74 



On Lightning Rods. 



Vol. III. 



some erroneous opinions respecting' their in- 

 tention and mode of operation; to encourage 

 my readers to avail themselves of the yirotec- 

 tion uliich they aflbrd ; and to fnrnit^h a few- 

 plain, practical directions how to have them 

 constructed. To the electrician this may 

 seem unnecessary ; but the g:reat mass of 

 ag-ricultural readers may (without any dis- 

 paragement,) be said to have very little ac- 

 quaintance with the subject. Thev have not 

 had an opportunity to study electricity as a 

 science. As I am writing- for this class, I 

 shall endeavor to be accurate rather than 

 scientific, and practical rather than tlieo- 

 retical. 



Every one knows that the object of a light- 

 ning' rod is to protect the building from injury 

 by lightning; but every one does not know 

 how thdt protection is afforded, or what con- 

 ditions are necessary to secure it. For in- 

 stance, many persons believe that the rod is 

 intended to -present an attractive point for 

 the /ightning to strike to, and then to convey 

 it harmlessly to the ground. 'J'his belief is 

 altogether erroneous; and more, it is injuri- 

 ous ; and why ? because those persons very 

 naturally suppose, that if the rod has power to 

 draw the stroke at all, it will sometimes bring 

 it to the building, when it would otherwise 

 have passed to a distance, and thus do more 

 } arm than good. If the premises were true, 

 tlje conclusion would also be true, and the 

 objection valid. Many are discouraged from 

 putting up rods by this view of the subject. 

 But so far is the rod from presenting a point 

 for the lightning to strike to, that I helieve it 

 irnpossihle for it to do so when the rod is 

 properly constructed in every particidar. 

 J'his is undoubtedly true under all ordinary 

 circumstances. I hope my readers will tor- 

 liear to call this language presumptuous. 

 The phenomena of electricity, like all the 

 other operations of nature, are governed bv 

 certain and fixed laws. When these laws are 



Pig. II. 



once ascertained, we can speak with as much 

 confidence, and with as little presumption, of 

 the attraction of electricity, wliicb cauae^ it 



to pass from the clouds to the earth, as we 

 can of the attraction (f isruvitution, which 

 "draws the stone unerring to the ground." 

 It has been satiatactorily ascertained, 



1. That when a metallic ball is presented 

 to an electrified body, as in fig. 11, it will 

 receive a spark, accompanied with an explo- 

 sion, and the body will be found to have lost 

 more or less of its electricity. The distance 

 to which the spark will pass, is called the 

 striking distance, and varies with the inten- 

 sity of the charge, and a variety of other cir- 

 cumstances which need not be enumerated 

 here. 



2. That when a metallic point is used in- 

 stead of a ball, as in tig. 12, no spark or explo- 



Fi?. 12. 

 sion will be perceived ; hut tlie electricity of 

 the electrifipd body will be discharged — even 

 more completely t!i;m in liie fijrmer case — 

 v\hile tlip point is rtt a uii:c!i grevtor distance 

 than the ball was in the tonner experiment. 

 If this experiment Le made in the dark, a 

 small star of electrical light may be perceived 

 on the point. 



3. That when the ball nnd point are btith 

 presented to the flectrified body at the same 

 t me, as- in fig. 18, its electricity will be 



Fig. 13. 



silently discharg-ed, a.s in the second experi 

 meat, long before Uie ball cornea witliia its 



