44 
electric currents flowing on a spherical surface closely 
surrounding the earth and producing such magnetic effects 
as we observe in the diurnal variations. This part of my 
work has, like the rest, failed to secure Mr. Chambers’ 
approval. I do not doubt that Mr. Chambers did not intend 
to offer any but fair criticisms, and that nothing but radical 
misunderstanding can have induced him to make the remark 
which I shall presently quote. 
Supposing, to make my meaning clear by an example, Mr. 
Chambers had stated that the gravitational attraction of the 
earth on a point outside was nearly the same as that due 
to a particle placed at its centre, having a mass equal 
to the mass of the earth. Would Mr. Chambers have con- 
sidered it fair criticism on my part, if I had objected by 
saying: No reason is given why the different parts of 
the earth should be regarded as placed in the earth’s centre, 
and, until that is done, we can have no assurance that the 
character of the earth’s material is not such as to place it 
outside the class to which alone the formulae used apply ? 
It is criticism of exactly the same nature which Mr. 
Chambers uses when he objects to my representation of the 
diurnal period by means of imaginary surface currents, 
because: '“No reason is given why the stream-lines of the 
aerial currents should be regarded as dividing the earth’s 
surface into annuli, and until that is done, we have no 
assurance that their character is not such as to place them 
outside the class to which alone the formulae used can apply.” 
Any argument against such criticism is, of course, im- 
possible. 
In spite of considerable efforts, I have failed to discover 
any intelligible meaning to Mr. Chambers’ remarks on this 
part of my paper. 
There is one sentence, however, in my paper which I 
should like to qualify. I had explained why the currents 
