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THE POPULAR SCIENCE MONTHLY. 



tain a layer more soluble than the rest, along 

 which the rock splits and peels. Compact 

 rocks like granite are traversed by parallel 

 joints on which the weather acts destruc- 

 tively ; and the less compact clays, dried to 

 powder, are blown by the wind and swept 

 more rapidly into rivers, lakes, and the sea. 

 Tbe rain-streams, always running over the 

 same channels, furrow the hill-side and wear 

 it away still more rapidly ; and a sheep-walk 

 in a few years may become a deep ravine. 

 The material carried down, when spread at 

 lower levels, helps to form plains like mead- 

 ows, and these in time may be cut through and 

 partially carried away. Streams descending 

 from peaty regions are charged with car- 

 bonic acid, and destructive to limestone. In 

 all mountain regions the rivers are liable to 

 enormous increase in volume from heavy 

 rainfalls, when they carry off proportion- 

 ately larger quantities of earth. The work 

 of springs is like that of rain and rivers. 

 The sink-holes in limestone regions carry 

 the water down underground to do a similar 

 work there ; and this underground flow of 

 water often helps in the production of land- 

 slips, especially when the ground is covered 

 with bowlder-clay. 



Teaching the "New Botany."— In the 



" New Botany," as described by Prof. W. J. 

 Beal, in Garden and Forest, pupils are set to 

 studying plants before books. Previous to 

 the first lesson, "each pupil is furnished 

 or told where to procure some specimen 

 for study. If it is winter, and flowers or 

 growing plants can not be had, give each a 

 branch of a tree or shrub, which may be 

 two feet long. The examination of these is 

 made during the usual time for preparing 

 lessons, and not while the class is before 

 the teacher. For the first recitation each is 

 to tell what he has discovered. The speci- 

 mens are not in sight during the recitation. 

 In learning the lesson, books are not used ; 

 for, if they are used, no books will contain a 

 quarter of what the pupil can see for him- 

 self. If there is time, each member of the 

 class is allowed a chance to mention any- 

 thing not named by any of the rest. The 

 pupils are not told what they can see for 

 themselves. An effort is made to keep 

 them working after something which they 

 have not yet discovered. If two members 



disagree on any point, on the next day, 

 after further study, they are requested to 

 bring in all the proofs they can, to sustain 

 their different conclusions. Give other 

 specimens for the next lesson, keep review- 

 ing, and generalize as details and facts ac- 

 cumulate. I like to give two species for 

 careful comparison. . . . After a few weeks, 

 reviews may be made in connection with 

 chapters in some book. I make it a rule to 

 give pupils specimens for study and com- 

 parison regarding every chapter in Gray's 

 Structural Botany before the book-lesson is 

 studied. I place no stress on making these 

 investigations in the order in which the 

 chapters of a text-book are arranged. Free 

 use is made of our botanic garden, the crops 

 in the vegetable-garden, fields, and experi- 

 ment station, and the thickets along the 

 river. Special topics are often assigned, in 

 which each student has to go many times 

 to observe and record observations on his 

 growing plant." Illustrations by drawing 

 are a prominent feature of the whole course. 



Leaning Towers.— The leaning tower of 

 Pisa is not the only building of its kind. 

 There are many towers in northern Italy that 

 deviate from the perpendicular, so that a 

 writer has spoken of the country as " a land 

 of towers staggering in all directions like 

 tipsy men " ; and there are in England few 

 spires of any great altitude that are quite 

 upright. The inclination of the Italian towers 

 is a result of the character of the foundation 

 soil, and of mistakes in building. The soil 

 and subsoil of northern Italy down to the 

 water-level are composed of rounded stones 

 brought down by torrents and rivers from 

 the Alps. A broad foundation is a primary 

 condition of the stability of buildings erected 

 upon it. The builders of the towers had 

 classic models in their eyes, and did not con- 

 template the broadening of bases or the add- 

 ing of buttresses to insure stability. Con- 

 sulting appearances, and not venturing to 

 depart from the conventional, they built 

 straight up. The pressure concentrated on 

 the narrow base was too much for the shift- 

 ing stones beneath. They yielded at the 

 weaker points, and the towers bent over. 

 If the builders had minded the example of 

 their Gothic neighbors and widened their 

 bases, the load would have been more evenly 



