116 Mr. C. Tomlinson on the Action of 



ness, combine with it, and form a film which sometimes displays 

 colour. 



Taking solution as one of the keys, if not the master-key, to 

 these experiments, and defining it as you do in your ' Chemical 

 Physics ' as a case of adhesion of a liquid to a solid (often over- 

 coming cohesion), or of a liquid to a liquid, and moreover defi- 

 ning saturation as an equilibrium between the forces of adhesion 

 and cohesion, I began to see more clearly the rationale of my 

 numerous experiments. In order to test the adhesion view of 

 the case, I looked about me for some fluid of nearly the same 

 density as water, with but slight adhesion to it (that is, very 

 sparingly soluble in it), but one which would readily saturate a 

 moderate quantity of water (that is, a liquid whose cohesion 

 would soon balance the adhesion of the water), so that whatever 

 visible action might take place between the two would admit of 

 being renewed from time to time by increasing the quantity of 

 the water. After many trials I found exactly what was required 

 in creosote. Although this substance is slightly heavier than 

 water (spec. grav. 1*059), yet by carefully delivering a drop to 

 the surface of water from the end of a glass rod it will not sink; 

 the under surface of the drop will, however, present a convex 

 bulge below the general surface of the water. 



I wonder whether it ever occurred to a chemist to place a drop 

 of creosote on the surface of water. It presents a most singular 

 appearance : it flattens out into a disc with a silvery reflexion of 

 the light, and sails about on the water with some speed, while it 

 is all the time rapidly agitated with a motion that gives it the 

 appearance, of a living creature. Its edge vibrates with rapid 

 crispations; it darts out small globules, which immediately 

 begin a series of motions of rotation and translation on their 

 own account. In the mean time a silvery film of creosote spreads 

 over the surface of the water: the parent globule and the smaller 

 globules become less energetic; they perform a number of mo- 

 tions among themselves, moving about in circular or curved paths, 

 carefully avoiding each other, and reminding one of the water 

 insects which may be seen sporting on the surface of a pond 

 in summer. Sometimes the larger globules will remain still, 

 and the smaller ones will rotate in little lakes, which they 

 seem to clear out for themselves in the film to disport in. 

 After some time they all come to rest ; but again begin to move 

 for a time, once more to come to rest, and, it may be, again to 

 rotate. 



Now there is evidently a struggle going on between the cohe- 

 sion of the drop and the adhesion of the water. These two 

 forces are so nicely balanced that it seems doubtful for a time 

 which will prevail. The water tends to adhere to and diffuse the 



