250 STATE BOAED OF AGKICULTURE. 



is the opposite of that state of excitement following friction, chemical action, 

 etc,, which is called dynamic electricity, or electricity in motion. Strictly 

 speaking, all quiescent electricity is static, and all electricity in motion, from 

 whatever source, is dynamic.*' 



Prof. Henry supports this definition in his published Avorks, and speaking of 

 electricity, says: ''The phenomena are of two classes, namely, statical, or 

 those of attraction and repulsion, in which the electricity is at rest, and dynam- 

 ical, or those in which the redundant electricity of one portion of space is pre- 

 cipitated into that of another in which there is a deficiency." 



With the aboYC definitions before him the intelligent reader can readily per- 

 ceive which kind of electricity is spoken of in the quotations made in my article. 

 I will simply refer to the authorities cited ami the language employed character- 

 izing the electricity spoken of. Prof. Silliman, an "excited body;" Wells' 

 Natural Philosoijhy, "a conducting body ;" Drapers Chemistry, ''a conducting 

 body;" Olmstead's Philosophy, "electrical conductors;" Memoirs d' Academic, 

 "the best conductors;" General Science, "electricity, passing," and "metals 

 conducting electricity ;" Chambers' Cyclopedia, " outer surf ace of conductors;" 

 Cycloj^edia Britannica, "conducting surfaces;" Experiments of Coulomb, 

 "conductors cai'ry the electricity upon their surface ;" and the American Cyclo- 

 pedia, "capacity of metals for conduction." Are these authorities speaking of 

 quiescent electricity, — electricity at rest, — or are they speaking of electricity in 

 motion ? 



The doctor's question with regard to the effect of electricity upon gold leaf 

 loses much of its force when we consider that instances have been known where 

 strips of copper two inches in width and one-sixteenth of an inch in thickness 

 have been similarly affected by a stroke of atmospheric electricity. Indeed, it 

 is not claimed by any that surface, without substance, is sufficient. Prof. 

 Henry says that "if the charge be large and the conductor small, it will in 

 some cases convert into an impalpable powder, or vapor, the solid particles." 



And noAV for some authority having a direct bearing upon the question at 

 issue. Prof. Henry, in an exhaustive article on atmospheric (not static) elec- 

 tricity, saj-s : "Because. electricity in a state of rest is found distributed at the 

 surface of a body, it was imm,ediately assumed, Avithout examination, that elec- 

 tricity in motion passed along the surface ; but this conclusion was supposed to 

 be disproved by the fact that the conducting power of a wire for galvanic elec- 

 tricity is in proportion to the area of a cross section, from which it follows that 

 this kind of electricity pervades the Avhole mass of the conductor. But galvanic 

 electricity differs from common electricity, apparently in the exertion of a much 

 less energetic repulsion, and in a greater quantity developed in a given time. 

 The deduction, therefore, from the experiments with galvanism can scarcely be 

 considered as conclusive in regard to frictional electricity. To settle this point 

 the author of this paper (Prof. Henry) instituted a f.eries of experiments, 

 which conclusively proved the tendency of electricity of high tension, that is of 

 great repulsive energy, to pass along the surface." 



And speaking particularly of the construction of lightning-rods, the same 

 author makes use of the following language: "Electricity, as we have seen, 

 tends to pass at the surface of a conductor of a sufficient size ; " and "the only 

 proper way of diminishing the resistance to conduction in a cylinder of metal of 

 argiven capacity, is to mould it into the form of a hollow cylinder; a gas-pipe, 

 for example, will offer less resistance to conduction than the same weight of 

 metal in the form of a solid cylinder." Fearing that the doctor might call 



