WEBVTT

1
00:00:01.080 --> 00:00:06.519
<v Speaker 1>Section twenty six The Science History of the Universe, Volume three.

2
00:00:07.120 --> 00:00:10.160
<v Speaker 1>This is a LibriVox recording. All LibriVox recordings are in

3
00:00:10.199 --> 00:00:13.679
<v Speaker 1>the public domain. For more information or to volunteer, please

4
00:00:13.759 --> 00:00:18.239
<v Speaker 1>visit LibriVox dot org. The Science History of the Universe,

5
00:00:18.760 --> 00:00:25.160
<v Speaker 1>Volume three, edited by Francis Rolt Wheeler. Electricity, Chapter eight,

6
00:00:25.719 --> 00:00:29.800
<v Speaker 1>the telephone, Part one. In eighteen fifty four, a Frenchman,

7
00:00:30.199 --> 00:00:34.479
<v Speaker 1>Charles Bursull predicted the transmission of speech and outlined a

8
00:00:34.600 --> 00:00:39.159
<v Speaker 1>method correct save in one particular, but for which error

9
00:00:39.439 --> 00:00:43.399
<v Speaker 1>one following his directions could have produced a speaking telephone.

10
00:00:44.000 --> 00:00:47.799
<v Speaker 1>His words at this date seem almost prophetic. I have

11
00:00:47.880 --> 00:00:51.439
<v Speaker 1>asked myself, for example, if the spoken word itself could

12
00:00:51.520 --> 00:00:55.399
<v Speaker 1>not be transmitted by electricity. In a word, if what

13
00:00:55.600 --> 00:00:58.759
<v Speaker 1>was spoken in Vienna may not be heard in Paris,

14
00:00:58.799 --> 00:01:02.799
<v Speaker 1>the thing is practical in this way. Suppose that a

15
00:01:02.880 --> 00:01:07.319
<v Speaker 1>man speaks near a movable disc sufficiently flexible to lose

16
00:01:07.480 --> 00:01:11.239
<v Speaker 1>none of the vibrations of the voice. That this disc

17
00:01:11.359 --> 00:01:14.879
<v Speaker 1>alternately makes and breaks the connection from a battery. You

18
00:01:14.959 --> 00:01:18.400
<v Speaker 1>may have at a distance another disc which will simultaneously

19
00:01:18.439 --> 00:01:23.159
<v Speaker 1>execute the same vibrations the words makes and breaks. In

20
00:01:23.319 --> 00:01:28.079
<v Speaker 1>Borsoul's quotation, have been italicized by the present writer. They

21
00:01:28.159 --> 00:01:31.920
<v Speaker 1>formed the keynote of the failures of those who subsequently

22
00:01:31.959 --> 00:01:38.959
<v Speaker 1>followed Borsoul's directions literally. Philip Reese, a German inventor, constructed

23
00:01:39.000 --> 00:01:42.799
<v Speaker 1>what he called a telephone in eighteen sixty one, following

24
00:01:42.840 --> 00:01:47.560
<v Speaker 1>implicitly the path outlined by Bursul. He mounted a flexible

25
00:01:47.599 --> 00:01:51.280
<v Speaker 1>diaphragm over an opening in a wooden box, and on

26
00:01:51.359 --> 00:01:54.799
<v Speaker 1>the center of the diaphragm fastened a small piece of platinum.

27
00:01:55.200 --> 00:01:58.560
<v Speaker 1>Near this he mounted a heavy brass spring with which

28
00:01:58.599 --> 00:02:03.159
<v Speaker 1>the platinum alternately made and broke contact when the diaphragm

29
00:02:03.400 --> 00:02:07.640
<v Speaker 1>was caused to vibrate. These contact points formed the terminals

30
00:02:07.640 --> 00:02:10.960
<v Speaker 1>of a circuit containing a battery and the receiving instrument.

