the starting or the stop- 

 ping. 



Among the advantages claimed for it are the following : it shows 

 the engineer at any instant the effect of the brakes upon the wheels, 

 and enables him to retard the train uniformly, regardless of the 

 condition of the track or of the air-pressure ; it economizes the air, 

 and prevents an undue shock or strain on the brake-rigging or the 

 car-body ; and it enables the engineer to apply the brakes gradu- 

 ally, and with increasing effect, until the train is brought to rest. 

 The indicator is manufactured by J. H. Reynolds of Troy, N.Y. 



ELECTRICAL NEWS. 



Incandescent Electric Lamp Filaments. 



In a recent communication to the Academy of Natural Sciences 

 of Philadelphia, on the use of bamboo in incandescent electric 

 lighting. Professor William P. Wilson states, that, for want of a 

 homogeneous structure, the ordinary exogenous woods are not 

 adapted to the construction of lamp-filaments. Such woods are 

 made up of wood-cells of varying lengths and shapes in combina- 

 tion with a variety of ducts and vessels. 



The walls of the wood-cells may be more or less thickened, the 

 vessels and ducts may be larger or smaller, numerous or infrequent, 

 according to the kind of wood examined. There are always enough 



In the adult stem of the bamboo a combination of anatomical 

 characters has brought about a result which makes it the most 

 fitting material, so far as now known, for the electric filament. The 

 nearly parallel fibro-vascular bundles grow more numerous as they 

 approach the circumference of the stem, and, as is usual in similar 

 stems, lose most, or sometimes all, of the woody elements, thus 

 becoming pure bast. The parenchymatic tissue, which toward the 

 centre of the stem may be composed of a layer of five or six cells 

 between the bundles, decreases in amount near the circumference 

 until but one layer of cells remains. The walls of the cells 

 in this single laver often become so thickened, and at the same 

 time compressed by the growth of the bast, that these bundles 

 appear to make a solid zone of bast around the circumference of the 

 stem. The bast-cells also continue to thicken their walls until 

 they become, in the best specimens for the filament, completely 

 filled and solid. It is from this zone of bast at the circumference 

 of the stem that the filament is always taken. It is perhaps the 

 nearest approach, in its continuity of structure and uniform char- 

 acter, to a metallic conductor, of any tissue which can be found in 

 the vegetable kingdom. 



Photographs of Lightning. 



At a meeting of the Physical Society of London held June 22, 

 and reported in A^a/ure, Mr. A. W. Clayden presented a note on 

 some photographs of lightning, and of " black " electric sparks. 

 The lightning photographs, three in number, were obtained dur- 



