SURVEY OF THE BRITISH ISLES B’OR THE EPOCH JANUARY 1, 1891. 17 
Our results are, however, entirely confirmed by those of Dr. Van Rijckevorsel, 
who has proved that the differences between tlie standards of several of the principal 
European Magnetic Observatories, are of the same order of magnitude as those shown 
above. 
Comparison at Kew of Horizontal Force Observations made with the Survey and 
Kevj Instruments. 
The calculations, by which the observations made with the Survey Instruments in 
1887 were compared with the Kew Standards, were repeated with the modifications 
above described, with tlie result that the difference between the Kew and Survey 
Instruments was practically unaltered, being reduced only from 0‘0029 to 0‘0023 
metric unit. 
When a comparison was being made, the defiection experiment was performed 
on each day with the Survey Instrument. The moment of the magnet was determined 
from this and from a vibration experiment made immediately before or after it. 
The vibration experiment was then repeated at intervals, the moment already 
determined being used in the calculations based on these additional observations. 
MDCCCXCVI.—A. 
d 
