874 nEPOKT — 1887. 



MOXJDAY, SEPTEMBER 5. 



The following Papers were read : — 



1. On Copper Wire. By W. H. Preece, F.U.S. 



Four copper wii-es have recently been erected between London and Dublin. 

 The aerial portion was built with No. I2|, -097 incli in diameter, weighing 150 

 pounds per mile, liaving a specified resistance of 605" per mile and a tensile 

 strength of 490 pounds, or 29^ tons per inch. 



The resistance per mile when erected was 5-69o" at 30° F. The capacity per 

 mile was -01319 microfarad, and the insulation per mile was 70 megohms at 30° F. 



Copper wire is subject to strict inspection. It is gauged and tested for ductility 

 and for tensile strength. The wire now supplied exceeds the specified demand. 

 Its tensile strength equals 30-6 tons per square inch, and its conductivity is 98 per 

 cent, of that of pure copper. An entirely new method of wiring has been adopted. 

 The wire is drawn up and regulated to its proper stress by a dynamometer. The 

 factor of safety is 4. A table is given showing the sags and stresses with varying 

 .spans and temperatui-es for iron and copper. The wii-e is bound to the insulator 

 by finer copper wire, and the joints are the form known as the ' Britannia ' and 

 soldered. It requires very careful handling to avoid indentation. Scratches and 

 kinks are very injurious. It is practically free from the throttling effect of electro- 

 magnetic mertia, and by the reduction in resistance and capacity it has trebled the 

 •efficiency of aerial wires. Various copper wires are now being erected. 



2. Fast Speed Telegraphii.^ By W. H. Preece, F.E.S. 



The author explained that the object of his paper was to describe the evolution 

 of the system of fast speed telegraphy since it left the hands of AVheatstone and 

 Stroh. The foUo'W'ing table illustrates the progress made : — 



Year 



These results have been the consequences of: (1) Greater perfection of appara- 

 tus ; (2) the elimination of electromagnetic inertia ; (3) the improvement of cir- 

 cuits ; (4) introduction of high-speed repeaters. 



A complete set of automatic instruments consists of: (1) the perforator, which 

 punches a strip of paper with holes on the principle of the Jacquard loom, so as to 

 regulate the number, order, and rate at which alternate currents of electricity are 

 sent along a wire by (2) the transmitter, which is the automatic part of the appara- 

 tus, sending along the line those currents which at the distant end are recorded as 

 words in the form of dots and dashes, replacing the slow and uncertain manipula- 

 tion of the hand ; (3) the receiver, which is an ink writer of extreme delicacy and 

 great rapidity, recording the words in the Morse character. 



As the speed of transmission increased, it was found that one great source of 

 trouble was the sparking at the points of contact, which dirties them by disintegrating 

 the metal. Small condensers of J^ microfarad capacity have been applied, and the 

 evil thereby considerably modified ; but it has been still further reduced bj switch- 

 ing out the galvanometer while the transmitter is at worlv, for sparking is princi- 

 pally due to the presence of electromagnetic inertia in the apparatus. 



' Published in extenso in Industries, vol. iii. p. 296. 



