112 Proceedings of the Royal Society 
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 Umhilicalis 
and Placeuta. By Professor Simpson. 
3. On Earth-Currents during Magnetic Calms, and their 
Connection with Magnetic Changes. By Balfour Stewart, 
Esq., M.A., F.B.S. Communicated by Professor Tait. 
In two previous communications made by the author to the 
Koyal Society of London, it had been endeavoured to show that 
earth- currents and aurorae, 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. Y. 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, — 
Is^ class. Observations during moments of magnetic calm. 
2d „ Observations during minor magnetic disturbances. 
3d „ Observations during greater magnetic disturbances. 
