274 



ELECTEIOITY. 



is read in the same manner as the ordinary cup 

 and dial anemometer, or as a gas-meter. By 

 means of the formula before mentioned (al- 

 though the unit of measurement in this instru- 

 ment is five-hundredths) the observer may 

 arrive at results as near the truth as if the in- 

 strument were capable of registering the one- 

 thousandth part of a mile, while the great 

 advantage lies in the fact that the battery- 

 power is less called into action, from which 

 we may infer its elemental duration will be 

 considerably longer. 



A Magnetic Paradox. Such is the term ap- 

 plied by S. Alfred Varley to an instrument 

 exhibiting the phenomenon of the apparent 

 repulsion of soft iron by a magnet. 



The apparatus consisted of a compound magnet iu 

 a box, and when pieces of soft iron were placed on 

 the box over the poles they became magnetic by in- 

 duction and were attracted by the magnet ; but, if a 

 soft-iron bar, not by itself magnetic, was approached 

 near to the pieces of iron, they leaped away from the 

 magnet in tne box and became strongly attached to 

 the soft-iron bar, the pieces of iron appearing to be 

 repelled by the magnet and attracted by the iron bar. 

 The author stated the explanation demonstrated the 

 duality of the magnetic force, and it would also prove, 

 did we not already know it, that magnetic force was 

 transmitted only by induction. He stated that if a 

 piece of soft iron were placed over the poles of a 

 magnet, the magnet develops the magnetic forces 

 resident in the iron by separating them, and the iron 

 is attracted only by virtue of the forces existing in 

 the iron itself, and to the extent to which the forces 

 are separated. If the magnet be bent, bringing the 

 lower pole round and over the piece of soft iron, the 

 magnetic forces resident in the soft iron will be more 

 developed ; but if the piece of soft iron be midway, 

 it will not be attracted, as the forces on either side 

 are equal and balance ; another attraction will, how- 

 ever, be manifested if one pole be nearer to the piece 

 of iron than the other. If, instead of bending the 

 magnet as just described, the piece of soft iron placed 

 over the magnet be approached by a soft-iron bar, 

 the magnetic forces separated and rendered active in 

 the piece of iron will develop the magnetic forces 

 resident in the iron bar, and, if the bar opposed no 

 resistance to the assumption of the magnetic condi- 

 tion, it would exert an attractive force for the piece 

 of soft iron equal to that exerted by the magnet, pro- 

 vided always that the bar was at the same distance. 

 It was stated that as the mass of iron in the iron bar was 

 much greater than that of the piece of soft iron, the 

 resistance opposed by the bar to polarization was 

 comparatively small, and might be disregarded, and 

 consequently it followed that as the dual forces resi- 

 dent in iron are equal, and the one force cannot be 

 developed without equally developing the other; 

 when the iron bar was approached nearer to the piece 

 of soft iron it became attracted, leaping away from 

 the magnet and attaching itself to the iron bar, and 

 this notwithstanding that the attractive force exhib- 

 ited by the iron bar has been called into being by the 

 magnet in the box, which is nearer to the piece of 

 soft iron than it is to the iron bar. The iron bar also 

 collected the magnetic rays of force issuing from the 

 magnets, and consequently it exerted a greater at- 

 traction for the piece of soft iron than any individual 

 magnet forming part of the compound magnet. This 

 was shown by placing a piece ot soft iron on the pole 

 qf one of the magnets and removing it from the pole 

 by the superior attractive force of the iron bar. It 

 was also shown that, if only the thickness of a piece 

 of writing-paper were placed between the magnets 

 and the piece of soft iron, the appearance of repulsion 

 could be prevented. 



Nairn's Electrical MacJiine. This machine 

 has been modified and improved by suspending 

 a Leyden jar from each of the conductors, and 

 connecting the outer coatings of the two jars 

 by a chain. The permanent and complete 

 neutralization of the coatings thus united gives 

 great energy to the condensation. By em- 

 ploying jars 160 millimetres high and 90 in 

 diameter, M. Perard has succeeded in piercing 

 a plate of glass 6 millimetres thick, although 

 the glass cylinder of the machine was only 50 

 millimetres in diameter, and the cushion 380 

 long. With this arrangement sparks 100 mil- 

 limetres long can be obtained ordinarily, and 

 even 170 when the atmospheric conditions 

 favor. The spark, however, has not the inten- 

 sity of that of Holtz's machine or Kuhmkorff's 

 coil, but is much more powerful than the first, 

 and may be compared to that of a large coil 

 for amplitude and brilliancy. The detonation 

 of the longest spark is as loud as that of the 

 spontaneous discharge of a battery of six Ley- 

 den jars. 



The Neio TJiermo- Electric Pile. Further 

 experiments with the new pile contrived by 

 Messrs. Mure and Clamard seem to demon- 

 strate its economic value. Forty couples, act- 

 ing for ten consecutive hours, consumed 785 

 litres of gas at an expense of 2J centimes an 

 hour. From this pile visible sparks were ob- 

 tained between the two electrodes; the current 

 reddened a platinum wire 0.3 millimetres in 

 diameter and 35 millimetres long, and also de- 

 composed water. The electro-motive force of 

 40 couples is equal to that of a Bunsen element. 

 Le Genie Industricl gives the following de- 

 tailed account of the structure of the improved 

 pile: 



It is made up of 60 elements. These consist of small 

 bars of lead, or native sulphuret of lead, and of plates 

 of steel. The bars are 40 millimetres long by 8 thick, 

 and the plates of steel are 55 millimetres long by 8 

 broad, and 0.6 thick. 



In these couples galena is the electro - negative 

 element ; iron, the electro-positive. The form of the 

 bars is such that, by placing them side by side, they 

 make a ring of 12 couples, of which the interior is 

 formed by the extremities which are to be heated. 

 They are united in tension by means of tin solder. 

 They are isolated from one another by thin mica 

 plates. By placing 5 of these rings in a vertical 

 column, a battery of 60 couples is formed. These 

 rings are isolated and separated by washers of as- 

 bestos. The whole is firmly held between 2 iron 

 rings by means of 3 bolts. 



The pile thus forms a hollow cylinder, the interior 

 of which must be heated. The cooling of the junc- 

 tions, whose temperature should be lower, is caused 

 by radiation into the air. The interior cylinder 

 measures 50 millimetres in diameter and about the 

 same in height. The heated surface is about 78 sq. 

 centimetres. The apparatus is heated by a gas- 

 burner, consisting of a steel cylinder 56 millimetres in 

 diameter, closed above, open below, and pierced with 

 small orifices. This is placed in the centre of the 

 pile. A tube pierced with holes surrounds this 

 cylinder and distributes the gas uniformly around 

 it. The gas rises, and, arriving at the orifices in the 

 burner, meets the air which is escaping from it be- 

 cause of the draft of the tube of steel that surrounds 

 the apparatus. Each orifice in the burner thus forms 

 a blow-pipe, the jet of which strikes the oppsite side. 



