1892.] on Alternate Currents of High Potential and Frequency. 647 



less a lightning discharge is to afford it in some way a passage through 

 a volume of gas. 



The recognition of some of the above facts has a bearing upon far- 

 reaching scientific investigations in which extremely high frequencies 

 and potentials are used. In such cases the air is an important factor 

 to be considered. So, for instance, if two wires are attached to the 

 terminals of the coil, and streamers issue from them, there is dissi- 

 pation of energy in the form of heat and light, and the wires behave 

 like a condenser of larger capacity. If the wires be immersed in oil, 

 the dissipation of energy is prevented, or at least reduced, and the 

 apparent capacity is diminished. The action of the air would seem 

 to make it very difficult to tell, from the measured or computed 

 capacity of a condenser in which the air is acted upon, its actual 

 capacity or vibration period, especially if the condenser is of very 

 small surface and is charged to a very high potential. As many 

 important results are dependent upon the correctness of the estimation 

 of the vibration period, this subject demands the most careful scrutiny 

 of other investigators. 



In Leyden jars the loss due to the presence of air is comparatively 

 small, principally on account of the great surface of the coatings and 

 the small external action, but if there are streamers on the top, the 

 loss may be considerable, and the period of vibration is affected. In 

 a resonator, the density is small, but the frequency is extreme, and 

 may introduce a considerable error. It appears certain, at any rate, 

 that the periods of vibration of a charged body in a gaseous and in 

 a continuous medium, such as oil, are different, on account of the 

 action of the former, as explained. 



Another fact recognised, which is of some consequence, is, that in 

 similar investigations the general considerations of static screening 

 are not applicable when a gaseous medium is present. This is 

 evident from the following experiment. 



A short and wide glass tube is taken and covered with a substantial 

 coating of bronze, barely allowing the light to shine a little through. 

 The tube is highly exhausted and suspended on a metallic clasp from 

 the end of a wire. When the wire is connected with one of the 

 terminals of the coil, the gas inside of the tube is lighted in spite 

 of the metal coating. Here the metal evidently does not screen the 

 gas inside as it ought to, even if it be very thin and poorly conducting. 

 Yet, in a condition of rest the metal coating, however thin, screens 

 the inside perfectly. 



One of the most interesting results arrived at in pursuing these 

 experiments, is the demonstration of the fact that a gaseous medium, 

 upon which vibration is impressed by rapid changes of electrostatic 

 potential, is rigid. In illustration of this result an experiment may 

 be cited. 



A glass tube about 1 inch in diameter and 3 feet long, with out- 

 side condenser coatings on the ends, was exhausted to a certain point, 

 when, the tube being suspended freely from a wire connecting the 



