;oS 



NA TORE 



(July 30, 1908 



ings, and consequent shorts between adjacent turns ; (2) to 

 prevent excessive voltage between the wires and ground, 

 causing breakdown to ground over insulators. To avoid 

 (i), recourse may be had to high insulation, but this is 

 not always practicable, and generally vi'ell-insulated 

 choking coils are placed between the line and the terminal 

 apparatus. If these break down they may be easily taken 

 out and repaired. For (2), " lightning arresters " must be 

 used. The essentials of such an arrester are that it must 

 form an easier path to earth than the insulation resistance 

 of the transmission line or other parts of the apparatus, 

 and yet it must hold back the line voltage. There must, in 

 addition, be some device for suppressing the arc which 

 accompanies the discharge. 



One of the earliest forms of arrester was the horn type 

 (Fig. 1). This consists of two wires, one connected to 

 line and the other to earth. Each is bent at an acute 

 angle, so that they diverge from one another vertically 

 upwards. Their distance apart at the lowest point must 

 be adjusted so that no arc will occur for small increments 

 of norma! line voltage, but if the potential of the line con- 

 nected wire rises considerably, an arc is formed. This 

 arc rises, increasing in length, and is finally ruptured. 



certain electrolytes a non-conducting film is formed on the 

 surface of the metal. This film can withstand a pressure 

 of about 400 volts. At higher potentials it is punctured 

 with a series of small holes, and the cell becomes conduct- 

 ing. When the excess voltage is removed the non-conduct- 

 ing film re-forms. By building up a number of such cells 

 in series they may be made to withstand any desired 

 voltage. Such a series is contained in a cylindrical earthen- 

 ware vessel, the number depending on the normal line 

 voltage, and is connected between line and earth (Fig. 2). 

 It is usual to have a gap between line and electrolytic 

 unit. For voltages not exceeding 13,500 volts, a non- 

 arcing metal-cylinder gap may be used ; for larger voltages 

 one of the horn type is usual. Such arresters have been 

 adapted successfully to lines with voltages varying from 

 4000 to 60,000 volts. 



'THE ROV.4L IS'SiTITUTE OF PUBLIC 



HEALTH. 



'T'HE annual congress of the Royal Institute of Public. 



Health was held at Buxton from July 18-24. Among 

 the many and varied subjects which were discussed, the 



Fig. 2. — General view, 6o,ooo.volt lightning arresters. 



.■\n objection to this form of arrester is the length of tiine 

 elapsing between formation of arc and its rupture, for 

 during this time the system is earthed. It is usual to 

 place a high resistance in series with this arrester so that 

 the current to earth from the line is diminished, but this 

 will retard the static discharge. Owing to fusion of the 

 metal at the lowest point where arcing occurs, it needs 

 constant re-adjustment. .An improved form is in use with 

 an auxiliary gap and adjustable platinum point. 



The " non-arcing multi-gap arrester " depends on the 

 power certain metals have of suppressing an alternating 

 arc. A number of cylinders of suitable metal are placed 

 between line and earth. The cylinders are separated by 

 gaps of I /32-inch. They allow escape of the static charge, 

 but no arcing occurs. These have proved most successful 

 on low-voltage systems (2000 volts). 



On the Continent, an arrester consisting of jets of water 

 playing upon the line has been used. The chief objection 

 to this is that it allows leakage of current from line to 

 earth. The latest type of protecting device is the " electro- 

 lytic arrester." If aluminium electrodes are placed in 



NO. 2022, VOL. 7S' 



following papers aroused considerable interest and dis- 

 cussion : — 



.Sir James Crichton-Browne took for his presidential 

 address to the preventive medicine section " Parsimony in 

 Nutrition." He did not concern himself with any par- 

 ticular dietetic system, but considered the general dietetic 

 tendency towards abstemiousness which exists at the pre- 

 sent day. Detailed reference was made to the dietary 

 standards of Profs. Voit, of Munich, and Atwater, of the 

 United .States. These standards have been since found to 

 be too high. .Xn .American, Mr. Horace Fletcher, showed 

 that by careful and thorough mastication and insalivation 

 the bodily needs are not only satisfied by a smaller amount 

 of food, but the tone of the body is improved. Prof. 

 Chittenden's careful researches on the subject led him to 

 conclude that half the amount of proteids formerly con- 

 sidered necessary are quite sufficient. It was pointed out 

 that before our dietetic svstem was revised on any such 

 lines, it was essential to consider other facts. Concomitant 

 with the proteid-consuming habits of the western races 

 there had been a development of increased precision in 



