On Camphor Pulsations. 19 



of pulsations or waves, which rise up so that their crest may be 

 one, two, or three-tenths of an inch above the general surface 

 of the water. These variations in height are marked by a series 

 of curved grooves or ripple lines on the sides of the camphor, 

 which gradually changes its dull translucent appearance for a 

 bright transparent one, showing that the water has penetrated 

 it. In the meantime an incision is made in the camphor, which 

 goes on increasing as successive films are detached, until at 

 last the stick is cut through, and the submerged piece com- 

 mences a series of gyrations on its own account. 



If lycopodium powder be faintly dusted over the surface, 

 the camphor currents and pulsations may on a fine day be seen 

 together. If two sticks of camphor be lowered into the same 

 surface of water, the interference of the currents will be shown 

 by the motions of the powder. 



As in the case of small fragments of camphor rotating 

 rapidly on the surface of water, the rotations are stopped if 

 the water be touched with a fatty oil, so these pulsations are 

 immediately arrested if the water be touched with a drop of 

 any substance which spreads into a film, and arrests evapora- 

 tion. The point of a pin dipped into olive oil and brought 

 into contact with the water, at once arrested the lycopodium 

 currents, a second contact stopped the pulsations. So also, 

 if a body be added to the water that satisfies its adhesion, 

 or, in other words, stops the solution, the pulsations are 

 arrested. Thus a drop of oil of camphor will stop the pulsa- 

 tion by depriving the water of the power of dissolving cam- 

 phor; a drop of olive oil will stop the pulsations by preventing 

 the water from evaporating ; but a drop of oil of bitter almonds, 

 which speedily evaporates, will allow the pulsations to go on 

 again very soon after it has been added. Turpentine, oil of 

 cajeput, kreosote, etc., stop the pulsations ; but ether, alcohol, 

 benzole, naphtha, bisulphide of carbon, caustic potash, and 

 sal-ammoniac, allow them to go on freely. A bit of sponge tied 

 to the end of a glass rod, if dipped in ether and held near the 

 camphor, will hold up the wave of water against the camphor 

 for some time. A drop of benzole does not stop the pulsations, 

 but it makes them less rapid. The pulsations will go on in a 

 solution of caustic potash and in one of sal-ammoniac, and I 

 have no doubt that the action of acids, etc., on rotating cam- 

 phor as described in my first " Experimental Essay," will have 

 a similar action on the camphor pulsations. 



In your notice of my book you say that I do " not seem by 

 any means to have exhausted the curious subject of the Storm 

 Glass." I had reserved this subject for a separate essay, a copy 

 of which I hope to have the pleasure of sending you shortly. 



With respect to the motion of camphor towards die light 



