626 EEPORT— 1895. 



irregularly till four o'clock, when tlie record was only 14. After that a rise took 

 place (31 at 5 p.m. and 29 at 6 P.m.). At 7 p.m. no sensible force could be measured 

 at all. The wind, which had been blowing up the valley all day, changed in direc- 

 tion between six and seven o'clock, and was blowing down the valley when the 

 observations had to be discontinued, owing to want of light. 



The author does not draw any conclusions from these observations, but does 

 not believe that a mere dift'erence in the configuration of the ground is sutHcient to 

 account for the great differences in the electric force observed. 



6. On Iridian Thunderstorms. By C. MiciiiE Smith. 



Observation shows that the ordinary hot-weather displays of sheet lightning 

 take plsice in the region between the sea aud land breezes where there are well- 

 marked ascending currents, as shown by the great masses of pillared cumulus 

 cloud. These clouds are usually in pairs, and much of the sheet lightning consists 

 of discharges taking place between the two clouds forming such a pair. The land 

 and sea breezes difler from each other in dryness and in dustiness, and many 

 observations seem to show that thunderstorms are originated only where dry, 

 dusty, and moist, and comparatively d listless air-currents meet. This explains 

 why electrical phenomena are observed only in that part of a cyclone in which 

 the air from the sea meets the air from the laud, and why ' nor'-westers ' are 

 accompanied by such brilliant electrical displays. Dry, dusty air is usually nega- 

 tively^ electrified relatively to tlie earth, while the sea breeze is usually positively 

 electrified. The electrical displays talce place in clouds that are rapidly sinking, 

 and such clouds are ofteu surrounded by an iridescent fringe (the colours of which 

 are due probably to dust and moisture, as explained by Aitken, composed of the 

 smaller panicles left behind by the sinldng cloud). 



7. On the Zodiacal Light considered as an At^nospheric Phenomenon. 



By W. H. Wood. 



8. On the Loccd Origin of the Aurora Borecdis. By W. H. "VVooD. 



9. Report on the Application of Photography to Meteorology. 

 See Reports, p. 80. 



10. Report on the Meteorologiccd Observations on Ben Nevis. 

 See Reports, p. 186. 



MONDAY, SEPTEMBER 16. 



1. A discussion ' on the Objective Character of Combination Tones ' was intro- 

 duced by the following Paper :-r- 



Kotes on tlie Objective Existence of Combination Tones.^ 

 By A. W. RucKER, M.A., F.R.S. 



It might at first sight appear that the question of the objective existence of 

 combination tones would depend upon two others — viz. Are such notes heard .P Do 

 they exist as puUes in the air.' 



' In the following- notes the references to statements of Von Helmboltz are for 

 convenience made to the second English edition of the Sensations of Tune, translated 

 by Ellis. The references to KOnig's views are to Quelnves Ea-pericnci'S d'Acoiistiouc. 

 Paris, 1882. 



