45 
whicli I desired to investigate were nearly at right angles 
to the magnetic force at the point, and how to obtain 
approximate expressions for their intensity. But in the ex- 
planation of the numbers which I give in a table, I make 
the following remark: “The direction of the current is as 
accurate as the observations will permit; the intensity is 
calculated, as explained above, by multiplying the magnetic 
force by 5/12 tt, and is, therefore, approximate only as far as 
its absolute value is concerned, but the relative value of the 
numbers ought to be correct.” The first part of the sentence 
is true only on the supposition that the magnetic force is 
strictly normal to the current, which it is not. The second 
part is not quite correct, the relative values of the numbers 
will also be approximate only. 
The approximation is, however, quite near enough for the 
purpose for which the table was calculated. 
I need not enter into what may be called the ornamental 
part of Mr. Chambers’ paper, except to express my regret 
that he should have felt hurt by a remark of mine about the 
times for which he reduces his mesurements. 
I was aware that he was following the recommendations 
which a committee of the Koyal Society framed about the 
year 1840 ; T was also aware that in the opinion of the 
committee” . , . “ it was at that time so important that each 
instrument of the same name, should read simultaneously at 
the different observatories, that they embodied in their 
instructions to observers specific directions that the hours of 
observation were to be read in a particular order, and at 
equal intervals,” 
But I knew, in addition, that since that time it was found 
that the diurnal variations depended chiefly on the local 
time of the place, and not on Gottingen time, so that in con- 
sequence, every observatory of note took the first opportunity 
of departing from the original recommendations. 
