Popular Scie7ice Monthly 



156 



in Fig. 1. These serve as insulators. 



In Fig. 3 is shown how the above de- 

 scribed Tesla coil with a few alterations 

 can be converted into an Oudin coil. 

 The three small blocks A are used to 

 support the secondary. 



The hook-up for a Tesla coil is shown 

 in Fig. 4, and the abbreviations used are 

 as follows: R. S. G., rotary spark gap; 

 C and C, condensers; S. G., safety gap. 



Various experiments are shown in Figs. 

 5, 6 and 7. The two wires in Fig. 5 are 

 connected with the binding posts of the 

 secondary and are left to project verti- 

 cally in the air. Long streamers wave 

 about, producing a weird effect. 



The experiment in Fig. 6 produces a 

 cone of light. Two wire hoops, one 12 in. 

 in diameter and the other 3 in. in diam- 

 eter, are connected with the secondary, 

 and the lead wires are so bent that the 

 hoops are separated 5 or 6 in. 



When a gap is made as shown in Fig. 7, 

 a spark 10 to 12 in. is obtained. Of 

 course all these experiments should be 

 made in the dark. 



If two metal disks about 1 in. in diam- 

 eter are provided and one attached to 

 each of the connection leads, a brilliant 

 flow of light will be produced from their 

 edges. For another experiment, suspend 

 two metal rods from the ceiling or other 

 support so that they will hang about 

 2 in. apart. Connect these to the leads. 

 Sparks will start at the bottom and run 

 to the top, making a ladder of light. 



When the coil is converted into an 

 Oudin coil the bottom binding post is 

 connected with the lower turn of the 

 primary; otherwise the connections are 

 the same as for the Tesla coil, as shown 

 in Fig. 4. A brass ball 2 in. in diameter. 

 Fig. 8, should be screwed on the top 

 binding post of the secondary in place of 

 the thumbnut. One of these may be 

 obtained from an iron bed. 



An interesting field for high frequency 

 experimenting is in connection with the 

 X-rays. The bulb, Fig. P, is connected 

 with the secondary leads of the Tesla 

 coil at A and B on the bulb. The wire 

 C is the vacuum regulator, and is oper- 

 ated by bending it over near A so a, 

 spark will jump while the tube is running. 

 Good X-ray photographs of the hand 

 or other objects may be made with this 

 apparatus. To take an X-ray photo- 



graph, load a plate holder with one plate 

 only, then expose it, holding your hand 

 or other object against the side of the 

 plate holder nearest the plate. The 

 X-rays penetrate the light-proof slide 

 with ease. The time of exposure can 

 only be determined by trial. A good 

 printing negative can be made by holding 

 the plate holder 5 in. from a 6-in. tube 

 and exposing it for 2 minutes. 



• 



An Electric Torch Made of Bichro- 

 mate Solution in a Bottle 



ONE of the most novel of the many 

 electric torches recently invented, 

 consists merely of a wide-mouthed bottle 

 having rods of zinc and carbon inserted 

 through a rubber cork. These rods pro- 

 ject down into the bottle for about one- 

 third of its depth. On top of the cork a 

 small electric lamp is mounted, similar 

 to those used in ordinary electric torches. 

 Connections are made between the lamp 

 and the zinc and carbon rods. 



A mixture of water, bichromate of 

 potash, and sulphuric acid is put into the 

 bottle, and stands at a level of about 1 

 in. below the end of the zinc and carbon 

 rods when the bottle is upright. When 

 the bottle is turned upside-down, it 

 becomes what is known as a bichromate 

 cell, a well-known type of cell for pro- 

 ducing small quantities of electricity for 

 electric bells and similar devices. The 

 electric current produced when the solu- 

 tion surrounds the zinc and carbon rods 

 is strong enough to light up the lamp, 

 and the apparatus becomes an electric 

 torch. The cork of the bottle must, of 

 course, be made perfectly water-tight. 



Square bottles with large round mouths, 

 such as are used for pickles and similar 

 products, are very suitable for these 

 torches, as they can be laid down on their 

 sides when light is required. 



Lacing Belts Through Eyeleted Holes 

 in the Leather 



The life of a belt may be lengthened 

 considerably, if instead of the customary 

 slits in the belt, eyelets obtained from 

 old shoes are substituted through which 

 to pass the thong in lacing. These will 

 prevent the thong from tearing out under 

 the strain when drawn tight. 



