WEBVTT 1 00:00:00.800 --> 00:00:05.440 Section thirty one of the Science History of the Universe, 2 00:00:05.599 --> 00:00:10.439 Volume three. This is a LibriVox recording. All LibriVox recordings 3 00:00:10.480 --> 00:00:14.160 are in the public domain. For more information or to volunteer, 4 00:00:14.359 --> 00:00:20.920 please visit LibriVox dot org. Recording by Emelia Chesley, The 5 00:00:20.960 --> 00:00:25.359 Science History of the Universe, Volume three, edited by Francis 6 00:00:25.440 --> 00:00:35.600 rold Wheeler. Electricity, Chapter eleven Wireless Telegraphy, Part one. Professor 7 00:00:35.640 --> 00:00:38.600 Henry of Princeton University was the first to show the 8 00:00:38.640 --> 00:00:42.640 oscillatory character of the discharge of a Leyden jar. This 9 00:00:42.799 --> 00:00:45.240 single loud spark, which to the eye seems to pass 10 00:00:45.280 --> 00:00:48.000 in one direction across the gap, is really a quick 11 00:00:48.039 --> 00:00:51.600 succession of current surges, first one way and then the other, 12 00:00:52.079 --> 00:00:56.280 and has its mechanical analogy in the pendulum at the outset. 13 00:00:56.399 --> 00:00:59.320 It may be well to analyze this spark discharge, as 14 00:00:59.320 --> 00:01:01.520 it is still the most mos prominent means of radiating 15 00:01:01.600 --> 00:01:06.040 the electric waves used to transmit signals. Suppose this pendulum 16 00:01:06.040 --> 00:01:09.599 analogy of the spark discharge between two spheres be taken, 17 00:01:09.959 --> 00:01:13.200 and the similarity of the two actions noted. If a 18 00:01:13.239 --> 00:01:16.239 heavy pendulum be drawn back by means of a light fiber, 19 00:01:16.680 --> 00:01:19.200 it will finally strain the fiber to such an extent 20 00:01:19.280 --> 00:01:22.599 as to cause it to break. The pendulum, being suddenly released, 21 00:01:22.640 --> 00:01:26.560 gradually acquires motion, which is accelerated until its lowest position 22 00:01:26.680 --> 00:01:29.319 is reached, after which it is retarded just as it 23 00:01:29.680 --> 00:01:32.680 was accelerated, and stops at about the same height at 24 00:01:32.719 --> 00:01:36.079 which it started. The process is then repeated, but in 25 00:01:36.120 --> 00:01:39.519 the opposite direction. Now compare the action on the two 26 00:01:39.719 --> 00:01:43.959 charged spheres. The pressure in the dielectric surrounding the spheres 27 00:01:44.000 --> 00:01:46.920 is gradually raised until it suddenly gives way, there being 28 00:01:46.920 --> 00:01:49.799 a flow of current from the positive to the negative sphere, 29 00:01:50.200 --> 00:01:53.599 which current gradually increases and is greatest at the instant 30 00:01:53.640 --> 00:01:56.879 when bold dielectrics are at the same potential, just as 31 00:01:56.920 --> 00:01:59.920 the motion of the pendulum was greatest at its lowest position. 32 00:02:00.680 --> 00:02:03.560 The current then begins to decrease and finally stops when 33 00:02:03.560 --> 00:02:06.400 the dielectric is again strained to about the same potential 34 00:02:06.439 --> 00:02:09.960 it had at first, but reversed indirection. The current then 35 00:02:10.000 --> 00:02:14.960 starts back again, just as the pendulum again required motion. Now, 36 00:02:15.039 --> 00:02:17.120 let it be considered what goes on in the space 37 00:02:17.159 --> 00:02:20.479 surrounding this action. A current is always surrounded by a 38 00:02:20.520 --> 00:02:23.800 field of magnetic force, which field is proportional to the 39 00:02:23.840 --> 00:02:26.639 strength of the current. As this current between the two 40 00:02:26.680 --> 00:02:31.120 spheres increases, there is therefore sent out an increasing magnetic 41 00:02:31.159 --> 00:02:34.919 field which is radiated into space, reaching a maximum and 42 00:02:34.960 --> 00:02:38.879 again decreasing with the current. But while the current increases, 43 00:02:39.039 --> 00:02:43.240 the electrostatic strain about the sphere decreases, thus sending out 44 00:02:43.280 --> 00:02:47.560 an electrostatic wave, which again increases as the current decreases. 