31
00:02:11.639 --> 00:02:16.159
<v Speaker 1>His receiver assumed various forms, prominent among which was a

32
00:02:16.240 --> 00:02:20.439
<v Speaker 1>knitting needle wrapped with silk insulated copper wire and mounted

33
00:02:20.479 --> 00:02:24.120
<v Speaker 1>on a cigar box for a sounding board. Its operation

34
00:02:24.560 --> 00:02:27.199
<v Speaker 1>was as follows. The sound waves set up in the

35
00:02:27.240 --> 00:02:30.680
<v Speaker 1>air struck against the diaphragm of the transmitter, causing it

36
00:02:30.719 --> 00:02:34.080
<v Speaker 1>to vibrate in unison with them. This caused the alternate

37
00:02:34.159 --> 00:02:36.400
<v Speaker 1>making and breaking of the circuit at the point of

38
00:02:36.479 --> 00:02:40.479
<v Speaker 1>contact between the platinum and the spring, and allowed intermittent

39
00:02:40.560 --> 00:02:44.240
<v Speaker 1>currents to flow through the receiver. These caused a series

40
00:02:44.280 --> 00:02:47.520
<v Speaker 1>of sounds in the kneading needle. By virtue of Page's effect,

41
00:02:48.360 --> 00:02:51.840
<v Speaker 1>the sounding board vibrated in unison with the molecular vibrations

42
00:02:51.879 --> 00:02:55.080
<v Speaker 1>of the needle, and the sound was thus greatly amplified.

43
00:02:55.800 --> 00:02:59.879
<v Speaker 1>Reese's telephone could be depended upon to transmit only musical sounds.

44
00:03:00.400 --> 00:03:03.479
<v Speaker 1>The question as to whether it actually did transmit speech

45
00:03:03.520 --> 00:03:06.759
<v Speaker 1>has been the subject of much discussion. But if it

46
00:03:06.800 --> 00:03:10.840
<v Speaker 1>did this at all, it was very imperfectly. The cause

47
00:03:10.919 --> 00:03:14.000
<v Speaker 1>of its failure, says K. B. Miller in his American

48
00:03:14.080 --> 00:03:19.479
<v Speaker 1>Telephone Practice. To successfully transmit speech will be understood from

49
00:03:19.479 --> 00:03:23.439
<v Speaker 1>the following facts. A simple musical tone is caused by

50
00:03:23.520 --> 00:03:27.639
<v Speaker 1>vibrations of very simple forms, while sound waves produced by

51
00:03:27.680 --> 00:03:30.800
<v Speaker 1>the voice in speaking are very complex and their nature.

52
00:03:31.639 --> 00:03:36.840
<v Speaker 1>Sound possesses three qualities, pitch depending entirely on the frequency

53
00:03:36.840 --> 00:03:41.360
<v Speaker 1>of the vibrations, loudness depending on the amplitude of the vibrations,

54
00:03:41.400 --> 00:03:45.919
<v Speaker 1>and tambre or quality depending on the form of the vibration.

55
00:03:46.919 --> 00:03:49.639
<v Speaker 1>The tones of a flute and a violin may be

56
00:03:49.759 --> 00:03:53.960
<v Speaker 1>the same as to pitch and loudness, yet be radically different.

57
00:03:55.039 --> 00:04:00.840
<v Speaker 1>This difference is in tambre or quality. Reese's transmitter, as

58
00:04:00.840 --> 00:04:03.479
<v Speaker 1>he adjusted, it was able only to make and break

59
00:04:03.560 --> 00:04:06.719
<v Speaker 1>the circuit, and a movement of the diaphragm barely sufficient

60
00:04:06.759 --> 00:04:09.759
<v Speaker 1>to break the circuit produced the same effect as a

61
00:04:09.840 --> 00:04:13.479
<v Speaker 1>much greater movement. The current therefore flowed with full strength

62
00:04:13.520 --> 00:04:17.040
<v Speaker 1>until the circuit was broken. When it stopped entirely, the

63
00:04:17.120 --> 00:04:21.639
<v Speaker 1>intermediate strengths needed for reproducing the delicate modulations of the

64
00:04:21.720 --> 00:04:26.879
<v Speaker 1>voice were entirely lacking. This apparatus could therefore exactly reproduce

