The ideal apparatus for determining the ballast reserve would be a 

 modern electric strain-gauge. The principle of this apparatus is 

 embodied in a constantan wire fixed along a piece of steel. If the 

 steel, when under load, lengthens, the constantan wire is stretched and 

 becomes thinner and its electrical resistance increases. Constantan 

 wires would be aflixed along a part of the tub supports. The effect of 

 the thermal expansion of the steel could even be eliminated by using 

 two wires, one placed on the upper part of the lever and the other on the 

 lower part. It would then be necessary to measure the difference 

 between the two resistances. The occupants of the cabin could thus 

 always, by means of a Wheatstone's bridge, determine the weight of 

 the tubs, and therefore the ballast reserve. 



Although there are certain difficulties to be overcome, I hope to 

 have the opportunity of working out this apparatus. 



The electro-magnet which retains the lever is of conventional form : 

 it is a bell-shaped magnet with its axis vertical. Fig. 19 gives a cross- 

 section of it. One of the two poles is constituted by the central core, the 

 other by a cylinder which surrounds it. Here are the principal dimen- 

 sions of one of these magnets: diameter of core, 5-25 in.; internal 

 diameter of cylinder, 7-98 in.; external diameter, 9-6 in.; height of 

 core, 5 -44 in. The coil d is placed between these two pieces. On the 

 lower side, the magnetic circuit is closed by the base plate /J to which 

 are attached core and cylinder. The disc-shaped armature is placed 

 upon the magnet. It is upon the ring of this armature that the tractive 

 force operates. We know that if the armature touched the poles of the 

 magnet directly, a great part of the magnetic pull would persist after 

 the current was cut off. The magnet would 'stick' as they say. There 

 must then be maintained between the magnet and the armature a gap 

 called the air-space or air-gap. This air-space yields a ' demagnetizing 

 field' which demagnetizes the iron as soon as the current is cut off 

 from the coil. The weaker the coercive field of the iron, that is 

 to say, the milder it is magnetically, the more the air-space can be 

 decreased without the risk of the magnet sticking. 



Also the number of ampere-turns necessary to maintain a certain 

 magnetization in the iron is the greater the larger the air-space, since 

 it is this air-space which produces a field of demagnetization which 

 must be compensated by the field of the coil. It results from what we 

 have just said, that to economize electrical energy the iron of the 

 magnet must be as soft as possible. We were fortunate in that the Falck 



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