45 00:02:48.199 --> 00:02:51.000 It will thus be seen that as these surges take place, 46 00:02:51.319 --> 00:02:56.840 alternate electromagnetic and electrostatic waves are radiated into space. Why 47 00:02:56.879 --> 00:03:00.599 do not these surges keep on forever? Mainly because the 48 00:03:00.680 --> 00:03:04.240 current in its flow across the gap encounters a resistance, and, 49 00:03:04.360 --> 00:03:07.840 instead of converting all its energy into magnetic waves, loses 50 00:03:07.879 --> 00:03:11.520 a portion as heat at each surge. This corresponds to 51 00:03:11.560 --> 00:03:15.400 oscillating the pendulum in a liquid or viscous material, the 52 00:03:15.520 --> 00:03:19.439 energy of its motion soon being converted into heat. So 53 00:03:19.599 --> 00:03:22.439 much for the creation of these waves, But how may 54 00:03:22.479 --> 00:03:25.960 their passage through space be detected? One way is by 55 00:03:26.000 --> 00:03:28.800 catching them on a wire. What is the manner of 56 00:03:28.840 --> 00:03:31.719 the catching? If a wire be placed so that it 57 00:03:31.759 --> 00:03:34.960 cuts the wave transversely to its line of motion, it 58 00:03:35.039 --> 00:03:37.759 is clear that the moving magnetic wave will induce in 59 00:03:37.800 --> 00:03:42.120 it an electromotive force. As these waves follow in rapid succession, 60 00:03:42.240 --> 00:03:45.439 a series of alternating electromotive forces is set up in 61 00:03:45.479 --> 00:03:50.759 the wire. These oscillatory currents are sometimes called jigs. How 62 00:03:50.840 --> 00:03:53.759 these jig currents make their presence known varies with the 63 00:03:53.800 --> 00:03:58.879 style of wave detector used Before entering upon the history 64 00:03:58.879 --> 00:04:02.759 of this spark telegray, as the Germans call it, it 65 00:04:02.840 --> 00:04:05.479 may be well to review some of the experiments which 66 00:04:05.520 --> 00:04:10.319 preceded this system. In eighteen thirty eight, Professor Joseph Henry 67 00:04:10.319 --> 00:04:14.319 of Princeton, making with an electrical machine and leydingjar a 68 00:04:14.400 --> 00:04:16.879 one inch spark in the top room of his residence, 69 00:04:17.279 --> 00:04:20.560 set up induced currents in the cellar of the same building. 70 00:04:21.000 --> 00:04:24.920 Professor Morse, however, was probably the first to successfully transmit 71 00:04:25.040 --> 00:04:29.720 signals without wire. On December sixteenth, eighteen forty two, he 72 00:04:29.800 --> 00:04:33.079 sent a wireless telegram across a canal eighty feet wide, 73 00:04:33.439 --> 00:04:37.319 and in November eighteen forty four, L. D. Gale, acting 74 00:04:37.399 --> 00:04:41.199 under instructions from Professor Morse, made wireless signals across the 75 00:04:41.199 --> 00:04:44.720 Susquehanna River at Havre de Grace, a distance of nearly 76 00:04:44.800 --> 00:04:48.600 one mile. In the latter experiment, mister Gale used as 77 00:04:48.639 --> 00:04:50.920 a source of energy six pairs of plates in the 78 00:04:50.920 --> 00:04:54.360 form of a galvanic battery. He