on the Surface of Water. 41 9 



was shown in my original essay that essential oils did not per- 

 manently arrest the motions of camphor, but only so long as they 

 remained in the form of films on its surface. When these had 

 evaporated without leaving any residue or oxidized deposit, the 

 motions set in as before. But I now found that if the oils were 

 freed from oxidized products by being distilled in contact with a 

 bit of sodium or caustic potash, they did not arrest the motions 

 of the camphor at all. The fragments skated through them and 

 cut them up in all directions. The oils had so far improved in 

 cohesive force that they no longer formed films, but lenticular 

 masses with rounded edges. From ten to twenty drops of an 

 oil might thus be deposited on the water without interfering in 

 any way with the gyrations. Fragments of benzoic acid, ob- 

 tained by exposing oil of bitter almonds, or of Laurus cerasi, to 

 the air for some time, were singularly active below, in, and 

 among the oil. This showed that there was little or no adhe- 

 sion of the oils to the surface of the water ; so that the frag- 

 ments were as free to move as if the oil were not present. 



29. It was not until after reading Professor Van der Mens- 

 brugghe's memoir (note l ) that I attempted to repeat the expe- 

 riment of camphor on a raft on the surface of water (10) . It 

 was evident to me that if this were a true result, it would be 

 fatal to the reaction theory — although Prevost (14) and Biot (15) 

 insist on the force of the experiment, and explain it on the prin- 

 ciple of reaction on the air, while Carradori (13) is equally 

 energetic in denying the possibility of the experiment unless 

 there is reaction on the surface of the water. I placed camphor 

 on a tinfoil raft and also on cork, and never obtained any motion 

 unless the water wetted the camphor, or had some direct com- 

 munication with it. Professor Mensbrugghe suggests that my 

 rafts and their cargo of camphor were too heavy. I now see 

 that this was the case, and that the cork, from being too thick, 

 was too high out of the water. I formed a raft of a small square 

 of mica, placed on it a bit of camphor about the size of a small pea, 

 took up the raft on the point of a penknife, and so launched it 

 upon the surface of 6 ounces of water contained in a very clean 

 cohesion-figure glass 3 \ inches in diameter. Before the raft had 

 touched the water, a visible shudder passed over its surface, 

 showing the action of camphor at a distance, as in Biotas expe- 

 riment (15). No sooner was the raft fairly launched than it 

 began to sail about, and continued to do so with gradually 

 slackening effort during a whole week. The advantage of using 

 mica is that its surface is almost a fleur oVeau, and it sails about 

 without allowing the camphor to be disturbed or to become 

 wet. 



30. The principle upon which the new theory is based is that 



