88 AXNUAL OF SCIENTIFIC DISCOVERY. 



mediately commence to rotate, and move about with remarkable 

 energy ; varying sometimes in rapidity, but usually conducting their 

 gyrations in a strange and erratic manner. In order to obtain the best 

 effects, some precautions are necessary : thus, the camphor should be 

 tolerably pure, the piece employed should be cut and separated from 

 the large lump with a perfectly clean instrument, and contact with the 

 fingers should be scrupulously avoided. Moreover, the glass should be 

 quite clean and the water pure. When these conditions are satisfied, 

 the phenomena are very striking. In the Annual of Sci. Dls. for 1863, 

 p. 131, the account of some operations by Mr. Tomlinson of Lon- 

 don on this subject was published. The following additional mem- 

 oranda of interest have recently been laid before the public by Mr. 

 Lightfoot, another experimentalist. This latter gentleman states, 

 that if instead of using a torn or cut fragment from a lump of camphor, 

 one or two fine crystals are detached with a clean needle-point from the 

 cork of a phial in which camphor is kept, and these are let fall on 

 clean water, they at once begin to move about with wonderfully in- 

 creased rapidity, darting away in various directions, as if shot from 

 some miniature engine, or endowed with life and a will of their own ; 

 each crystal quivering and rocking on the water with an apparently 

 high degree of indignation at its ibrced contact with the humid sur- 

 face. This fury gradually diminishes, and a regular dance begins ; the 

 various particles select partners to some of which they wilt seem to 

 cling with pertinacity ; whilst others will either remain indifferent, or, 

 if attracted, will only stay a very short time in embrace, and wander 

 again in search of more congenial floating associates. The explana- 

 tions which Mr. Lightfoot gives of these movements is the emanation 

 of a vapor from the volatile camphor, which has a very low tension ; 

 the water upon which it floats being capable of dissolving and diffus- 

 ing this vapor more readily in certain directions of the crystalline axes, 

 thereby removes sufficient vapor pressure at those points for the oppo- 

 site side to drive about (by recoil) the nicely-suspended particle. In 

 certain positions two crystals of camphor will attract each other, whilst 

 in other situations there is a mutual repulsion. It will sometimes hap- 

 pen that two crystals of camphor may be thrown on the water and not 

 have any tendency to locomotion. When this is the case, a continual 

 trembling or vibration will be noticed in the crystal. When two such 

 stationary vibrating crystals come in contact by attraction, immediate- 

 ly an eccentric, irregular change of place occurs, as if the force agitat- 

 ing each previous to the grouping, produced a new resultant force, in 

 obedience to which the combined crystals move. 



As- above stated, it is of essential importance that in separating and 

 placing the camphor in water everything should be quite clean, and 

 that the fingers should not touch the camphor in any stage. The 

 reason of this is found in the circumstance that if camphor is actively 

 moving on water, and the most minute particle of certain greasy sub- 

 stances touch the water, instantaneously, as if by some magic, the cam- 

 phor is deprived of all motion. The scene of previous activity is changed 

 into immobility. This curious property has been made use of by Mr. 

 Lightfoot to detect grease in quantities so extremely minute as would 

 appear almost fabulous, for camphor cannot be made to rotate on water 

 containing the most infinitesimal portion of grease. Mr. Lightfoot has 



