548 Chronicles of Science. [Oct., 



paid particular attention to auroral plienomcna of late years, and 

 the views entertained by them receive abundant confirmation from 

 the facts observed on the dates in question. The connection be- 

 tween the aurora and magnetic storms is well known and recognized, 

 but the relation between its appearance and the phenomena of our 

 weather is not as yet nearly so universally admitted. The oppo- 

 nents of the idea of the existence of any relation, naturally and very 

 justly urge the frequency of auroras in high latitudes, without any 

 concomitant disturbance of atmospherical equilibrium. We must, 

 however, remember that magnetic intensity is in general much 

 greater in high latitudes than in our own, so that in these countries 

 it is only at times of disturbance of the magnetic confhtions of the 

 atmosphere that we are to look for an exhibition of auroral appear- 

 ances. The fact that am-oras do occur nearly simultaneously with 

 periods of stormy weather is too well estabHshed to be doubted ; the 

 point to be determined is whether there is or is not a connection 

 between the two phenomena. Some connection is distinctly assumed 

 as a fact by the authors of the papers we are noAV discussing. They 

 show that the aurora manifests itself on the appearance of a centre 

 of barometrical depression (a " bourrasque "), and that it belongs 

 to the earlier period of the disturbance, when pressure is decreasing 

 rapidly and temperature increasing, — in fact, to the period which is 

 usually characterized by the manifestation of electrical phenomena 

 such as thunderstorms. M. Silberman attributes the aurora to the 

 gradual discharge towards the higher regions of the atmosphere, of 

 the electricity contained in a thundercloud. This discharge only 

 takes place when streaks of cirri emanate from the upper surface of 

 the cloud, so that in fact it is induced by the congelation of aque- 

 ous vapour into the minute ice prisms of w^hich the cirrus is known 

 to be composed. The chief points in support of his theory, brought 

 forward by M. Silberman, are the fact that cirri are almost inva- 

 riably noticed as being present in the space above the dark segment 

 during the exhibition of an auroral discharge ; it is often remarked 

 that the phenomenon entirely disappeared w^hen the sky became 

 completely overcast with a stratum of cloud ; that durmg an auroral 

 period, in the daytime, when their luminosity cannot be observed, it 

 is frequently noticed that cirri occupy the position of the rays of 

 the aurora ; * and that frequently during an aurora a iall of small 



* Very recently a remarkable confirmation of M. Silbcrman's statements has 

 been witncss^ed by tbe writer of this Clironicle. On Ani^ust 25 he was travelling 

 from Thurso to Wick, and at .5 r.M., while the sun was shining briglitly, he observed 

 a dark bank of clouds alon,^ tlie nortiicrn horizon, exactly resciublin':; tiie dark 

 segment of an aurura. From this cloud lonij rays of cirrus directed towards the 

 zenith emanated. Although at tins period of the evening no auroral light was 

 visible, it was remarked l)y some persons who observed tlie plienomenon tliat tiiis 

 was the commencement of an aurora. During tlie night the sky, wlucli had been 

 very clear for some days previously, became entirely overcast; but before this 



