152 



SCIENTIFIC AGRICULTURE. 



January, 1922. 



under such conditions, yet they were smal- 

 ler and less violent than if the connections 

 were not made. The preponderance of 

 scientific indications and likewise the re- 

 sults of practice, point to the advisability 

 of having all metals lying near the conduc- 

 tor connected up to the system and under 

 certain conditions also grounded. 



Herein lies one of the weak points of all 

 iron rods and of stiff copper rods. It is 

 difficult to make sufficient electrical con- 

 tact at junctions of stiff cables either with 

 metal objects or with other parts of the 

 cable itself. In a number of cases w^ere 

 lip-htning rods have failed the conductors 

 at^ the junctions have been found burii"d 

 up by the heat generated through resist- 

 ance at the poor connections. 



One other feature remains to be dis- 

 cussed, viz., type of cable. In the early 

 '80 's several eminent scientists demon- 

 strated that when a current starts tbroug/i 

 a conductor it begins on the outside and 

 gradually penetrates inward, and it also 

 stops first at the surface. In 1885 Heave- 

 side demonstrated that rapidly alternating 

 currents confine themselves to the surface 

 of conductors— "skin effect," and physi- 

 cists are pretty generally agreed that in 

 the lightning conductor when struck the 

 same condition prevails because, with't;ie 

 instantaneous duration- of the flash, there 

 is not time for the current to penetrate 

 deeply: and that from the rapid rise of 

 the current self-induction must be grea,t. 

 Lodge experimenting with wire vs. tape 

 found that the latter has much less self- 

 indu'-tion than tjie former and that "thin 

 ribbon shows a distinct advantage over 

 round rod." However realizing tliat thin 

 ribbon was difficult to handle and possi- 

 bly not dural)le, he advised making the 

 cables of moderately small wires, in order 

 to secure more surface and thus reduce the 

 self induction with its liability to side 

 flash. This suggestion has been widely 

 adopted. F'ollowing along the same liiu-, 

 a flat woven cable )ias now been developed 

 in which every wire comes to both surfaces 

 and which consequently has about twice 

 as much exposed surface as round cables 

 containing the same amount of material. 

 By official test within the last year the 

 flat cable has been found to have less 

 self-induction, less resistance, and conse- 



quently to develop less heat and offer 

 greater capacity than a number of heavier 

 round cables against w>iich it was tested. 

 An equally important feature of flat 

 cables is that on account of their foi-m 

 they lend themselves to better connections 

 both mechanically and electrically than is 

 possible with round cables, no matter 

 whether those connections be with metal- 

 lic portions of the structure or between 

 different parts of the cable and equip- 

 ment. The trend in the future must nat- 

 urally be toward t^e more general adop- 

 tion "of this better type of cable. 



The 0. A.C. data prove that in many 

 cases strokes are actually prevented, but 

 not in all. And Lodge in his experiments 

 showed that it is impossible to prevent 

 them all. Sometimes a cloud charges up 

 gradually and sometimes suddenly. In the 

 former case prevention is possible by per- 

 mitting the earth charge, or at least part 

 of it, to gradually leak off points and thus 

 quietly make it way to and neutralize that 

 in the cloud, sufficiently to reduce the po- 

 tential below bursting tension, but in tjie 

 latter there is not time for leakage to occur 

 and a flash follows, and if toward a build- 

 ing a well installed system of protection 

 will carry it off without damage in nearly 

 all cases. 



With science and experience pointing 

 the way in the matters of material' type 

 of cable, handling metallic bodies, design- 

 ing system for different buildings, and 

 lastly methods of installation, and with 

 the Lightning Rod Act providing Govern- 

 ment regulation to insure that the known 

 standards shall be lived up to by all, there 

 is reason to believe t,he general efficiency 

 of lightning rods henceforth installed in 

 Ontario can be raised to nearly 100 p.c. 



SHELTER-BELTS AND SOIL 

 FERTILITY. 



A blanket of four or five inches of snow 

 over a prairie farm during winter and 

 until early spring means a large amount 

 of moisture for the soil. Tlie problem is 

 to keep it there and not have it blown 

 away by high winds. This is wjiere shelter 

 belts on the farm prove their value hy 

 ])i'eventing drifting and thus retaining 

 moisture and fertility. 



