Meetings of the Scientific Association of Great Britain. 63 
jum in the plane of the magnetic meridian, and perpertinalaly to 
this plane, do not give the same values. 
I cannot forbear mentioning a fact sufficiently curious, ohio I ob- 
served in London at Mr. Watkins, and which Mr. Christie has con- 
firmed by his own experiments; it is that pieces of very soft iron, 
’ after having acquired magnetism by induction, preserved all their 
force during a fortnight, and others even a month, after being sub- 
jected to a current of electricity, but when separated from the ar- 
mature, their power almost entirely disappeared. JI had an oppor- 
tunity to speak of it to Mr. Christie without finding any plausible 
explanation. I now regret that I did not carefully examine the 
places of contact, and observe, whether the surfaces brought to- 
gether and united at first by magnetic force, might not afterwards re- 
main so in the same way as the Magdeburg hemispheres. 
Magnetical observations were recommended to be made, during 
the appearance of the aurora borealis, and it was also requested that 
they should be made, as far as practicable, during all meteorological 
observations. Without denying the great advantages to be deri 
from observations taken with this view, I think much more might 
be gained from observations on the nature and intensity of atmos- 
pheric electricity, which I regard as one of the most important sub- 
jects of examination; this was also the opinion of Mr. Herschel. 
I have since seen at Paris the apparatus designed by M. Arago for 
this purpose, and with which he has made observations with an ac- 
curacy which will no doubt effect new discoveries for science. 
* Mr. Brunel, in a special communication, gave the details of the 
observations made by himself and Mr. Faraday, on the employment 
of the expansive force of liquid carbonic acid; observations which 
are still but too little known by those wbo endeavor to employ this 
substance in machinery instead of steam. These experiments, which 
were made with great care, prove that the carbonic acid gradually 
loses its elastic foree. Mr. Brunel was so good as to show me, at 
London, the designs of the apparatus of which he has availed 
himself. : 2 , 
Tides.—It had been recommended, last year, that attention should 
be devoted to the subject of tides. Mr. Whewell, who has just pub- 
lished, in the Philosophical Transactions of London, a very interest- 
ing memoir on this subject, and which has also received much atten- 
tion from Mr. Lubbock, read an interesting report, in which he re- 
capitulated all that has been achieved by science up to the present 
time. 
