356 On the Windings of Rivers in Alluvial Plains. [June 21 , 



physical science an experiment more conclusive nor an inference more 

 certain than this one. Now, supposing the powder to be light enough to 

 float in the air, and that we are enabled to see it there as plainly as the 

 heavier powder in the palm of the hand. If, like the powder, such 

 floating dust, sown in an appropriate soil, produce a definite living crop, 

 with the same logical rigour as before we should conclude that the germs 

 of this crop must have formed a portion of the dust." This reasoning 

 applies, word for word, to the development of Bacteria from those 

 suspended particles which the luminous beam reveals in the air, and in 

 the absence of which life is never generated in previously sterilized 

 infusions. 



I respectfully submit this reasoning to Dr. Sanderson's friendly con- 

 sideration. 



VI. ce Experimental Demonstration in respect to the Origin of 

 Windings of Rivers in Alluvial Plains_, and to the Mode of 

 Flow of Water round Bends of Pipes." By Professor 

 James Thomson, LL.D._, D.Sc, F.R.S. Received June 21, 

 1877. 



In a paper which I had the honour of submitting to the Royal Society 

 rather more than a year ago, and which is printed in the ' Proceedings ' 

 for May 4, 1876, I proposed, on hydrokinetic principles, a theoretical 

 view of the mode of flow of water round bends of rivers and of pipes, 

 and offered under that view explanations of the origin of the windings 

 of rivers flowing through alluvial plains. Wishing to bring under the 

 test of experiment the views then put forward, and to render very clearly 

 perceptible the phenomena anticipated, I constructed, in the summer of 

 1876, a small artificial river, about eight inches wide and an inch or two 

 deep, having a bend turning about a half-round, or 180°, so that the 

 course of the river might be likened to the capital letter \J. The water 

 flowing in this river showed very completely, and very remarkably, the 

 phenomena which had been anticipated, and which are to be found 

 described in the paper referred to. The courses of the water's flow at 

 the various parts of the river, along the bed, and at the upper surface, 

 and at places anywhere within the body of the current, were made to 

 show themselves in several ways. One way was by means of threads of 

 suitable length (about an inch or two long), some of which were anchored 

 at bottom, while others were attached at various depths in the river to 

 pins or slender wires standing upright like thin posts in the river. These 

 threads, by the lines of direction which they assumed, showed very well 

 the directions of the flow at bottom and at various depths. Another 

 way, and one which proved very satisfactory for showing the bottom cur- 

 rents, was by dropping into the river granules of various kinds, such as 