found that the best 79 00:04:54.399 --> 00:04:56.759 results were obtained when on each side of the river 80 00:04:57.160 --> 00:05:00.519 two plates were immersed near its bank and worked connected 81 00:05:00.560 --> 00:05:03.560 by an insulated wire stretched along each shore for a 82 00:05:03.600 --> 00:05:06.759 distance three times as great as that which measured either 83 00:05:06.839 --> 00:05:11.839 path of the crossing signals. A few years later, James Lindsay, 84 00:05:12.199 --> 00:05:16.199 a Scotchman, repeated Morse's experiments, but without knowing of them. 85 00:05:16.839 --> 00:05:19.319 In eighteen fifty nine he read a paper before the 86 00:05:19.319 --> 00:05:23.839 British Association on the subject of telegraphing without wires, and 87 00:05:23.920 --> 00:05:28.680 among his hearers were Faraday and Lord Kelvin. A method 88 00:05:28.720 --> 00:05:31.839 of signaling without wires by means of the inductive effect 89 00:05:32.040 --> 00:05:35.839 of two parallel circuits was successfully used by Sir William 90 00:05:35.879 --> 00:05:39.720 Preece in eighteen eighty two. The principle of this method 91 00:05:39.800 --> 00:05:42.639 is as follows. If two loops of wire are placed 92 00:05:42.680 --> 00:05:45.680 parallel to each other, and an intermittent current is passed 93 00:05:45.680 --> 00:05:48.759 through one of them, waves of magnetic flux are sent 94 00:05:48.839 --> 00:05:51.959 out portions of which thread the second loop, and by 95 00:05:52.000 --> 00:05:55.160 their fluctuations produce currents in it, which may be detected 96 00:05:55.160 --> 00:05:58.680 by a telephone or other device. The strength of such 97 00:05:58.720 --> 00:06:02.199 signals falls off very rapidly from the source, and such 98 00:06:02.199 --> 00:06:05.519 a system can only be made to operate over short distances. 99 00:06:06.759 --> 00:06:11.120 Priests constructed two parallel lines, one on the English coast 100 00:06:11.160 --> 00:06:13.639 and one on the Isle of Wight, the arrangement of 101 00:06:13.680 --> 00:06:17.000 which is shown in Fig. Forty eight. It will be 102 00:06:17.079 --> 00:06:20.279 seen that the loop from which the waves emana is 103 00:06:20.360 --> 00:06:24.959 formed by the line, wire and the Earth. The crowning achievement, however, 104 00:06:25.079 --> 00:06:27.959 was the work of Hertz, whose early death deprived the 105 00:06:27.959 --> 00:06:31.040 world of the aid of a most powerful brain. In 106 00:06:31.120 --> 00:06:34.120 eighteen eighty six, Hertz discovered that if a loop of 107 00:06:34.160 --> 00:06:36.839 wire having a small air gap left in it were 108 00:06:36.839 --> 00:06:39.199 placed at a distance from a spark discharge of a 109 00:06:39.279 --> 00:06:42.879 Leyden jar minute sparks would pass across the air gap 110 00:06:42.959 --> 00:06:46.120 of the loop, thus indicating the presence of electric waves. 111 00:06:46.639 --> 00:06:49.360 He subsequently made a very complete study of the behavior 112 00:06:49.399 --> 00:06:52.120 of these waves, and thus gave a tremendous impetus to 113 00:06:52.160 --> 00:06:56.279 the development of wireless telegraphy. Second to the work of 114 00:06:56.319 --> 00:06:59.279 Hertz is that of Sir Oliver Lodge, who, in eighteen 115 00:06:59.319 --> 00:07:01.839 eighty nine to descis discovered the effect of electrical waves 116 00:07:01.839 --> 00:07:04.480 on the breaking down of the electrical resistance of two 117 00:07:04.560 --> 00:07:08.720 knobs barely in contact, which discovery resulted in the first 118 00:07:08.800 --> 00:07:13.240 means used to detect the presence of electrical waves, the coherer. 