-S7A' WILLIAM SIEMENS, F.R.S. 419 



to make each successive number represent an equal increment, or 

 an equal progressive proportion of the sectional area. 



In ordering wire according to the new Board of Trade wiro 

 gaiii^o, the engineer would have to make a lengthy calculation in 

 tin- first place, in order to express its diameter, its weight per unit 

 Im-tli, or its conductivity in rational measure ; hut the greater 

 drawback will arise in the practical use of each wire, to determine 

 either its strength per square inch or per square centimetre, its 

 electric conductivity, or the space it will occupy in a coil. 

 Elaborate calculations will continually have to be resorted to, too 

 complex to impress the mind with those direct perceptions of 

 fitness and proportion which shorten the work of an experienced 

 practitioner. It may be said, however, that the new gauge was 

 not designed for engineers and scientists, who are quite capable to 

 find their way out of any difficulty which may be imposed upon 

 them, but for practical wire-drawers, manufacturers of bird cages, 

 or other humble users who do not care for accuracy, but require 

 some nomenclature, which, although representing different sizes 

 from those in the old Birmingham wire-gauge, they, in their 

 rough and ready practice, will hardly be able to find out the 

 difference. 



As regards the wire-drawers, it can easily be proved that they 

 have long been in the habit of drawing their wire according to 

 specifications in which the diameter is expressed either in deci- 

 mals of the inch or centimetre ; and being myself connected with 

 a firm of telegraph engineers, who have been large users of wire, I 

 may state it as a fact, that for at least the last nine or ten years 

 the contracts given out by them have always been stated according 

 to diameter ascertained, not by a wire gauge, but by means of the 

 infinitely more correct and more convenient micrometer screw, of 

 which a specimen stands before me. It may perhaps be worthy 

 of notice that the pressure of the wire, when pinched in between 

 the two steel faces is limited by means of a spring-ratchet, which 

 yields when resistance is encountered, and thus prevents inaccuracy 

 through flattening of the wire to be measured. 



As regards the bird-cage maker, and other rough users of wire, 

 I should say that the sooner they were taught to use their wire 

 according to measurement, instead of having only the vague 

 notion of the size given by the existing Birmingham Wire Gauge, 



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