65
00:04:27.000 --> 00:04:29.639
<v Speaker 1>the pitch of a sound, but not its timbre and

66
00:04:29.800 --> 00:04:34.680
<v Speaker 1>relative loudness. For the next fifteen years, no apparent advance

67
00:04:34.800 --> 00:04:37.759
<v Speaker 1>was made in the art of telephony, although several inventors

68
00:04:37.839 --> 00:04:42.439
<v Speaker 1>gave it their attention. In eighteen seventy six, Professor Alexander

69
00:04:42.480 --> 00:04:48.279
<v Speaker 1>Graham Bell and Professor Elisha Gray almost simultaneously invented successful

70
00:04:48.360 --> 00:04:52.240
<v Speaker 1>speaking telephones. Gray has been one of the principal claimants

71
00:04:52.279 --> 00:04:55.360
<v Speaker 1>for the honor of being the first inventor of the telephone,

72
00:04:55.680 --> 00:04:58.839
<v Speaker 1>but Bell has apparently established his right to it, and

73
00:04:58.920 --> 00:05:03.360
<v Speaker 1>has also reaped the prophet for after long litigation. The

74
00:05:03.480 --> 00:05:06.920
<v Speaker 1>United States Patent Office and the courts have awarded the

75
00:05:06.959 --> 00:05:11.399
<v Speaker 1>priority to him, as against Gray and many others. Bell

76
00:05:11.560 --> 00:05:15.480
<v Speaker 1>possessed a greater knowledge of acoustics than of electrical science,

77
00:05:15.839 --> 00:05:18.720
<v Speaker 1>and it was probably this that led him to appreciate

78
00:05:19.199 --> 00:05:23.639
<v Speaker 1>wherein others had failed. His instrument consisted of a permanent

79
00:05:23.759 --> 00:05:27.920
<v Speaker 1>bar magnet, having on one end a coil of fine wire.

80
00:05:28.639 --> 00:05:31.480
<v Speaker 1>In front of the pole carrying the coil, a thin

81
00:05:31.600 --> 00:05:35.319
<v Speaker 1>diaphragm of soft iron was so mounted as to allow

82
00:05:35.680 --> 00:05:39.839
<v Speaker 1>its free vibration close to the pole. Two points will

83
00:05:39.879 --> 00:05:43.800
<v Speaker 1>be noticed, says Miller in the work before sighted, which

84
00:05:43.839 --> 00:05:47.720
<v Speaker 1>have heretofore been absent, That no battery is used in

85
00:05:47.759 --> 00:05:51.240
<v Speaker 1>the circuit, and that the transmitting and receiving instruments are

86
00:05:51.399 --> 00:05:56.560
<v Speaker 1>exactly alike. When the soft iron diaphragm of the transmitting

87
00:05:56.600 --> 00:06:00.759
<v Speaker 1>instrument is spoken to, it vibrates in exact accordance with

88
00:06:01.000 --> 00:06:04.680
<v Speaker 1>the sound waves striking against it. The movement of the

89
00:06:04.759 --> 00:06:08.839
<v Speaker 1>diaphragm causes changes in the magnetic field in which lies

90
00:06:08.920 --> 00:06:13.040
<v Speaker 1>the coil, which changes has already pointed out, cause currents

91
00:06:13.079 --> 00:06:16.079
<v Speaker 1>to flow in the circuit. These currents flow first in

92
00:06:16.120 --> 00:06:19.680
<v Speaker 1>one direction, and then in the other varying in unison

93
00:06:19.800 --> 00:06:24.040
<v Speaker 1>with movements of the diaphragm, the waves being very complex

94
00:06:24.160 --> 00:06:29.360
<v Speaker 1>as represented graphically passing along the line wire. These electrical

95
00:06:29.439 --> 00:06:33.519
<v Speaker 1>impulses so feeble that only the most delicate instruments can

96
00:06:33.560 --> 00:06:37.560
<v Speaker 1>detect them. Alternately increase and decrease the strength of the

