Proceedings of the British Association. 371 
exception of one solitary instance, the station being in the Pyrenees 
and in the neighborhood of iron mines, there was no diminution of 
the magnetic intensity at the higher stations, at least beyond the 
limits of the necessary errors of instruments and observations ; even 
at the station where some diminution did manifest itself, the quantity 
of that diminution was very much smaller than that which resulted 
from the views of M. Kuppfer. 
Prof. Powell read a paper “respecting the impermeability of 
water to radiant heat.” 
A paper by Sir David Brewster, ‘‘ On the action of crystallized 
substances upon Light,” was then read by the Secretary, Mr. Snow 
Harris. 
Dr. Williams gave an account of an improved ear trumpet. 
The President then said, that as there were yet a great many in- 
teresting communications to be brought forward, the Section would 
reassemble at eight o’clock in the evening. 
Thursday Evening.—Mr. G. W. Hall made a communication 
upon “the connexion observed at Bristol] between the weather and 
the tide.” He commenced by stating, that long and carefully con- 
tinued observation of the weather at Bristol, together with a direct 
interest in becoming possessed of rules for anticipating its changes, 
Jed to the following theory, which was strikingly correspondent with 
facts. First, that the barometer very generally, indeed, almost in- 
variably, undulates at times corresponding with the changes of the 
moon, and at these times it more frequently falls than rises. Sec- 
ondly, that the weather is ordinarily unsettled at these periods, con- 
tinuing so for about two or three days; and for the most part the 
wind becomes high at these times. Thirdly, that as the weather 
settles (if it become at all settled, since it not unfrequently remains 
in an unsettled state,) so will it continue until the next change of 
moon, or rather until the recurrence of its disturbing influences. 
ppt that these variations occur-as regularly at the quarters of 
the moon as at the new and full, and are then as fully marked. 
Fifihly, that the period, about five days, which determines the state 
of the weather, is derived from the spring and neap tides, or the full 
influence of the sun and moon upon them.—The only origin of these 
rules, he stated, was actual observation. Very striking changes of 
temperature and weather, from intense frost to spring mildness, and 
then frost recurring, first led to marking this correspondence ; and 
so closely has it been observed, and so fully established, that opera- 
