Part 1 (1/2)
The Glaciers of the Alps.
by John Tyndall.
PREFACE.
In the following work I have not attempted to mix Narrative and Science, believing that the mind once interested in the one, cannot with satisfaction pa.s.s abruptly to the other. The book is therefore divided into Two Parts: the first chiefly narrative, and the second chiefly scientific.
In Part I. I have sought to convey some notion of the life of an Alpine explorer, and of the means by which his knowledge is acquired. In Part II. an attempt is made to cla.s.sify such knowledge, and to refer the observed phenomena to their physical causes.
The Second Part of the work is written with a desire to interest intelligent persons who may not possess any special scientific culture.
For their sakes I have dwelt more fully on principles than I should have done in presence of a purely scientific audience. The brief sketch of the nature of Light and Heat, with which Part II. is commenced, will not, I trust, prove uninteresting to the reader for whom it is more especially designed.
Should any obscurity exist as to the meaning of the terms Structure, Dirt-bands, Regelation, Interference, and others, which occur in Part I., it will entirely disappear in the perusal of Part II.
Two ascents of Mont Blanc and two of Monte Rosa are recorded; but the aspects of nature, and other circ.u.mstances which attracted my attention, were so different in the respective cases, that repet.i.tion was scarcely possible.
The numerous interesting articles on glaciers which have been published during the last eighteen months, and the various lively discussions to which the subject has given birth, have induced me to make myself better acquainted than I had previously been with the historic aspect of the question. In some important cases I have stated, with the utmost possible brevity, the results of my reading, and thus, I trust, contributed to the formation of a just estimate of men whose labours in this field were long anterior to my own.
J. T.
_Royal Inst.i.tution, June, 1860._
PREFATORY NOTE.
”Glaciers of the Alps” was published nearly six and thirty years ago, and has been long out of print, its teaching in a condensed form having been embodied in the little book called ”Forms of Water.” The two books are, however, distinct in character; each appears to me to supplement the other; and as the older work is still frequently asked for, I have, at the suggestion of my husband's Publishers, consented to the present reprint, which may be followed later on by a reprint of ”Hours of Exercise.”
Before reproducing a book written so long ago, I sought to a.s.sure myself that it contained nothing touching the views of others which my husband might have wished at the present time to alter or omit. With this object I asked Lord Kelvin to be good enough to read over for me the pages which deal with the history of the subject and with discussions in which he himself took an active part. In kind response he writes:--”... After carefully going through all the pa.s.sages relating to those old differences I could not advise the omission of any of them from the reprint. There were, no doubt, some keen differences of opinion and judgement among us, and other friends now gone from us, but I think the statements on controversial points in this beautiful and interesting book of your husband's are all thoroughly courteous and considerate of feelings, and have been felt to be so by those whose views were contested or criticised in them.”
The current spelling of Swiss names has changed considerably since ”Glaciers of the Alps” was written, but, except in the very few cases where an obvious oversight called for correction, the text has been left unaltered. Only the Index has been made somewhat fuller than it was.
L. C. T.
_January, 1896._
INTRODUCTORY.
In the autumn of 1854 I attended the meeting of the British a.s.sociation at Liverpool; and, after it was over, availed myself of my position to make an excursion into North Wales. Guided by a friend who knew the country, I became acquainted with its chief beauties, and concluded the expedition by a visit to Bangor and the neighbouring slate quarries of Penrhyn.
From my boyhood I had been accustomed to handle slates; had seen them used as roofing materials, and had worked the usual amount of arithmetic upon them at school; but now, as I saw the rocks blasted, the broken ma.s.ses removed to the sheds surrounding the quarry, and there cloven into thin plates, a new interest was excited, and I could not help asking after the cause of this extraordinary property of cleavage. It sufficed to strike the point of an iron instrument into the edge of a plate of rock to cause the ma.s.s to yield and open, as wood opens in advance of a wedge driven into it. I walked round the quarry and observed that the planes of cleavage were everywhere parallel; the rock was capable of being split in one direction only, and this direction remained perfectly constant throughout the entire quarry.
[Sidenote: CLEAVAGE OF SLATE ROCKS.]
I was puzzled, and, on expressing my perplexity to my companion, he suggested that the cleavage was nothing more than the layers in which the rock had been originally deposited, and which, by some subsequent disturbance, had been set on end, like the strata of the sandstone rocks and chalk cliffs of Alum Bay. But though I was too ignorant to combat this notion successfully, it by no means satisfied me. I did not know that at the time of my visit this very question of slaty cleavage was exciting the greatest attention among English geologists, and I quitted the place with that feeling of intellectual discontent which, however unpleasant it may be for a time, is very useful as a stimulant, and perhaps as necessary to the true appreciation of knowledge as a healthy appet.i.te is to the enjoyment of food.
On inquiry I found that the subject had been treated by three English writers, Professor Sedgwick, Mr. Daniel Sharpe, and Mr. Sorby. From Professor Sedgwick I learned that cleavage and stratification were things totally distinct from each other; that in many cases the strata could be observed with the cleavage pa.s.sing through them at a high angle; and that this was the case throughout vast areas in North Wales and c.u.mberland. I read the lucid and important memoir of this eminent geologist with great interest: it placed the data of the problem before me, as far as they were then known, and I found myself, to some extent at least, in a condition to appreciate the value of a theoretic explanation.