97
00:06:37.560 --> 00:06:41.680
<v Speaker 1>permanent magnet of the receiving instrument, and thereby cause it

98
00:06:41.720 --> 00:06:45.879
<v Speaker 1>to exert a varying pull on its soft iron diaphragm,

99
00:06:46.000 --> 00:06:49.480
<v Speaker 1>which as result takes up the vibrations and reproduces the

100
00:06:49.480 --> 00:06:54.519
<v Speaker 1>sound faithfully. Bell's earlier instruments were exhibited in eighteen seventy

101
00:06:54.560 --> 00:06:58.399
<v Speaker 1>six at the Centennial in Philadelphia. The receiver consisted of

102
00:06:58.439 --> 00:07:02.720
<v Speaker 1>a tubular magnet composed of a coil of wire surrounding

103
00:07:02.839 --> 00:07:06.680
<v Speaker 1>a core and enclosed in an iron tube which was

104
00:07:06.720 --> 00:07:10.279
<v Speaker 1>about quarter inches in diameter and three inches long. This

105
00:07:10.439 --> 00:07:14.079
<v Speaker 1>tube was closed by a thin iron armature or diaphragm,

106
00:07:14.240 --> 00:07:17.399
<v Speaker 1>which rested loosely on the upper face of the iron tube,

107
00:07:17.759 --> 00:07:19.879
<v Speaker 1>the length of the core being such as not quite

108
00:07:19.920 --> 00:07:23.600
<v Speaker 1>to touch the diaphragm when in this position. The whole

109
00:07:23.600 --> 00:07:26.319
<v Speaker 1>of it was mounted on a base, arrangements being made

110
00:07:26.360 --> 00:07:28.519
<v Speaker 1>to adjust the air gap between the pole of the

111
00:07:28.519 --> 00:07:32.560
<v Speaker 1>core and the diaphragm by means of a thumbscrew. The

112
00:07:32.600 --> 00:07:36.120
<v Speaker 1>transmitter consisted of an electro magnet in front of the core,

113
00:07:36.480 --> 00:07:40.759
<v Speaker 1>on which was adjustably mounted, a diaphragm of gold beater's

114
00:07:40.800 --> 00:07:44.600
<v Speaker 1>skin carrying a small iron armature at its center. A

115
00:07:44.720 --> 00:07:48.560
<v Speaker 1>long mouthpiece into which the sounds to be transmitted were spoken,

116
00:07:49.000 --> 00:07:52.439
<v Speaker 1>served to convey the sound waves more directly to the diaphragm.

117
00:07:53.120 --> 00:07:56.759
<v Speaker 1>Nearly all books and articles on telephones, says Miller, that

118
00:07:56.879 --> 00:07:59.959
<v Speaker 1>treat of Bell's earlier receiver at all show and describe

119
00:08:00.199 --> 00:08:03.720
<v Speaker 1>it as having the diaphragm fastened at one edge by

120
00:08:03.759 --> 00:08:06.720
<v Speaker 1>a single small screw to the upper face of the

121
00:08:06.759 --> 00:08:09.920
<v Speaker 1>iron tube, and sprung away from the tube at its

122
00:08:09.920 --> 00:08:14.000
<v Speaker 1>opposite side. This mistake occurred in the first two editions

123
00:08:14.040 --> 00:08:16.199
<v Speaker 1>of this work, and would have been in this one

124
00:08:16.399 --> 00:08:18.959
<v Speaker 1>but for Thomas D. Lockwood, who was kind enough to

125
00:08:19.040 --> 00:08:21.959
<v Speaker 1>call attention to it. The origin of the error is

126
00:08:22.040 --> 00:08:25.480
<v Speaker 1>explained in the following interesting extract from a letter written

127
00:08:25.480 --> 00:08:29.040
<v Speaker 1>by mister Lockwood to the writer of this book. This

128
00:08:29.160 --> 00:08:32.759
<v Speaker 1>mistake first appeared in the account given by Engineering of

129
00:08:32.960 --> 00:08:38.159
<v Speaker 1>Sir William Thompson's address to the British Association in September

