158 Proceedings of Societies. 
in direct metallic connection at the instant with the long open-air 
wire; and the magnets that were altered were in indirect connec- 
tion, or rather, in inductive position, for they were surrounded at 
the time by the wire coil of the pendulum-bob, whose composing 
wire is a connected continuation of the long open-air wire. 
To this it only remains to add, that these lightning-made mag- 
nets at the Castle clock, when duly replaced in the bundle suitably 
with their new poles, have given the most steady and satisfactory 
results in working the control of the clock ever since. 
2. Note on the Anatomical Type in the Funis Umbilicalis 
and Placenta. By Professor Simpson. 
3. On Earth-Currents during Magnetic Calms, and their 
Connection with Magnetic Changes. By Balfour Stewart, 
Esq., M.A., F.R.S. Communicated by Professor Tait. 
In two previous communications made by the author to the 
Royal Society of London, it had been endeavoured to show that 
earth-currents and auroree, which occur simultaneously with mag- 
netic storms, are secondary currents due to the small but abrupt 
changes in the magnetism of the earth which such storms denote. 
Earth-currents also occur during periods of magnetic calm, but they 
can then be rendered visible only by means of a delicate gal- 
vanometer. 
Such has been constructed by Mr C. V. Walker, who has by its 
means registered those earth-currents which occurred during the 
three last months of 1851, a period of magnetic calm. 
The object of the present communication is to discuss those 
observations of Mr Walker in connection with the simultaneous 
changes which took place in the values of the declination and 
the horizontal force component of the earth’s magnetism, these 
changes being furnished by means of continuously acting magneto- 
graphs at Kew Observatory. By this method Mr Walker’s obser- 
vations were divided into three classes,— 
Ist class, Observations during momeuts of magnetic calm. 
2d  ,, Observations during minor magnetic disturbances. 
3d  ,, Observations during greater magnetic disturbances. 
In the first of these classes a law of hours was manifestly ob- 
served, the values of the earth-currents for the hours of the night 
being extremely small. But in the second, and especially in the 
third class, the law of hours was observed to fail; and in the latter 
of these classes the peculiar action of disturbances was very mani- 
fest, the tendency of such disturbances being to create very strong 
earth-currents at the moment of their occurrence; and it is notice- 
able that these earth-currents were as often positive as negative. 
It was remarked by the author, that the very great strength of 
those earth-currents, which take place at the moments of disturb- 
ance, is in favour of the theory of induction, since the peculiarity 
