374 SCIENCE IN SHORT CHAPTERS. 



edge of the precipice as a great overhanging sheet or cor- 

 nice, which bent down as it was pushed forward, and pre- 

 sented on the convex side of the sheet some fine blue 

 cracks, or "crevasses" as they are called. These gradually 

 widened and deepened, until the overhanging mass broke 

 off and fell into the lake, on the surface of which I saw the 

 result, in the form of several floating icebergs that had pre- 

 viously fallen. 



Something like this, on a small scale, may be seen at 

 home on the edge of a house roof, on which there has been 

 an accumulation of snow; but, in this case, it is rather 

 sliding than flowing that has made the cornice; but its 

 down-bending is a result of viscosity. 



These and a multitude of other facts that might be 

 stated, many of which will occur to the reader, prove 

 clearly enough that the solid and liquid states of matter 

 are not distinctly and broadly separable, but are connected 

 by an intermediate condition of viscosity. 



We now come to the question whether there is any simi- 

 lar continuity between liquids and gases. Ordinary expe- 

 rience decidedly suggests a negative answer. We can point 

 to nothing within easy reach that has the properties of a 

 liquid and gaseous half-and-half; that stands between gases 

 and liquids as pitch and treacle stand between solids and 

 liquids. 



Some, perhaps, may suggest that cloud-matterLondon 

 fog, for example is in such an intermediate state. This, 

 however, is not the case. White country fog, ordinary 

 clouds, or the so-called "steam" that is seen assuming cloud 

 forms as it issues from the spout of a tea-kettle or funnel 

 of a locomotive, consists of minute particles of water sus- 

 pended in air, as solid particles of dust are also suspended. 

 It has been called "vesicular vapor," on the supposition 

 that it has the form of minute vesicles, like soap-bubbles 

 on a very small scale, but this hypothesis remains unproven. 

 London fog consists of similar particles, varnished with a 

 delicate film of coal-tar, and intersprinkled with particles 

 of soot. 



In order to clearly comprehend the above-stated question, 

 we must define the difference between liquids and 



