On Stratifications and Dark Bands in Electrical Discharges. 307 



peai'ance of discharge from the induction-machine can in no way 

 arise from the emanation of particles of the metal. 



The author describes a series of experiments made in the apparatus 

 first prepared, by which the mercury is lowered or raised in the 

 vacuum tube ; he describes the peculiar appearance when the mer- 

 cury is made either positive or negative. In some instances, and 

 particularly when, instead of wires, platinum balls ^tli of an inch in 

 diameter were used for terminals, the stratifications instantly ceased 

 when the mercury rose above the negative ball; but when the pole 

 of a magnet was presented to the positive ball, the stratifications 

 were drawn to the length of two or three inches down the tube. 



In the sealed tubes the stratified discharge was obtained by fric- 

 tional electricity ; and if a charged Lej^den jar is discharged through 

 the vacuum by a wet string, the stratifications are as distinct as from 

 the induction-coil. 



The author next proceeds to show, that hy a single disruptive dis- 

 charge of the primary current excited by a single cell, the entire 

 tube, whatever may be its length, is filled with stratifications as far 

 as the dark band near the negative wire ; and from this experiment 

 he is of opinion that the phenomenon cannot be in any way due to 

 the vibrations of the contact-breaker. With one, two or three cells 

 no appearance of a luminous discharge could be perceived on making 

 contact, it only appeared on breaking. If, however, the intensity of 

 the primary current is increased by using ten or more cells, stratifi- 

 cations appear on making as well as on breaking the contact of the 

 primary circuit. These stratifications are always concave towards 

 the positive terminal, and as the discharges, on making and on break- 

 ing, emanate from different terminals, their concavities are in oppo- 

 site directions, — a fact which explains the different ways in which 

 several electricians have described and figured the form of the dis- 

 charge with the coil. These stratifications appear in quick succession, 

 but they can always be sej)arated in any part of the tube by a magnet. 



Under certain conditions the positive discharge assumes a peculiar 

 form, of which the author gives a drawing. He considers that this 

 exhibits a direction of a force from the positive to the negative, cen- 

 tering to the axis of stratification, which cannot be connected with 

 the passage of particles, and that the latter phenomenon, as it occurs 

 in the voltaic arc, may be but the result of a secondary action. 



The author notices the peculiar difference between the positive 

 and negative discharge ; he describes an apparatus by which both 

 terminals could be made of surfaces of mercury, or the positive of a 

 surface of mercury, and the negative of a wire, or the reverse. In 

 this apparatus, moreover, the mercury at one end could be elongated 

 y or 10 inches. When the mercury was negative, its entire surface 

 was covered with a brilliant glow ; when positive, the extreme point 

 of the mercury exhibited intense light, but the remainder of the sur- 

 face appeared unaifected by the discharge. In order to test whether 

 any signs of interference could be detected, he had a tube prepared 

 with four wires, by which discharges could be observed when taken 

 from separate coils, as siiown in fig. 2, where a b and a! V are 

 platinum wires hermetically sealed, as in the previously described 

 apparatus. Care was taken to manipulate with induction-coils givhig 



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