35 
converse process of examining whether the calculated cur- 
rents conform to the required condition or not, it must he 
presumed that the necessity of their doing so was not 
recognised. 
In the course of his discussion of this matter, the writer 
makes a statement of fact, and adds an insinuation which it 
behoves me to notice. His words are, “ The Bombay obser- 
vations on magnetic declination refer, as regards time, to 
twelve minutes past each hour. The observations at the 
same place on horizontal force to fourteen minutes past each 
hour. This is only one of the many little devices by means 
of which the heads of magnetical observatories try to enliven 
the time of those who want to compare their results.” It is 
strange that he should seem to be unaware that the Bombay 
Observatory is one of the number of Colonial and Indian 
Observatories established under the auspices of the Koyal 
Society about the year 1840 ; and that in the opinion of the 
Committee of Physics of that Society — consisting of men of 
the calibre and repute of J ohn Herschel], Sabine, Lloyd, &c. 
■ — it was at that time so important that each instrument of 
the same name should be read simultaneously at the dif- 
ferent observatories, that they embodied in their instructions 
to observers specific directions that the hours of observation 
were to be hours of Gottingen mean time, and the instru- 
ments were to be read in a particular order and at equal 
intervals. I need only add that the longitude of Bombay 
east from Gottingen is 4h. lljm., and that the results 
which the writer has ma'de use of were derived from eye- 
observations taken hourly for over a quarter of a centuiy in 
pursuance of the Bojml Society’s instructions. 
And, now, briefiy to summarise my criticism of the paper 
as a whole : — 
(1) Whereas the principal feature of Gauss’s theory is to 
contemplate the magnetic forces through the potential 