130
00:08:38.399 --> 00:08:43.360
<v Speaker 1>eighteen seventy six, and has been universally copied. The origin

131
00:08:43.399 --> 00:08:47.320
<v Speaker 1>of the mistake is very odd. The screw of the instrument,

132
00:08:47.720 --> 00:08:51.519
<v Speaker 1>given to Sir William Thompson, and which he exhibited in

133
00:08:51.600 --> 00:08:54.759
<v Speaker 1>England on his return, was put through a hole in

134
00:08:54.840 --> 00:08:58.519
<v Speaker 1>the edge of the diaphragm and engaged with the threaded

135
00:08:58.559 --> 00:09:01.399
<v Speaker 1>whole of the tube for the purpose of attaching the

136
00:09:01.440 --> 00:09:05.600
<v Speaker 1>diaphragm while in transit to prevent it from getting lost.

137
00:09:06.960 --> 00:09:10.840
<v Speaker 1>No one, however, notified Sir William of this, it probably

138
00:09:10.919 --> 00:09:14.480
<v Speaker 1>having been forgotten, and Sir William seems to have forgotten

139
00:09:14.519 --> 00:09:18.919
<v Speaker 1>what the instrument as he saw in Philadelphia looked like. Finally,

140
00:09:18.960 --> 00:09:22.320
<v Speaker 1>in knocking about among Sir William's luggage, the free end

141
00:09:22.399 --> 00:09:27.960
<v Speaker 1>of the diaphragm was apparently, and without doubt unintentionally bent upward,

142
00:09:28.320 --> 00:09:31.919
<v Speaker 1>as the picture shows. But when so bent, being at

143
00:09:31.960 --> 00:09:35.679
<v Speaker 1>the same time rigidly fastened at the opposite edge, it

144
00:09:35.720 --> 00:09:39.320
<v Speaker 1>would not and could not work, And when Sir William

145
00:09:39.399 --> 00:09:43.759
<v Speaker 1>showed it in England, he couldn't make it work. Bell's instrument,

146
00:09:43.919 --> 00:09:47.679
<v Speaker 1>in a modified form, is the standard of today. It

147
00:09:47.759 --> 00:09:52.080
<v Speaker 1>is now used as a receiver, only a more efficient transmitter,

148
00:09:52.200 --> 00:09:57.559
<v Speaker 1>depending upon entirely different principles having been invented. In speaking

149
00:09:57.639 --> 00:10:03.960
<v Speaker 1>of Bell's invention, Sir William Thompson, Lord Kelvin, said, who

150
00:10:04.000 --> 00:10:08.279
<v Speaker 1>can but admire the hardihood of invention which devised such

151
00:10:08.440 --> 00:10:12.720
<v Speaker 1>very slight means to realize the mathematical conception that, if

152
00:10:12.759 --> 00:10:17.399
<v Speaker 1>electricity is to convey all the delicacies of quality which

153
00:10:17.519 --> 00:10:22.039
<v Speaker 1>distinguish articulate speech, the strength of its current must vary

154
00:10:22.080 --> 00:10:26.480
<v Speaker 1>continuously as nearly as may be in simple proportion to

155
00:10:26.559 --> 00:10:30.960
<v Speaker 1>the velocity of a particle of air engaged in constituting

156
00:10:30.960 --> 00:10:34.440
<v Speaker 1>the sound. Much has been said and books have been

157
00:10:34.480 --> 00:10:37.039
<v Speaker 1>written on the rights of Reee as the inventor of

158
00:10:37.080 --> 00:10:41.240
<v Speaker 1>the speaking telephone. The validity of Bell's controlling patent was

159
00:10:41.279 --> 00:10:45.120
<v Speaker 1>the subject of many attacks, the litigation finally reaching the

160
00:10:45.159 --> 00:10:48.399
<v Speaker 1>Supreme Court of the United States. In the opinion of

161
00:10:48.440 --> 00:10:52.440
<v Speaker 1>this Court October Term eighteen eighty seven, the following brief

162
00:10:52.480 --> 00:10:56.639
<v Speaker 1>but comprehensive statement is found. We have not had our

