. The science-history of the universe . 4inches in diameter and 3 inches long. This tube wasclosed by a thin iron armature, or diaphragm, which rested 264 ELECTRICITY loosely on the upper face of the iron tube, the length ofthe core being such as not quite to touch the diaphragmwhen in this position. The whole was mounted on a base,arrangements being made to .adjust the air gap betweenthe pole of the core and the diaphragm by means of athumbscrew. The transmitter consisted of an electromagnet in frontof the core, on which was adjustably mounted a diaphragmof goldbeaters skin carrying a small i
. The science-history of the universe . 4inches in diameter and 3 inches long. This tube wasclosed by a thin iron armature, or diaphragm, which rested 264 ELECTRICITY loosely on the upper face of the iron tube, the length ofthe core being such as not quite to touch the diaphragmwhen in this position. The whole was mounted on a base,arrangements being made to .adjust the air gap betweenthe pole of the core and the diaphragm by means of athumbscrew. The transmitter consisted of an electromagnet in frontof the core, on which was adjustably mounted a diaphragmof goldbeaters skin carrying a small iron armature atits center. A long mouthpiece, into which the sounds to. Fig- 35 —Bells Centennial Transmitter. (From MillersAmerican Telephone Practice.) be transmitted were spoken, served to convey the soundwaves more directly to the diaphragm. Nearly all books and articles on telephones, saysMiller, that treat of Bells early receiver at all, show anddescribe it as having the diaphragm fastened at one edgeby a single small screw to the upper face of the iron tube,and sprung away from the tube at its opposite side. Thismistake occurred in the first two editions of this work, andwould have been in this one but for Thomas D. Lock-wood, who was kind enough to call attention to it. Theorigin of the error is explained in the following inter-esting extract from a letter written by Mr. Loekwood tothe writer of this book: THE TELEPHONE 265 This mistake first appeared in the account given byEngineering of Sir William Thomsons address to theBritish Association in September, 1876, and has been uni-versally copied. The origin of the mistake is very screw of
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