PHYSICAL EXPERIMENTS. 49 



A drop of a solution of camphor in sulphuric acid, 

 gently delivered to the surface of the water, will take a 

 double-convex lens shape, and will move about the 

 water in an eccentric manner for a long time. Several 

 drops may be placed upon the water at a time, but they 

 will avoid each other in their movements. Make a 

 small boat of tin-foil, and into it put a fragment of cam- 

 phor about the size of a pea, and place it on the tank 3 

 it may move round slowly, but put a piece of camphor, 

 about the size of a canary-seed, upon the water, and it 

 will spin round, dart up to the boat, and drag it about 

 in a lively manner, just as an insect might do. 



To show the existence of the camphor-film, that forms 

 upon the surface as soon as it touches it, dust the sur- 

 face of the water with lycopodium, then gently lower a 

 fragment of camphor upon the middle of the tank. 

 The instant the camphor touches the water the dust 

 will be seen to open out into a circle of large di- 

 ameter ; then, after a moment's pause, the lycopodium 

 is formed into a number of wheels, arranged in pairs, 

 revolving in opposite directions. 



A large drop of camphor dissolved in benzole, 

 dropped upon water, has the appearance of a double 

 convex lens ; it sails slowly about for a while, becoming 

 flatter and thinner, till at last it has sudden contrac- 

 tions, assuming different shapes. The contractions 

 multiply till at length they become so violent as to throw 

 off portions of the disk, or split up into smaller disks, 

 which, in their turn, twist and double up, and ultimately 

 throw out from each a tiny film of camphor, which lies 

 quiet upon the water. 



One who is interested to pursue this subject further 

 will find an abundance of material by Tomlinson, in 

 the Philosophical Magazine for 186 1. Also in " Experi- 

 mental Essays," Weale's Series, No. 143. 



