376 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



cessant quivering motion, so rapid that it will be impossi- 

 ble to follow the course of a particle. The most convenient 

 substance is kaolin, which, when shaken up with pure water 

 to make a milky liquid, shows the motion in great perfec- 

 tion. This motion, he states, is not due, as has been suggest- 

 ed, to rays of light or heat ; nor is it connected with the 

 shape of the particles; nor yet is it due, as Tyndall has 

 supposed, to surface-tension. Pure water exhibits peclesis in 

 the highest perfection, even the air, and carbonic acid usu- 

 ally dissolved in it, producing a perceptible difference; by 

 the sli<xhest addition of sulphuric acid the movement is al- 

 most entirely destroyed, and, as a general rule, by all salts 

 and soluble substances. The exceptions are, pure caustic 

 ammonia (but not its compounds), boracic acid, and silicate 

 of soda gum arabic even possessing the power of increas- 

 ing the motions. The Professor draws a parallel between 

 Faraday's experiments in the production of electricity by 

 the Armstrong electrical boiler and his own in pedesis, and 

 finds that those substances which prevent or modify the pro- 

 duction of electricity operate in the same manner in prevent- 

 ing or modifying pedesis; and hence he considers it as an 

 electrical phenomenon. In attempting to explain the exact 

 modus operandi, we can only speculate that the action upon 

 minute irregular fragments will never be exactly equal all 

 round. In order that a particle shall rest motionless in a 

 non-conducting fluid or poorly conducting one, as pure water 

 is, it must be in exact equal and chemical electric relation 

 to the fluid on all sides. It is almost infinitely improbable 

 that this should happen, and a condition of unstable equilib- 

 rium within limits is the result. The Professor concludes by 

 pointing out that there is probably a close connection be- 

 tween pedesis and the phenomena of osmose (London Quar- 

 terly Journal of Science, April, 1878). 



Since the publication of the preceding investigations, 

 Professor Jevons, in making some experiments with a view 

 of testing the opinion of Professor Barrett and some other 

 physicists, that pedesis was due to surface-tension, and who 

 have suggested soap as a critical substance, inasmuch as it 

 reduces the tension of water, in which it is dissolved, with- 

 out much affecting (as is said) its electric conductibility, 

 found that, with a solution of common soap, the pedetic mo- 



