TKASSACXIONS OF SECTION G. 79"3 



wax, ploughing out, by means of a -vibratory stylus, a narrow undulating groove, 

 which constituted a sound record. When this groove was retraced by another 

 stylus and diaphragm, the original sounds were reproduced with a fidelity un- 

 dreamed of by those only acquainted with the phonograph. In 1885 the Volta 

 Laboratory Association was dissolved, after performing most important work, and 

 taking out a series of valuable patents. 



Mr. Tainter has brought the experience of years to the perfection of the 

 graphophone. The kernel of the invention is the ' recording cylinder,' six inches 

 long by an inch-and-a-quarter broad, formed of cardboard, coated with wax. This 

 is placed in a small lathe and rotated by a treadle in contact with the ' recorder,' 

 which consists of a metal frame supporting a thin mica diaphragm, in the centre 

 of which is a steel point that cuts a narrow groove on the surface of the cylinder, 

 according to the quality and intensity of the sound spoken against it. The re- 

 corder is then removed, and replaced by the ' reproducer,' a light feather of steel 

 that travels along the grooves made on the cylinder, and transmits theii- undula- 

 tions to a small mica diaphragm, which in its turn communicates its vibrations, as 

 sound-waves, to the ears of the auditor by means of two india-rubber tubes, for 

 Mr. Tainter found it best to reduce the size of the record, and concentrate the 

 sound in this way, on account of the greater distinctness that was thus secured. 

 The manipulation of the graphophone is simplicity itself. It requires no adjust- 

 ment, no electric motor, no galvanic battery. The foot supplies the motive power, 

 and the machine regulates its own speed by means of an ingenious, but simple 

 governor. Journalists and reporters may dictate their articles and reports, leaving 

 others to transcribe them. The principal of a firm can speak his day's correspond- 

 ence into the machine, which will repeat it sentence by sentence, to be written 

 down in proper form by pen or typewriter. Or purely verbal communication can 

 be carried on through the post by means of the record cylinders, which are ex- 

 tremely light, although capacious enough to hold one thousand words a piece. All 

 these applications are now in active operation in America, where the graphophone 

 Las achieved a great success. 



3. Mechanical Pathology considered in its relation to Bridge Design} 

 By G. H. Thomson, M.Am.S.E. 



After pointing out the applicability of the ordinary terms of medical science in 

 the consideration of mechanical problems the author asks, How many railway 

 bridges are structurally competent to perform the work for which they were 

 erected ? How many are being taxed mechanically beyond the limit ever in- 

 tended ? And how many are able to withstand the sometimes rough usage (as in 

 the case of collisions) incidental to railroad operations ? 



A railway bridge is ordinarily constructed upon the assumption that all the 

 conditions governing its use and life will always remain favourable, and the non- 

 recognition of the fact that an unfavourable combination of circumstances may 

 occur is responsible for many of the deficiencies that occur in practice. 



No less than 251 truss railway bridges have failed in the United States and 

 Canada during the ten years ending December 1887 from preventable causes such 

 as are here alluded to, involving in each case the wreck wholly or partially of a 

 train. 



The author investigates the causes of these several accidents under different 

 headings. He discusses successively broken axles and wheels, increase of tonnage, 

 power, and speed. 



He doubts the utility of laboratory tests as a means of affording thoroughly 

 reliable information in regard to broken axles, and points out that whereas the 

 earliest engine used in America only weighed 0-875 ton per wheel, those now in 

 use weigh eight tons and upwards. Since 1874 the speed of freight trains on the 

 New York Central has increased from fifteen to twenty-five miles per hour, and 

 passenger trains at times attain a maximum speed of no less than 74 miles an hour. 



' Printed in extenso in I^ngimering, vol. xlvi. p. 252. 



