410 FIRST REPORT UPON MAGNETIC WORK

to Gilbert's dictum would be that the earth acts like a great magnet,
if it is not in itself a magnet. We do not as yet know definitely
whether the earth is a magnet or an electro-magnet, i. e., whether the
earth acts upon a freely suspended magnetic needle as a permanently
magnetized body, with definite magnetic poles or centers of attraction,
or whether it acts like a soft piece of iron rendered temporarily mag-
netic by a current of electricity circulating around it. To put the
matter tersely, no satisfactory answer has as yet been given to the
question: "Is the earth's magnetism permanent or induced?" We
know that the earth possesses magnetism in some form, but the how
and the whence, in spite of innumerable attempts of some of the most
brilliant minds to solve the riddles, are still mysteries.

Helmholtz characterized the earth's magnetism as one of the most
puzzling of natural forces.

Since it can be mathematically demonstrated that it is always pos-
sible to distribute electric currents within the earth's crust in such a
way that the external magnetic effect of these currents will be precisely
the same as that due to a system of permanent magnets embedded in
the earth, it follows that we can equally as well satisfy the magnetic
phenomena observed on the earth's surface, on either hypothesis.

The electric current theory has many points in its favor, but thus
far no adequate cause has been found, that is, one that would explain
not only qualitatively but also quantitatively the currents and the
direction in which they would have to proceed, i. e., roughly from east
to west around the earth. And Professor Schuster's question as to
whether every large rotating mass is a magnet has not yet been ex-
perimentally attacked. There is a strong suspicion that the earth's
rotatory motion has an important share in the production of the earth's
magnetism.

Furthermore, we as yet have no knowledge whatever with regard to
the actual distribution of magnetism within the earth's crust; nor
shall we ever have so long as we confine our observations entirely to
the surface of the earth. For an infinite number of distributions of
magnetism can be found which will satisfy surface phenomena.
What is needed is observations in the region above us—in balloons—