24 Mr. C. Tomlinson on the Action of Solid Nuclei. [May 8, 



it can be made to return into its own terminal, while the other takes 

 no part in the discharge ; or, finally, the two terminals can be made 

 to ponr out independent discharges of the same name, each of which 

 returns to its own terminal. 



Having traced the relation between the two parts of the dis- 

 charge, and having found means for controlling their range and 

 influence, the authors were led to inquire whether there be any 

 experimental evidence of the state of the tube during the occurrence 

 of the discharge. Some experiments with two pieces of tinfoil of 

 unequal size placed near the ends of the tube and metallically con- 

 nected ; and others with a strip of tinfoil placed along the tube, all 

 gave effects showing that the discharge cannot be simultaneous 

 throughout the tube. The phenomena appear to require for their 

 interpretation that, in front of the pulse coming from the (positive) 

 air-spark terminal, there is, during the interval between the pulses, a 

 rising negative potential. This is entirely swept out by the pulse as 

 it advances along the tube ; after which the process is repeated. The 

 condition of things behind the pulse is more difficult to determine ; 

 but an experiment with the telephone gives reason to think that parts 

 of the tube nearer to the non-air-spark end are in a condition to 

 demand relief, before those nearer to the air-spark terminal have 

 ceased to require it. And on this account the discharge may, perhaps, 

 be more nearly represented by a lazy tongs than by a bullet. 



How far the results obtained from the sensitive state are applicable 

 to ordinary discharges is a question which cannot yet be definitively 

 answered. But the marked similarities in the phenomena, and the 

 predisposing circumstances of striation or non-striation, as well as in 

 the terminal peculiarities of the two kinds of discharge, point strongly 

 to the conclusions that all vacuum discharges are disruptive ; and that 

 sensitive differ from non-sensitive discharges mainly in the scale of the 

 discontinuity due to the disruptiveness, causing a difference between 

 the two classes of phenomena analogous to that between impulsive 

 and continuous forces in dynamics. 



II. " On the Action of Solid Nuclei." By Charles Tomlinson; 

 F.R.S. Received April 22, 1879. 



It is stated in my second paper on supersaturated saline solutions 

 ("Phil. Trans.," 1870, p. 53), that among nuclear bodies "are per- 

 manently porous substances, such as charcoal, coke, pumice, meer- 

 schaum," also that " certain liquids act as nuclei by separating 

 water instead of salt from supersaturated solutions. Absolute alcohol 

 acts in this way." 