119 00:07:14.720 --> 00:07:18.680 The development of wave detectors is an important chapter for 120 00:07:18.759 --> 00:07:22.279 these instruments. Professor Fleming has suggested the use of the 121 00:07:22.319 --> 00:07:26.319 word simoscope as a general term including all classes of 122 00:07:26.360 --> 00:07:29.920 wave detectors. A great number of these have been invented, 123 00:07:30.399 --> 00:07:33.600 but they may all be included under the following classes. 124 00:07:34.040 --> 00:07:40.920 One spark seymoscopes, two contact cymoscopes, three thermal cymoscopes, four 125 00:07:41.120 --> 00:07:49.399 magnetic cymoscopes, five electrolytic cymoscopes, six electrodynamic cymoscopes, and seven 126 00:07:49.879 --> 00:07:54.600 vacuum tube cymoscopes. The first cymoscope invented was that used 127 00:07:54.600 --> 00:07:58.120 by Hertz in his investigation of electrical waves, and belongs 128 00:07:58.120 --> 00:08:01.639 to the first class. Resisted merely of a ring broken 129 00:08:01.680 --> 00:08:04.079 at one point and arranged so that the gap might 130 00:08:04.120 --> 00:08:08.000 be adjusted by means of a micrometer screw. Tiny sparks 131 00:08:08.040 --> 00:08:11.839 across this gap indicated the presence of waves. Since the 132 00:08:11.879 --> 00:08:15.120 electromotive force required to produce a spark across even a 133 00:08:15.160 --> 00:08:18.240 small gap is very considerable. It will be obvious that 134 00:08:18.240 --> 00:08:21.079 such a detector could only operate at a short distance, 135 00:08:21.439 --> 00:08:24.040 and would therefore be useless for the purpose of signaling. 136 00:08:25.240 --> 00:08:29.040 The next invention, made in eighteen ninety was the Bramley 137 00:08:29.040 --> 00:08:32.960 Coherer Fig. Forty nine, which consisted of a small glass 138 00:08:33.000 --> 00:08:36.320 tube containing two metallic plugs and separated by a gap 139 00:08:36.480 --> 00:08:40.279 partially filled with metallic fillings. This is an example of 140 00:08:40.360 --> 00:08:44.120 the second class. The metallic fillings, when loosely packed, offer 141 00:08:44.200 --> 00:08:47.279 a very high resistance to the passage of current through them, 142 00:08:47.440 --> 00:08:50.440 but the presence of waves breaks down their contact resistance, 143 00:08:50.799 --> 00:08:54.080 which continues after the waves have ceased. In order to 144 00:08:54.159 --> 00:08:57.159 again restore their resistance, they must be tapped or shaken, 145 00:08:57.519 --> 00:09:01.559 an operation known as decoherence. It is obvious that such 146 00:09:01.600 --> 00:09:03.840 an apparatus may be used like a key in a 147 00:09:03.879 --> 00:09:07.919 telegraph circuit, a key operated by electrical waves, and may 148 00:09:07.960 --> 00:09:12.120 therefore be used to operate a telegraphic instrument. Such was 149 00:09:12.159 --> 00:09:15.559 the first device used. It was defective, however, in that 150 00:09:15.639 --> 00:09:18.960 it was necessary to tap it after each signal. Decoherence 151 00:09:19.039 --> 00:09:22.679 was not certain. It required frequent adjustment, and the result 152 00:09:22.720 --> 00:09:26.639 was often a confused lot of signals. Many arrangements of 153 00:09:26.720 --> 00:09:31.200 loose contacts were tried, and the coherer was improved by Marconi, Lodge, 154 00:09:31.240 --> 00:09:34.720 Braun and others. One of the principal troubles being the 155 00:09:34.759 --> 00:09:38.559 operation of decoherence. Most of the inventors sought to develop 156 00:09:38.600 --> 00:09:41.799 a coherer which could be self restoring, and a number 157 00:09:41.879 --> 00:09:44.799 of successful types were invented. One of these was the 158 00:09:44.879 --> 00:09:49.960 Hughes coherer, employing carbon granules placed between iron plugs. The 159 00:09:50.039 --> 00:09:53.840 most perfect and successful of all these is, however, that 160 00:09:53.960 --> 00:09:57.639 devised by Sir Oliver Lodge and doctor Muirhead and used 161 00:09:57.679 --> 00:10:01.240 in the Lodgemere Head system, as shown in figure fifty. 