Page:Popular Science Monthly Volume 14.djvu/629

Rh  we have been watching with our spectroscopes for the last ten years can not be explained on the existing-hypothesis, and that they are simply and sufficiently accounted for by supposing that primordial atoms are associated in the corona and dissociated in the reversing layer.

In this way the vertical currents in the solar atmosphere, both ascending and descending, the intense absorption in sun-spots, their association with the faculæ, and the apparently continuous spectrum of the corona, and its structure, find an easy solution.

We are yet as far as ever from a demonstration of the cause of the variation in the temperature of the sun; but the excess of so-called calcium with minimum sun-spots, and excess of so-called hydrogen with maximum sun-spots, follow naturally from the hypothesis, and afford indications that the temperature of the hottest region in the sun closely approximates to that of the reversing layer in stars of the type of Sirius and a Lyræ.



R. JOHN STUART MILL, in the preface to his work on "Logic and the Principles of Evidence," observes that while in the search for truth we may be able, in some cases, to avoid errors instinctively and successfully, although unable to formulate the method by which we do so, yet it is an advantage not to be dispensed with to have a rational understanding of the philosophy of reasoning, so that we shall not be forced to depend alone on blind and irregular instinct.

In experimenting with living human beings there are six sources of errors which instinctively physiologists and physicians sometimes guard against and allow for, but which ought to be and can be, as I contend, and shall here aim to prove, reduced to a positive science. As these elements of error come in the main from the nervous system, their study belongs preeminently to neurology, or the study of the nervous system in health and disease; and it is because of the backwardness of this specialty that the subject has been thus far passed by.

The deficiencies of our knowledge of this subject were forced on