84 



THE FORMS OF WATER 



and life. 



Wishing, moreover, to render them of per- 

 manent value, I wrote out copious Notes ol 

 the course, and had them distributed among 

 the boys and girls. In preparing these Notes 

 I aimed at nothing less than presenting to my 

 youthful audience, in a. concentrated but 

 perfectly digestible form, every essential 

 point embraced in the literature of the gia- 

 ciers, and some things in addition, which, 

 derived as they were from my own recent 

 researches, no book previously published on 

 the subject contained. 



E'.H my theory of education agrees with 

 th*5 v>f JSmeraoii. according to which instruc- 

 tion is only half the battle, what he calls 

 provocation being the other half. By Ihis he 

 means that power of the teacher, through 

 the force of his character and the vitality of 

 his thought, to bring out all the latent 

 strength of his pupil, and to invest with in- 

 terest even the driest matters of detail. In 

 the present instance I was determined to 

 shirk nothing essential, however dry ; and, 

 to keep my mind alive to the requirements 

 of my pupil, I proposed a series of ideal 

 rambles, in which he should be always at my 

 side. Oddly enough, though 1 was here 

 dealing with what might be called the ab- 

 stract idea of a boy, I realized his presence 

 so fully as to entertain for him, before our 

 excursions ended, an affection consciously 

 warm and real. 



The Notes here referred to were at first 

 intended for the use of my audience alone. 

 At the urgent request of a friend I slightly 

 expanded them, and converted them into the 

 little book here presented to the reader. 



The amount of attention bestowed upon 

 the volume induces me to give this brief 

 history of Us origin. 



A German critic, whom I have no reason 

 to regard as specially favorable to me or it, 

 makes the following remark on the style of 

 the book : " This passion [for the mountains] 

 tempts him to reveal more of his Alpine 

 wanderings than is necessary for his demon- 

 strations. Thu reader, however, will not 

 find this a disagreeable interruption of the 

 couise of thought; for the book thereby 

 gains wonderfully in vividness." This, I 

 would say, was the express aim of the breaks 

 referred to. I desired to keep my companion 

 fresh, as well as instructed, and these inter- 

 ruptions were so many breathing-places 

 where the intellectual tension was purposely 

 relaxed and the mind of tlie pupil braced to 

 fresh action. 



Of other criticisms, flattering and other- 

 wise, I forbear to speak. A>5 regards some 

 ftf them, indeed, it would be a reproach to 

 that manliness which I have sought to en- 

 courage in my pupil to return blow for blow. 

 If the reader be acquainted with them, this 

 will let him know how I regard them ; and 

 if he be not acquainted with them, I wouM 

 recommend him to ignore them, and to form 

 his own judgment of this book. No fair- 

 minded person who reads it will dream that 

 I, in writing it, had thought of acting other- 



wise than justly and generously toward K:? 

 predecessors, the last of whom, 1o the grief 

 of all who knew him, has recently passed 

 away. JOHN TYNDALL. 



APBIL, 1874. 



1. CLOUDS, RAINS, AND RIVERS. 



1. EVERY occurrence in Nature is preceded 

 by otner occurrences which arc its causes, 

 and succeeded by others which arc its effects. 

 The human mind is not satisfied with observ- 

 ing and studying any natural occurrence, 

 alone, but takes pleasure in connecting every 

 natural fact with what has gone before if. 

 and with what is to come after it. 

 _ 2. Thus, when we enter upon the study of 

 rivers and glaciers, our interest will bo great- 

 ly augmented by taking into account not 

 only their actual appearances, but also their 

 causes and effects. 



o. Let us trace a river to its source. Be- 

 ginning where it empties itself into the sea, 

 and following it backward, we find it from 

 time to tinu joined by tributaries which 

 swell its waters. The river of course be- 

 comes smaller as these tributaries are passed. 

 It shrinks first to a brook, then to a stream ; 

 this again divides itself into a number of 

 smaller streamlets, ending in mere threads of 

 water. These constitute the source of tlu 

 river, and are usually found among hills. j 



4. Thus the Severn lias its source in th.>' 

 Welsh Mountains ; the Thames in the Cots- 

 wold Hills ; the Danube in tin? hills of tlie 

 Black Forest ; the Rhine and the Rhone in 

 the Alps ; the Ganges in the Himalaya 

 Mountains ; the Euphrates near Mount Ara 

 rat ; the Garonne in t.'ie Pyrenees ; the- Elbe 

 in the Giant Mountains of I5oheni.':i ; tho 

 Missouri in the Rocky Mountains, and the 

 Amazon in the Andes of Peru. 



5. But it is quite plain that we have not 

 yet reached the real beginning of the liters. 

 Whence do the earliest streams derive their 

 water? A brief residence among tlie moun- 

 tains would prove to you that they are fed 

 by rains. In dry weather you would find 

 the streams feeble, sometime? indeed quitu 

 dried up. In wet weather yc'i would see 

 them foaming torrents. la general these 

 streams lose themselves as littlo threads of 

 water upon the hill-sides ; but. srmcliuies you 

 may trace a river to a definite spring. Tho 

 river Albula in Switzerland, for instance, 

 rushes at its origin in considerable volumo 

 from a mountain-side. But you very soon 

 assure yourself that such springs are also fed 

 by rain, which has percolated through the 

 rocks or soil, and which, through some ori- 

 fice that it has found or formed, comes to the 

 light of day. 



0. But we cannot end here. Whence 

 comes the rain which forms the mountain 

 streams? Observation enables you to an- 

 swer the question. Rain does not'come from 

 a clear sky. It comes from clouds. But 

 w T hat are clouds ? Is there nothing you are 

 acquainted with which they resemble ? You 

 discover at once a likeness between them and 

 the condensed steam of a locomotive. 'At 