162 00:10:01.320 --> 00:10:04.519 It consists of a steel disk slightly separated from a 163 00:10:04.519 --> 00:10:07.720 globule of mercury by a film of oil. The disc 164 00:10:07.799 --> 00:10:11.679 being arranged to rotate slowly. The presence of waves breaks 165 00:10:11.720 --> 00:10:15.039 down the oil film and establishes contact with the mercury, 166 00:10:15.080 --> 00:10:18.320 which contact immediately breaks upon the cessation of the waves. 167 00:10:18.919 --> 00:10:22.200 A siphon recorder placed in the series with the symoscope 168 00:10:22.320 --> 00:10:25.279 is used to record the message. Although a number of 169 00:10:25.320 --> 00:10:28.399 forms of magnetic style of detector were devised. It was 170 00:10:28.440 --> 00:10:31.960 not until nineteen o two that a successful working apparatus 171 00:10:32.039 --> 00:10:35.440 was produced. For some time before that, it was known 172 00:10:35.519 --> 00:10:38.840 that the oscillating currents received would annull wholly or in part, 173 00:10:38.919 --> 00:10:42.519 the magnetic hysteresis of iron when passed through a coil 174 00:10:42.600 --> 00:10:47.320 surrounding the iron. Hysteresis acts like molecular friction, so that 175 00:10:47.360 --> 00:10:50.240 when a magnetizing current is passed through a coil surrounding 176 00:10:50.240 --> 00:10:54.080 an iron core, the magnetization does not increase and decrease 177 00:10:54.120 --> 00:10:56.679 with the current in the coil, but lags behind it. 178 00:10:57.200 --> 00:11:01.159 If another coil be placed around this core and the 179 00:11:01.200 --> 00:11:04.879 oscillating currents passed through it, this hysteresis will be suddenly 180 00:11:04.919 --> 00:11:08.000 removed and the magnetism in the core will suddenly change 181 00:11:08.039 --> 00:11:11.559 in value. This sudden change could be detected by a 182 00:11:11.600 --> 00:11:15.000 third coil surrounding the core and connected to a telephone receiver, 183 00:11:15.480 --> 00:11:19.360 resulting in a sudden click. This was the principle of 184 00:11:19.399 --> 00:11:23.159 which Marconi made use in his magnetic detector, and which 185 00:11:23.159 --> 00:11:26.600 he has used in his long distance experiments. The arrangement 186 00:11:26.720 --> 00:11:29.840 is shown in Fig. Eighteen. It consists of a band 187 00:11:29.879 --> 00:11:33.320 of iron wires passing through two coils, one carrying the 188 00:11:33.399 --> 00:11:36.840 jig currents and one connected to the telephone. The wires 189 00:11:36.840 --> 00:11:39.799 are magnetized by two permanent magnets, and as they move 190 00:11:39.960 --> 00:11:43.000 under that portion where the two poles meet, the magnetic 191 00:11:43.039 --> 00:11:47.240 flux in them undergoes a reversal. Which reversal, however, always 192 00:11:47.279 --> 00:11:50.320 takes place at the same point until the jig currents pass, 193 00:11:50.679 --> 00:11:54.120 when the flux is suddenly shifted backward, causing a sound 194 00:11:54.159 --> 00:11:58.159 in the telephone. These detectors have come into very general 195 00:11:58.240 --> 