No. Xn.] APPENDIX. 205 



for action imgratified " — a force contending with obstacles, ready to act, 

 but not actually in action. 



The effects of tension may arise from a variety of causes, since it is 

 always produced when a new attraction is offered, which is counteracted by 

 a previously existing one. The electrical machine is the instrument by 

 which the greatest amount of tension is procurable. 



" The electrical tension generated by the machine arises from friction. 

 Friction, we shall hereafter show, is the result of force — ^f orce of some new 

 attractions. Friction, therefore, being derived primarily from attraction, 

 may counterbalance other attractions. In the electrifying machine and all 

 its analogues, where friction is exerted, there must be more or less ten- 

 dency to the destruction of the attractions. This tendency may be called 

 the desire for action, which is opposed by the attraction of cohesion ; this 

 desire for action is the tension." — P. 20. 



The theory of the electrical machine, and the phenomena commonly 

 said to arise from itid/uction of electricity, having been disposed of, our 

 author passes to a stupendous chain of phenomena, depending on the same 

 principle, of which we extract his explanation at some length : — 



" Having considered galvanic tension and f rictional tension, we have 

 next to describe lightning tension. The tension in this case is evidenced 

 between the surface of the earth on the one hand, and a cloud on the other, 

 the air being the imperfect conductor, at the surfaces of which the ends 

 of the tension are manifested; that is, one surface is positive, and the 

 other negative. The attraction which is the source of the tension, perhaps 

 present facts have hardly sufficiently proved. Still, when we perceive that 

 a rapid formation of clouds, of rain, and even hail, always accompanies 

 the phenomena, we shall not probably much err in attributing the effects 

 to the sudden attraction of aqueous vapour into cloud, rain, or hail. This 

 new attraction, acting upon the air as a non-conductor, causes a polarity 

 of that air, which is communicated between the surface of the cloud on the 

 one hand, and that of the earth on the other. Such a mode of the forma- 

 tion of a thunder-cloud agrees well with the natural phenomena. It is 

 appai-ent, from such a cause, that the entire surface of the cloud on the one 

 hand, and the surface of the eai-th opposed to it on the other, would be in a 

 state of high tension — a result which is in perfect accordajice with the fact. 



" The electrical power capable of being exerted between the cloud and 

 the earth is enormous. The intensity is so great, that it is capable of 

 passing through a thousand feet, or more, of air during the discharge. 

 The quantity is equally vast ; for the cloud and tension may be exerted 

 over very many square miles, occasionally even for 100 square miles. The 

 electrical effects being equal to the intensity (1000 feet of aii") multiplied 

 by the quantity (100 square miles), will produce a result which, when com- 

 pared with the power of an enormous Leyden jar, the intensity of which 

 (half -inch air) is multiplied by 100 square feet, shows so wide a difference 

 that a comparison can scarcely be made. This diffei'ence, while it shows 

 to the presumptuous philosopher the vanity and impossibility of attempting 

 to produce this great phenomenon of nature, yet it amply demonstrates to 

 those who undervalue scientific investigation how, by paying attention to 

 minute experiments in the laboratory, the operations of nature may be 

 explained and comprehended. The lightning-cloud almost invariably 

 appears when rain follows long-continued easterly winds, which render 



