TORBENTS, ETC, BY qOSTA t»B BASTKUCA, 115 



part of the stream. The lumbermen affirm that, while rivers are rising, 

 the water is highest in the middle of the channel, and tends to throw float- 

 ing objects shorewards ; while they are falling, it is lowest in the middle, 

 and floating objects incUne towards the centre. Logs, they say, rolled into 

 the water during the rise, are very apt to lodge on the banks, while those 

 set afloat during the falling of the waters keep in the current, and are car- 

 ried without hindrance to their destination; and this law, which has been a 

 matter of familiar observation among woodmen for generations, is now 

 admitted as a scientific truth." 



A phenomenon similar to that reported by the lumbermen of America 

 may be observed in the rising and falling of mercury in a barometer tube. 

 When rising, the surface of the mercury is convex ; when falling, it is con- 

 cave ; and so constantly is this the case, that directions have been given 

 to observe whether the surface be convex or concave, to determine, irres- 

 pective of the pointer, whether the mercury be rising or falling. The 

 explanation is to be sought for in the relative strength of the attraction of 

 cohesion keeping the particles of the fluid mass together, and the attraction 

 of adhesion attaching them to the surface of the confining body, together 

 with a third element, that of velocity of movement, which may be relatively 

 difl^erent in its effect upon the two attractions named. 



This explanation of how the phenomena reported are brought about, 

 taken in connection with phenomena which are cited by M. Costa, enables 

 us to see how it may come to pass that destructive effects on the banks of 

 rivers are frequently produced by the floatage of timber. In many cases 

 the injurious effects produced upon lands by the clearing away of forests 

 are increased by measures adopted in bringing the felled trees out of the 

 forest, and in sending the timber to its first destination. By Marsh, in 

 speaking of a common practice followed in America and elsewhere, it is said, 

 — " The lumbermen usually haul the timber to the banks of the river in the 

 winter, and when the spring floods swell the streams and break up the ice, 

 they roll the logs into the water, leaving them to float down to their desti- 

 nation. If the transporting stream is too small to furnish a sufficient 

 channel for this rude navigation, it is sometimes dammed up, and the timber 

 is collected in the pond thus formed above the dam. When the pond is full a 

 sluice is opened, or the dam is blown up or otherwise suddenly broken, and 

 the whole mass of timber above it is hurried down with the rolling flood. 

 Both of these ways of proceeding expose the banks of the rivers employed 

 as channels of floatation to abrasion ; and in some of the American States 

 it has been found necessary to protect, by special legislation, the lands 

 through which they flow from the serious injury sometimes received through 

 the practice described." 



And in reference to the bringing of felled trees out of the forest, he says, 

 in an appendix, — "The methods of transporting timber employed by the 

 lumbermen in the Alps are often more destructive than the baring of the 

 soil. Forests frequently grow in Alpine glens, or other mountain localities, 

 inaccessible to wheeled vehicles or even to sleighs. In such cases the 

 timber is sent down by slides, which, if long used, become the beds of new 

 torrents or it is conveyed to larger streams by the method of floatation 

 described. 



" The Rapport au Conseil Fdderal sur les Torrents, des Alpes Smsses inspectes 

 en 1858-63, published at Lausanne in 1865 [that commented on by M. 

 Cezanne] gives a great amount of information respecting this scourge and 