00:12:01.960 use on account of their convenience, sensitiveness, and adaptation to 196 00:12:02.080 --> 00:12:05.759 rapid signaling. In nineteen o one, doctor Lee de Forest 197 00:12:05.879 --> 00:12:09.240 patented a detector which depends for its operation on the 198 00:12:09.279 --> 00:12:13.279 disruption of the minute metallic bridges or trees, which form 199 00:12:13.399 --> 00:12:17.279 under suitable conditions between the electrodes of an electrolytic cell. 200 00:12:18.200 --> 00:12:22.519 The apparatus, called a responder, consists in a glass tube 201 00:12:22.559 --> 00:12:25.360 similar to that of a coherer, in which are fitted 202 00:12:25.360 --> 00:12:29.919 two electrodes, preferably of tin. The space between the electrodes, 203 00:12:30.039 --> 00:12:32.960 about one sixty fourth of an inch, is filled with 204 00:12:33.039 --> 00:12:36.799 a viscous semiconducting liquid such as glycerine, with a small 205 00:12:36.840 --> 00:12:40.399 admixture of water, together with some peroxide of lead as 206 00:12:40.399 --> 00:12:44.799 a depolarizer to prevent the excessive evolution of gas. When 207 00:12:44.840 --> 00:12:48.200 a cell of suitable voltage is connected across this responder, 208 00:12:48.720 --> 00:12:52.480 metallic trees or bridges are formed which make a path 209 00:12:52.519 --> 00:12:55.799 of low resistance. But upon the passage of the jig currents, 210 00:12:55.840 --> 00:12:59.120 these trees are broken down and the circuit broken, producing 211 00:12:59.159 --> 00:13:02.279 a sound in a telefe phone receiver. Immediately upon the 212 00:13:02.320 --> 00:13:06.679 cessation of the jig currents, however, these trees again establish themselves. 213 00:13:07.519 --> 00:13:11.759 Another very successful and extremely sensitive detector was invented by 214 00:13:11.840 --> 00:13:16.279 Fessenden and Friedland and consists of a small platinum cathode 215 00:13:16.279 --> 00:13:20.679 containing nitric acid with a minute anode of platinum wire 216 00:13:21.200 --> 00:13:25.519 one ten thousandth of an inch in diameter. This little 217 00:13:25.559 --> 00:13:28.840 electrolytic cell, when polarized to the critical point by being 218 00:13:28.840 --> 00:13:32.759 connected to a battery, is remarkably sensitive to jig currents. 219 00:13:33.200 --> 00:13:36.799 It has been employed by Festenden in his transatlantic experiments. 220 00:13:37.960 --> 00:13:41.799 Many other detectors have been developed which have operated successfully, 221 00:13:42.200 --> 00:13:45.799 but those described are used most generally. It would not 222 00:13:45.919 --> 00:13:48.879 be possible, in a few words, to give a comprehensive 223 00:13:48.919 --> 00:13:52.320 idea of the various systems in use, as many important 224 00:13:52.320 --> 00:13:54.840 improvements which have been made in the last ten years. 225 00:13:55.679 --> 00:13:59.159 Those systems which have attained commercial importance are the Marconi, 226 00:13:59.399 --> 00:14:02.720 the Festen d, the de Forest, the slaviy arco and 227 00:14:02.759 --> 00:14:06.440 the Lodgemere head. The greatest differences are usually found in 228 00:14:06.480 --> 00:14:11.200 the receiving apparatus. The first system used by Marconi employed 229 00:14:11.240 --> 00:14:14.480 the coherer as a wave detector and the room wharf 230 00:14:14.559 --> 00:14:18.000 coil to produce the sparks from which the waves were radiated. 