163
00:10:56.799 --> 00:11:00.320
<v Speaker 1>attention called to a single item of evidence which hens

164
00:11:00.360 --> 00:11:02.960
<v Speaker 1>in any way to show that Reese or anyone who

165
00:11:03.000 --> 00:11:06.519
<v Speaker 1>wrote about him, had in his mind that anything else

166
00:11:06.600 --> 00:11:10.000
<v Speaker 1>than the intermittent current caused by the opening and closing

167
00:11:10.080 --> 00:11:13.159
<v Speaker 1>of the circuit could be used to do what was wanted.

168
00:11:14.360 --> 00:11:16.399
<v Speaker 1>No one seems to have thought that there could be

169
00:11:16.480 --> 00:11:20.879
<v Speaker 1>another way. All recognized the fact that the minor differences

170
00:11:20.919 --> 00:11:26.039
<v Speaker 1>in the original vibrations had not been satisfactorily reproduced, but

171
00:11:26.080 --> 00:11:30.559
<v Speaker 1>they attributed it to the imperfect mechanism of the apparatus used,

172
00:11:31.159 --> 00:11:33.960
<v Speaker 1>rather than to any fault in the principle on which

173
00:11:34.000 --> 00:11:37.639
<v Speaker 1>the operation was to depend. It was left for Bell

174
00:11:37.799 --> 00:11:40.720
<v Speaker 1>to discover that the failure was due not to workmanship,

175
00:11:41.000 --> 00:11:44.200
<v Speaker 1>but to the principle which was adopted as the basis

176
00:11:44.279 --> 00:11:47.360
<v Speaker 1>of what had to be done. He found that what

177
00:11:47.399 --> 00:11:51.480
<v Speaker 1>he called the intermittent current, one caused by alternatively opening

178
00:11:51.559 --> 00:11:54.679
<v Speaker 1>and closing the circuit, could not be made under any

179
00:11:54.720 --> 00:11:59.000
<v Speaker 1>circumstances to reproduce the delicate forms of the air vibrations

180
00:11:59.039 --> 00:12:02.360
<v Speaker 1>caused by the human voice in articulate speech, but that

181
00:12:02.399 --> 00:12:05.679
<v Speaker 1>the true way was to operate on an unbroken current

182
00:12:05.759 --> 00:12:10.399
<v Speaker 1>by increasing and diminishing its intensity. Such was his discovery,

183
00:12:10.799 --> 00:12:14.480
<v Speaker 1>and it was new. Reese never thought of it, and

184
00:12:14.559 --> 00:12:18.519
<v Speaker 1>he failed to transmit speech telegraphically. Bell did, and he

185
00:12:18.600 --> 00:12:23.639
<v Speaker 1>succeeded Under such circumstances, it is impossible to hold that

186
00:12:23.679 --> 00:12:27.639
<v Speaker 1>what Reese did was an anticipation of the discovery of Bell.

187
00:12:28.200 --> 00:12:30.840
<v Speaker 1>To follow Reese is to fail, but to follow Bell

188
00:12:31.039 --> 00:12:34.519
<v Speaker 1>is to succeed. The difference between the two is just

189
00:12:34.559 --> 00:12:39.840
<v Speaker 1>the difference between failure and success. A very interesting fact,

190
00:12:40.159 --> 00:12:43.159
<v Speaker 1>and one which might have changed the entire commercial status

191
00:12:43.159 --> 00:12:46.360
<v Speaker 1>of the telephone industry, is that in eighteen sixty eight,

192
00:12:46.759 --> 00:12:50.879
<v Speaker 1>Royal e House of Binghamton, New York, invented and patented

193
00:12:51.120 --> 00:12:55.679
<v Speaker 1>an electrophonetic telegraph which was capable of operating as a

194
00:12:55.720 --> 00:13:00.360
<v Speaker 1>magneto telephone in the same manner as the instrument's subsequently

195
00:13:00.559 --> 00:13:04.480
<v Speaker 1>devised by Bell. House knew nothing of its capabilities, however,

