248 



THE WORLD'S ADVANCE 



LIGHTNING PROTECTION. 



(9) C. T. P., New York City, asks: 



Q. i. What kind of a ground connection 

 as a protection against lightning can I have 

 in an apartment house where no space is avail- 

 able for above purpose? 



A. i. This all depends on the facilities at 

 hand. The Fire Underwriters usually require 

 a No. 4 copper ground running from the 

 point outside of the house where the ground 

 switch is located to disconnect the aerial from 

 the instruments to a good earth or pipe 

 ground outside of the house. Is it impossible 

 for you to drive a i in. iron pipe in the ground 

 directly below the point of entrance of your 

 lead-in and to run a No. 4 copper wire to 

 this pipe? If your aerial is not large, the 

 inspector may give you permission to connect 

 your ground wire to a radiator inside of the 

 house. This method has been used where 

 there is a radiator in the room near the lead- 

 in, and it has been found to work satisfac- 

 torily, although it must by necessity add an 

 element of danger if the ground wire runs 

 in an exposed position or for any consider- 

 able distance within the house. 



Q. 2 . What detector is known to be the 

 most sensitive at the present time? 



A. 2. The audion in some of its more com- 

 plex forms is unquestionably the most sen- 

 sitive detector yet known. By using three 

 audions very extensive amplifications are ob- 

 tained. 



STORAGE BATTERIES. 



(10) A. J. M., Wausaukee, Wis., asks: 

 Q. i. How to connect a storage battery 

 with the magneto generator on a Ford auto- 

 mobile ? 



A. i. A storage battery requires a direct 

 current, and, since the Ford generator gives 

 alternating currents, the project is impossible. 

 You will have to substitute or add a direct- 

 current magneto. A number of firms ^are 

 making specialties for Ford cars, and it might 

 be worth your while to address the Gray & 

 Davis Co., Amesbury, Mass., or some of their 

 agents, or the General Electric Co., at their 

 Milwaukee office, in the Public Service Build- 

 ing. Electric auto-starters, involving a motor 

 and storage batteries, are offered that will ex- 

 actly fit the space available, and give a very 

 satisfactory equipment, the expense being $75. 



INDUCTION MOTOR PROBLEM. 



(n) M. E. P., Wrangell, Alaska, asks: 

 Q. j _\yhat is likely to be the reason that 

 an induction motor modified from an old 

 direct-current Westinghouse fan motor will 

 not operate? A new 2O-slot laminated stator 

 was made, and the original armature was 

 fitted with eleven No. 4 copper wires, sol- 

 dered, though imperfectly, to copper end- 

 rings. 



A. i. The use of 20 slots is permissible, 

 though in keeping with the number required 

 for the running coils of Watson's motor, to 



which you referred, you would have had but 

 16. You did not state how the winding 

 was arranged, but it should be as follows: 

 A coil filling slots 3 and 4; a concentric coil 

 in series with this filling slots 2 and 5; a 

 coil concentric with these and occupying only 

 one-half of slots i and 6. This group would 

 constitute the winding for one of the four 

 poles. Similarly, there will be full coils in 

 slots 8 and 9, 7 and 10, and a half coil in 6 

 and ii ; a third group will be^ in slots 13-14. 

 12-15 and 11-16, the fourth in 18-19, 17-20 

 and 16-1. As the inner coils embrace very 

 little iron, it would have been an improve- 

 ment to have had the four central teeth larger. 

 You should rebuild the rotor, using copper 

 rods long enough to extend through holes 

 drilled in the end rings, then head them over 

 and solder-sweat them in position. 



AERIAL. 



(12) C. W. S., Modesto, Cal., asks: 



Q. i. Would you consider an aerial for 

 wireless work well proportioned with the fol- 

 lowing dimensions: 125 feet long, with a 

 height of 100 feet at one end and 50 feet at 

 the other end, consisting of eight stranded 

 wires 30 inches apart? 



A. i. Yes, it would be satisfactory but 

 would have a wavelength of greater than 200 

 meters. 



Q. 2. How would you split this aerial in 

 order to use two leads so as to send or trans- 

 mit on part of it without exceeding the 200- 

 meter limit and yet do efficient work? 



A. 2. Any method of trying to split it will 

 prove unsatisfactory. If you desire to use 

 this aerial use as short a lead-in as possible 

 and put a condenser in series. This will not 

 be as efficient as having an aerial of the cor- 

 rect proportions to start with. 



THE DISCOVERY OF GUNPOWDER. 



(13) H. S. S., Cedar Rapids, Neb., asks: 

 Q. i. Was gunpowder discovered or in- 

 vented? 



A. I. That a mixture of sulphur, charcoal 

 and salt-peter would unite with explosive 

 force was certainly a discovery, and even the 

 determination of just what proportions of the 

 chemicals to use, in what forms, etc., would 

 also properly be termed discoveries, but pro- 

 cesses for manufacturing the article might be 

 termed inventions. Discoveries are not pat- 

 entable, but a manufactured article or inven- 

 tion, resulting from discovery, is patentable. 

 Certain processes for making gunpowder, per- 

 haps the only ones for particular kinds, may 

 be patented. 



No questions will be answered by mail un- 

 less they are accompanied by the fee of fifty 

 cents. This fee is charged to partly defray 

 the time involved in answering inquiries. 



