lxxiv GENERAL SUMMARY OF SCIENTIFIC AND 



which the horizontal pendulum of Zollner can be used to dem- 

 onstrate Ampere's laws of the attraction and repulsion of 

 currents. 



Barker has described a new and convenient form of lecture 

 galvanometer based on the vertical lantern. Above the hor- 

 izontal condensing lens of this lantern is the upper needle, 

 suspended by a filament of silk. To this a second needle is 

 attached by means of an aluminum wire passing through 

 the condenser and the mirror. The second needle swings in 

 a coil placed beneath the inclined mirror. Any current in 

 this coil deflects the lower needle, and, of course, the upper 

 one also. This latter only appears on the screen, together 

 with the graduated scale beneath it. 



Daguenet has proposed a simple apparatus for showing 

 the phenomena of the spark in rarefied air. A barometer 

 tube a meter in length has a wire of platinum sealed in at 

 one end, and is then filled and inverted in the usual way. 

 On connecting one electrode of an induction coil with the 

 platinum, wire and the other with the mercury, the space 

 above the column is filled with a whitish light. By intro- 

 ducing air and plunging the tube in a deep cistern the spark 

 may be observed at various pressures, and by introducing 

 various other gases and liquids many beautiful effects may 

 be produced. 



Spottiswoode has presented to the Royal Society a memoir 

 giving the results of his experiments on stratification in elec- 

 trical discharges through rarefied gases. The experiments 

 were undertaken to ascertain whether the stratification ob- 

 tained with the continuous discharge of large batteries could 

 not be obtained by a less expensive arrangement in an inter- 

 rupted circuit. The various means adopted are given, and 

 the peculiarities of the discharge are described. Phenomena 

 analogous to those obtained with the coil were obtained with 

 the Holtz machine. 



Becquerel has studied the action of magnetism on the in- 

 duction spark, and shows that the loud sound which is pro- 

 duced when the current which flows around a powerful elec- 

 tro-magnet is suddenly broken between the poles is due 

 solely to the mechanical action of the magnet, the same effect 

 being produced by a strong blast of air directed on the 

 spark at the instant of breaking circuit. 



