Stratified Discharges. 233 



the conductors of the machine and by increasing the number of 

 the jars. 



The first object proposed was to ascertain whether a jar could 

 be charged with so small a quantity of electricity as of itself 

 to give a stratified discharge in a tube ; in other words, whether 

 the resistance of the tube itself, if resistance it be, could by a 

 suitable charge of jar be made to insure a stratified discharge. 

 For this purpose a jar was charged with small sparks from the 

 machine, and discharged after receiving charges of 1, 2, 3, &c. 

 sparks in succession. The experiment proved successful with a 

 coal-gas tube at a pressure of about 4 millims. : charges of three 

 sparks gave bright flake-like stratifications ; higher charges gave a 

 discharge with a positive column, a negative glow, and a dark space, 

 although the striae were not always discernible. But when the 

 charge exceeded 5 or 6 sparks, the positive column advanced so 

 far as to obliterate the dark space, and ultimately made its way to 

 the hilt of the terminal. 



Similar experiments were made with both forms of instru- 

 mental arrangement, and with tubes containing different gases and 

 at different pressures. 



A number of tubes tried with various amounts of battery-charge, 

 but with the same surface, showed that, as the charge was increased, 

 the head of the positive column advanced towards the negative ter- 

 minal, the dark space became narrower, and the glow contracted 

 in dimensions ; and when the head of the column drew very near 

 to the negative terminal, the glow, instead of covering the whole 

 surface of the terminal, formed a small drop at the point. On 

 still further increasing the charge, the drop withdrew to the hilt 

 of the terminal ; and finally, when it had completely retreated into 

 the hilt, the continuous or true jar-discharge took place. 



With a view to testing experimentally how far the effects here 

 described were due to quantity and how far to tension, the size of 

 the jar was altered, all other circumstances remaining the same. 

 It was then found not only, as before, that small charges gave 

 stratified and large unstratified discharges, but also that the 

 maximum charge compatible with stratification was greater with a 

 large than with a small jar. 



As a further experiment in this direction, a series of jars were 

 arranged in cascade ; and it w^as found that the greater the num- 

 ber of jars so arranged, the smaller the charge necessary to insure 

 a true jar-discharge. A charge insufficient to destroy stratification 

 with one jar was sufficient to destroy them when more than one 

 was used in cascade. These results point to tension rather than 

 to quantity as the determining cause of the character of the dis- 

 charge. 



In fact, having taken a number of jars of the same size, and 

 having ascertained the maximum charge with which one jar could 

 be charged without obliterating stratification, say, " the critical 

 charge," I found that the critical charge for 2, 3, . . . jars arranged 

 for quantity was 2, 3, . . . times that for a single jar ; and, on 

 the other hand, that the critical charge for 2, 3 . . . jars arranged 