196
00:13:04.879 --> 00:13:08.960
<v Speaker 1>unfortunately for him, the instrument is provided with a sounding

197
00:13:09.039 --> 00:13:13.759
<v Speaker 1>diaphragm of pine wood, stiffened with varnish, mounted in one

198
00:13:13.919 --> 00:13:17.759
<v Speaker 1>end of a large sound amplifying chamber, so formed as

199
00:13:17.799 --> 00:13:20.600
<v Speaker 1>to focus the sound waves at a point near its

200
00:13:20.639 --> 00:13:24.360
<v Speaker 1>mouth where the ear was to be placed to receive them.

201
00:13:24.639 --> 00:13:28.519
<v Speaker 1>The electromagnet, adapted to be connected in the line circuit,

202
00:13:28.840 --> 00:13:31.639
<v Speaker 1>had its armature connected by a rod with the center

203
00:13:31.720 --> 00:13:35.399
<v Speaker 1>of the wooden diaphragm. By this means any movements imparted

204
00:13:35.399 --> 00:13:38.679
<v Speaker 1>to the armature by fluctuating currents in the line were

205
00:13:38.720 --> 00:13:43.159
<v Speaker 1>transmitted to the diaphragm, causing it to give out corresponding sounds,

206
00:13:43.639 --> 00:13:46.840
<v Speaker 1>and any movements imparted to the diaphragm by sound waves

207
00:13:46.840 --> 00:13:50.480
<v Speaker 1>were transmitted to the armature, causing its movements to induce

208
00:13:50.559 --> 00:13:55.480
<v Speaker 1>corresponding currents and the line. Two of these instruments, connected

209
00:13:55.480 --> 00:13:59.159
<v Speaker 1>in a circuit would act alternately as transmitters and receivers

210
00:13:59.559 --> 00:14:03.320
<v Speaker 1>in the same manner as Bell's instruments. It has been

211
00:14:03.360 --> 00:14:06.679
<v Speaker 1>shown that in order to transmit speech by electricity, it

212
00:14:06.759 --> 00:14:11.240
<v Speaker 1>is necessary to cause an undulatory or alternating current to

213
00:14:11.360 --> 00:14:13.919
<v Speaker 1>flow in the circuit over which the transmission is to

214
00:14:13.960 --> 00:14:17.039
<v Speaker 1>be effected, and that the strength of this current at

215
00:14:17.080 --> 00:14:21.559
<v Speaker 1>all times be in exact accordance with the vibratory movements

216
00:14:21.559 --> 00:14:25.600
<v Speaker 1>of the body producing the sound. Bell's magnetic transmitter was

217
00:14:25.720 --> 00:14:29.200
<v Speaker 1>used as the generator of this current, as a dynamo.

218
00:14:29.360 --> 00:14:32.879
<v Speaker 1>In fact, the energy for driving which was derived from

219
00:14:32.919 --> 00:14:36.159
<v Speaker 1>the sound waves set up by the voice. The amount

220
00:14:36.159 --> 00:14:40.480
<v Speaker 1>of energy so derived was however, necessarily very small and

221
00:14:40.519 --> 00:14:45.240
<v Speaker 1>the current correspondingly weak, and for this reason was not

222
00:14:45.320 --> 00:14:49.919
<v Speaker 1>a practical form of transmitter except for comparatively short lines.

223
00:14:51.279 --> 00:14:55.000
<v Speaker 1>Elisha Gray devised a transmitter which, instead of generating the

224
00:14:55.120 --> 00:15:00.639
<v Speaker 1>undulatory current itself, depended for its action on causing variation

225
00:15:00.720 --> 00:15:04.320
<v Speaker 1>in the strength of a current generated by some separate source.

