Proceedings, &c. } for 1884. 159 



Piazzi Smith was of opinion that some years must elapse before it 

 would be possible to arrive at any definite conclusion, and he sug- 

 gested a more careful analysis of the constitution of the very high 

 strata of the atmosphere than had hitherto been made. Of the 

 theories put forward, certainly three of them required for their 

 complete establishment the removal of the one difficulty which 

 had been raised by Mr. Ellery as to the precipitation of the dust. 

 Some very curious theories had been started to account for the 

 suspension in the atmosphere of meteoric or volcanic dust. Preece 

 was said to have suggested that the particles were similarly 

 electrified, so that by mutual repulsion they were maintained at a 

 high altitude. Professor Andrew then proceeded to prove from 

 dynamical principles that the suspension in the atmosphere, for 

 long periods, of particles of dust specifically heavier than the air 

 was not incompatible with known dynamical laws. 



The President said that there were instances of the extra- 

 ordinary afterglow and of a green sun noticed prior to the 

 Krakatoa eruption, and he reminded the members of the Society 

 of the great aurora of 1869, when at 10 o'clock on a moonless 

 night one could read the newspaper by the red light of the 

 aurora, which was far more intense than even the recent remark- 

 able sunsets. He did not think the volcanic dust found in Spain 

 and Holland proved anything more than that it had probably 

 been thrown up into the air by the explosion at Krakatoa, and 

 had fallen in the countries named. But that did not, in his 

 opinion, account for the peculiar sunsets. The theory that we 

 were passing through a region of cosmic dust was equally possible, 

 but very improbable, considering, from the time the afterglows 

 have continued, that we must have passed through a belt 

 180,000,000 miles in thickness, and are still in it, the sunset 

 that evening being as beautiful as any we have had. He believed 

 it would yet be found that water, in some form, had played the 

 principal part in the sunsets. He had had another idea, but it 

 was more of a speculation than a theory. At the time of the 

 Krakatoa earthquake there was noticed all round the world a 

 peculiar disturbance of all the barometers, repeated at certain 

 intervals for several days after the explosion, and he could 

 imagine that a terrific blow by the lower to the more elastic 

 portion of the upper atmosphere had given a kind of shudder 

 round the earth, disturbing the whole region of the upper atmo- 

 sphere, the upper air having a kind of shiver, so to speak. If it 

 were admitted that such a thing was possible — and they must 

 admit also, as chemists, that there are states of matters, com- 

 pounds and mixtures, combinations, and so forth, where they are 

 in a state of equilibrium, just on the verge of combining or 

 breaking up — a shock like that would cause a total alteration of 

 the physical character of the mixture or matter on which it was 



