ON PHOTOGRAPHY OF METEOROLOaiCAL PHENOMENA. 139 



sparks being jjossibly determined by the difference of potential required 

 to break through what resistance there was. 



Possibly it may be found that the ribbon structure is also due 

 to some such phenomenon. The passage of the first flash will produce 

 for a short time a Lighly rarefied column of air, through which a stream 

 of less luminous sparks may pass until the displaced air surges back. 

 Resistance will then be abnormally high exactly along the track of the 

 first spark, and this column of extra dense air will be surrounded by a 

 tube (so to say) of lower resistance. Indeed, the paths of subsequent 

 discharges in a series may conceivably be determined either by the 

 outward movement of the wave of rarefaction or by the alternate com- 

 pression and rarefaction along the original path. In either case the 

 movement of the air may easily sufiBce to carry the position of least 

 resistance along with it. That subsequent discharges do sometimes 

 follow what may be called the trough of the atmospheric wave is indi- 

 cated by the tendency sometimes exhibited for one spark or flash to 

 twist partly round another. 



Howevei', your committee do not wish it to be understood that they 

 put forward these suggestions as definite hypotheses. They merely state 

 them in order to indicate various lines along which further research is 

 desirable. They hope, if they are permitted to continue their task for 

 another je&v, to add considerably to the experimental and observational 

 facts at present available, and possibly to reach more definite conclusions 

 than existing material allows. 



Before ending their report your committee feel that a passing 

 reference is due to the important paper read before the Royal Society in 

 which the Kev/ Committee described some of their results, and also to 

 the work which has been carried on at Berlin and elsewhere in the 

 photography of the so-called luminous night-clouds and of clouds in- 

 visible to the naked eye. 



They wish to express their thanks to the Kew Committee, to the 

 numerous i^ersons who have volunteered their assistance, and especially 

 to the Council of the Royal Meteorological Society, 



In conclusion they ask to be reappointed, with a grant of 15^., in 

 order that they may have an opportunity of following up the beginning 

 that has been made. 



Report of the Committee, consisting of Professor 0. J. Lodge, 

 Professor Carey Fosteh, and Mr. A. P. Chattock (Secretary), 

 appointed to investigate the Discharge of Electricity from 

 Points. 



Measueejiekts have been made of the strength of field necessary to start 

 discharge at jjoints of radius of curvature varying from 0'7xlO"^ to 

 58 xlO"^ cm. The I'esults show that the field strength inci'eases rapidly 

 as the radius of curvature diminishes. They also point to the gas sur- 

 rounding the point as the seat of resistance to discharge, rather than to 

 the surface of the metal ; and, upon the assumption that discharge means 

 the breaking down of Grotthuss chains in the gas, extrapolation indicates 

 an atomic charge of dimensions approximating to those of the ionic 

 charge of electrolytic ions. 