231 00:14:18.679 --> 00:14:21.960 The diagrammatic arrangement of the sending and receiving apparatus is 232 00:14:22.000 --> 00:14:25.320 shown in Fig. Fifty two, T being the coherer and 233 00:14:25.759 --> 00:14:30.039 l the telegraphic relay. Experiments with this form of apparatus 234 00:14:30.039 --> 00:14:32.919 were first made in eighteen ninety six in England, where 235 00:14:32.960 --> 00:14:35.960 Marconi went to obtain the assistance of Sir William Priest. 236 00:14:37.039 --> 00:14:40.440 These experiments were so successful that trials were made during 237 00:14:40.440 --> 00:14:44.639 the next year, at each of which something new was learned, 238 00:14:44.639 --> 00:14:48.519 whereby the distance of transmission was increased. From some of 239 00:14:48.519 --> 00:14:51.200 these experiments, Marconi worked out the effect of the height 240 00:14:51.279 --> 00:14:55.039 of the antenna or aerial wire on the distance of transmission. 241 00:14:56.399 --> 00:15:00.399 In August eighteen ninety seven, Marconi organized a company known 242 00:15:00.440 --> 00:15:03.679 as the Wireless Telegraph and Signal Company with a capital 243 00:15:03.720 --> 00:15:08.679 of five million dollars. In June eighteen ninety seven, Marconi 244 00:15:08.720 --> 00:15:11.600 went to Rome, and, after having undertaken in this city 245 00:15:11.639 --> 00:15:15.279 at the instigation of the Minister of Marine several experiments 246 00:15:15.360 --> 00:15:18.000 from one floor to another with a conductor three yards 247 00:15:18.039 --> 00:15:22.240 in height, was invited by the Honorable Brin, Minister of Marine, 248 00:15:22.279 --> 00:15:25.360 to undertake in the presence of a select commission composed 249 00:15:25.399 --> 00:15:28.879 of officers who were specialists belonging to the Royal Marines, 250 00:15:29.200 --> 00:15:33.759 some fresh experiments. The place chosen was the Gulf of Spitzia. 251 00:15:34.360 --> 00:15:37.559 The experiments took place between the eleventh and eighteenth of 252 00:15:37.639 --> 00:15:42.080 July eighteen ninety seven. The apparatus made use of for 253 00:15:42.240 --> 00:15:45.639 transmitting and receiving was similar to those employed on the 254 00:15:45.679 --> 00:15:49.399 Bristol Channel, that is to say, aerial wires ending above 255 00:15:49.480 --> 00:15:53.159 in metallic sheets. The coil was less powerful than that 256 00:15:53.279 --> 00:15:56.879 used in the former case, giving sparks ten inches in 257 00:15:57.000 --> 00:16:01.360 length only. The apparatus was located during the entire series 258 00:16:01.399 --> 00:16:05.320 of experiments in the electrical laboratory of Saint Bartholomew and 259 00:16:05.399 --> 00:16:08.679 bore an aerial line about seventy five feet in height, 260 00:16:09.039 --> 00:16:12.720 which was afterward prolonged to ninety terminating in a square 261 00:16:12.759 --> 00:16:16.039 metal sheet of about eight feet in the side. On 262 00:16:16.120 --> 00:16:19.720 the first three days, the eleventh, twelfth, and thirteenth of July, 263 00:16:20.159 --> 00:16:23.240 the experiments were executed on land, which gave very good 264 00:16:23.240 --> 00:16:25.360 results up to a distance of three and a half 265 00:16:25.480 --> 00:16:29.639 kilometers or say two miles. On the fourteenth of July, 266 00:16:29.720 --> 00:16:32.200 the receiver was set up on board a tug having 267 00:16:32.200 --> 00:16:35.039 a mast about fifty feet in height, which bore an 268 00:16:35.080 --> 00:16:37.840 aerial wire of equal length ending in a sheet about 269 00:16:37.879 --> 00:16:42.240 eight feet in the side. The transmitting station was bound 270 00:16:42.279 --> 00:16:46.120 to carry out the following instructions ten minutes after the 271 00:16:46.159 --> 00:16:48.639 start