226
00:15:05.120 --> 00:15:08.639
<v Speaker 1>This variation and current strength always being in accordance with

227
00:15:08.679 --> 00:15:12.960
<v Speaker 1>the movement of the diaphragm. He mounted on his horizontal

228
00:15:13.080 --> 00:15:17.960
<v Speaker 1>vibrating diaphragm a metal needle extending into a fluid of

229
00:15:18.039 --> 00:15:22.600
<v Speaker 1>low conductivity, such as water. The needle formed one terminal

230
00:15:22.639 --> 00:15:25.679
<v Speaker 1>of the circuit, the other terminal being a metal pin

231
00:15:25.919 --> 00:15:29.240
<v Speaker 1>extending up through the bottom of the containing vessel. The

232
00:15:29.320 --> 00:15:32.559
<v Speaker 1>vibrations of the diaphragm was supposed to cause changes in

233
00:15:32.600 --> 00:15:36.759
<v Speaker 1>the resistance of the path through the fluid on account

234
00:15:36.840 --> 00:15:40.039
<v Speaker 1>of the varying distance between the points of the electrodes,

235
00:15:40.320 --> 00:15:43.440
<v Speaker 1>and therefore corresponding changes in the strength of the current.

236
00:15:44.360 --> 00:15:48.120
<v Speaker 1>Bell also used a liquid transmitter, in which a conducting

237
00:15:48.240 --> 00:15:52.200
<v Speaker 1>liquid was held in a conducting vessel, forming one terminal

238
00:15:52.240 --> 00:15:55.639
<v Speaker 1>of the circuit. The other terminal was a short metallic

239
00:15:55.720 --> 00:16:00.639
<v Speaker 1>needle carried on the diaphragm and projecting slightly into the liquid,

240
00:16:00.799 --> 00:16:03.840
<v Speaker 1>so that the area of contact between the liquid and

241
00:16:03.879 --> 00:16:07.039
<v Speaker 1>the needle would be varied to better advantage by the

242
00:16:07.159 --> 00:16:10.240
<v Speaker 1>vibration of the diaphragm than if the needle were immersed

243
00:16:10.320 --> 00:16:15.000
<v Speaker 1>a greater distance into the fluid. Bell's liquid transmitter depended

244
00:16:15.080 --> 00:16:18.559
<v Speaker 1>on variation in the extent of immersion of the electrode,

245
00:16:18.759 --> 00:16:22.039
<v Speaker 1>while Gray's instrument, owing to the great extent to which

246
00:16:22.080 --> 00:16:25.519
<v Speaker 1>the pin was immersed, depended rather on the variation and

247
00:16:25.559 --> 00:16:29.080
<v Speaker 1>the length of the conducting path through the liquid itself,

248
00:16:29.679 --> 00:16:33.960
<v Speaker 1>a faulty principle for this purpose. Bell's liquid transmitter was

249
00:16:34.000 --> 00:16:38.759
<v Speaker 1>also exhibited at the Philadelphia Centennial in eighteen seventy six, and,

250
00:16:39.039 --> 00:16:43.399
<v Speaker 1>unlike that of Reese, simply caused variations in the resistance

251
00:16:43.399 --> 00:16:47.360
<v Speaker 1>of the circuit, and thereby allowed a continuous but undulatory

252
00:16:47.480 --> 00:16:51.120
<v Speaker 1>current to pass over the line, the variations in which

253
00:16:51.159 --> 00:16:54.200
<v Speaker 1>were able to reproduce all the delicate shades of timber,

254
00:16:54.679 --> 00:16:59.799
<v Speaker 1>loudness and pitch necessary inarticulate speech. Gray and Bell in

255
00:16:59.799 --> 00:17:03.879
<v Speaker 1>bodied or attempted to embody in these instruments. The main

256
00:17:03.960 --> 00:17:08.799
<v Speaker 1>principle upon which all successful battery transmitters are based. A

257
00:17:08.880 --> 00:17:13.000
<v Speaker 1>battery furnished the current and the transmitter actuated by the

258
00:17:13.119 --> 00:17:17.440
<v Speaker 1>voice served to modulate it. It was not long, however,

259
00:17:17.519 --> 00:17:20.599
<v Speaker 1>before a much better means was devised for putting this

260
00:17:20.720 --> 00:17:24.960
<v Speaker 1>principle into practice. End of Section twenty six