252 PROCEEDINGS OF THE AMERICAN ACADEMY 



of Franklin's theory drawn from this experiment, have been contented 

 with showing that the direction of motion is not always in correspond- 

 ence with a current passing from the positive to the negative arm, and 

 that trifling modifications in the experiment are sufficient to change the 

 direction of the motion. I have been able to satisfy myself that the 

 motion is not produced either by the electrical current (a supposition 

 which probably few would adopt), or by the current of air which ac- 

 companies the passage of the electricity ; and that, therefore, the di- 

 rection of the motion, even if it were always the same, would justify 

 no inference in regard to the direction of the electrical current. This 

 motion is another instance of that numerous class which depends on 

 alternate attractions and repulsions. This we can show by the follow- 

 ing experiments : — 1. By substituting a ball for the pointed extremity 

 of the discharging-wire, the motion continues and its velocity is in- 

 creased. 2. If the wheel is insulated, no motion can be produced 

 either with a pointed or blunt discharging-rod. 



" Where the wheel is exposed between the arms of the universal 

 discharger to a similar action on both sides, the direction of the motion 

 will be determined by the relative tension of the two arms, and this 

 relative tension will depend on the shape and mass of the metal connect- 

 ed with the prime conductor, as compared with the shape and mass of 

 the metal connected with the rubber. Ordinarily, the negative mass is 

 small, imperfectly insulated, and not communicating freely with the 

 inside of the rubber, where the electricity is generated. These remarks 

 apply with equal force to all those test experiments analogous to the 

 one I have particularly discussed." 



Mr. J. H. Abbot communicated some additional electrical 

 facts, among which he described the effects produced by light- 

 ning upon a savin or red-cedar tree, the Juniprrus Virgini- 

 ana of botanists, in the eastern part of Beverly, in the summer 

 of the year 1845. The course of the lightning could be 

 traced by displaced stones, and several discontinuous furrows 

 radiating from the trunk of the tree, one of which extended 

 to the distance of two or three rods, while the tree itself was 

 uninjured. These effects Mr. Abbot contrasted with the ef- 

 fects produced by lightning, during the same summer, upon a 

 large chestnut-tree, in the northern part of Mason, New Hamp- 

 shire, a large part of which was shivered into fragments, and 