of the tug. It was to send for fifteen 272 00:16:48.720 --> 00:16:52.799 minutes dots and dashes at intervals of ten seconds, then 273 00:16:52.879 --> 00:16:56.679 transmit a phrase, maintaining between each signal and interval of 274 00:16:56.759 --> 00:17:00.440 ten seconds. Then to suspend transmission four in an interval 275 00:17:00.480 --> 00:17:03.159 of five minutes, after which it should go through the 276 00:17:03.200 --> 00:17:06.440 same round, but with intervals of five seconds instead of 277 00:17:06.480 --> 00:17:10.559 ten between each signal. The tug having started from the 278 00:17:10.599 --> 00:17:14.000 little port of Saint Bartholomew, the receiver registered some signs 279 00:17:14.039 --> 00:17:17.440 even before transmission had begun on land, a fact due 280 00:17:17.480 --> 00:17:21.680 doubtless to extraneous causes. She directed her course toward the 281 00:17:21.680 --> 00:17:25.200 western mouth of the Mole and continued to receive signals, 282 00:17:25.319 --> 00:17:27.839 not however, in the order and in the intervals that 283 00:17:27.920 --> 00:17:31.720 had been pre arranged, but much more frequently. The sky 284 00:17:31.880 --> 00:17:34.720 was covered with stormy clouds, and in the distance lightning 285 00:17:34.799 --> 00:17:38.160 was frequent. Hence it was surmised that beside the signals 286 00:17:38.160 --> 00:17:42.079 that were really transmitted, others, due to atmospheric influence, were 287 00:17:42.119 --> 00:17:45.480 impressing themselves, which rendered the strip of paper on which 288 00:17:45.519 --> 00:17:50.839 they were registered illegible. On again repeating these experiments, after 289 00:17:50.880 --> 00:17:54.599 the storm clouds had disappeared, correspondence came out very clearly, 290 00:17:54.720 --> 00:17:57.960 up to a distance of five thousand, five hundred meters 291 00:17:58.000 --> 00:18:02.039 nearly three miles with a tug stationary. The tug was 292 00:18:02.079 --> 00:18:05.039 again put in motion so as to interpose between itself 293 00:18:05.039 --> 00:18:08.759 and the station of Saint Bartholomew, the point called La Castagne, 294 00:18:09.400 --> 00:18:12.319 in order to ascertain what effect such a screen would 295 00:18:12.359 --> 00:18:16.480 have on signaling. The signals ceased as soon as the 296 00:18:16.519 --> 00:18:19.960 obstacle intervened to recommence on the tug being moved from 297 00:18:19.960 --> 00:18:23.680 its influence. On the return journey, the messages continued to 298 00:18:23.680 --> 00:18:27.519 come out clear and exact. On the seventeenth of July, 299 00:18:27.640 --> 00:18:30.519 trials were made from the same stations of Saint Bartholomew 300 00:18:30.599 --> 00:18:33.920 to the armored ship San Martino, anchored at a distance 301 00:18:33.960 --> 00:18:37.039 of about one on three quarter miles from the transmitting station, 302 00:18:37.799 --> 00:18:40.240 the aerial conductor of which had been carried to a 303 00:18:40.279 --> 00:18:43.319 height of about forty yards, while the ship bore at 304 00:18:43.359 --> 00:18:46.839 the receiver an aerial line first of twenty and then 305 00:18:46.880 --> 00:18:52.119 of thirty yards in height. Transmission succeeded perfectly independent of 306 00:18:52.160 --> 00:18:55.119 the position of the coherer and the receiver, that is 307 00:18:55.160 --> 00:18:57.200 to say, even if they were screened at the sending 308 00:18:57.240 --> 00:19:01.079 station and surrounded by metallic masses under cover or placed 309 00:19:01.079 --> 00:19:12.119 below the waterline in the ship. End of Section thirty one.