Royal Society. 389 



water, with a fair amount of detritus aud a swift current, the results 

 of corrasion will be proportionately rapid, and gorges, such as those 

 of Colorado, the inevitable result. Then, again, the evenness of 

 the river-bed, even when cut through rocks of various degrees of 

 hardness, depends on the relation of corrasion to transportation. 

 There are no waterfalls in the great canons, though hard bands of 

 limestone as well as adjacent beds of soft sandstone are equally 

 cut through. Ordinarily this would result in the production of 

 ledges and waterfalls ; but there are none such in these river-beds. 

 The even volume of water from a distant source, the regular velo- 

 city of the current, the nature and amount of the debris, lead rather 

 to an equalization of the channel than to its abrupt change. " A 

 stream which has a supply of debris equal to its capacity, tends to 

 build up the gentler slopes and cut away the steeper." With less 

 material and an equally rapid current, the wear would be unequal ; 

 but evenness of corrasion is the natural outcome of a state of things 

 similar to that which characterizes the great rivers of Colorado. 



In fact it may be said that the cause of the gorge of the Colo- 

 rado region is due, first, to the general dryness of the plateau, and 

 consequent diminished weathering, while still into the area, and 

 through the probably original fissures, large volumes of water, pro- 

 cured from a distant source, roll down a steep declivity, laden with 

 hard " tools " of stone ; and the regularity of the current has tended 

 to the steady continuous wearing-down of the rocks, unaided by 

 much local weathering, which, had it been present, would have 

 sooner or later converted the precipitous sides of the great canons 

 into wide river-valleys. 



The pamphlet deals little with any general description of the 

 terrain. It is in its entirety an argument in favour of the view 

 that the great canons are the simple result of ceaseless even water- 

 action ; and, as such, it is not only most interesting and instructive, 

 but most readable. 



LIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 311.] 



June 15, 1876. — Dr. J. Dalton Hooker, C.B., President, in the Chair. 



rPHE following paper was read : — 



■*- " Experiments on Contact Electricity between Non-Conduc- 

 tors." By Joseph Thomson, Student at the Physical Laboratory of 

 Owens College. 



It was observed that when a plate of copper was lifted from a 

 plate of glass the copper was electrified, and also that when a plate 

 of glass was lifted from a plate of wax the glass was electrified, 

 care being taken to have as little friction as possible ; it was after- 

 wards found that the former experiment had already been made by 

 Fechner (see Wiedemann's ' Galvanismus,' page 21), who also tried 

 lifting copper from sulphur and got the same effect ; although the 



