416 SECTION MECHANICS. 



velocity. Now, Sir William Thomson has devised two or three forms 

 of instruments, one of which is simply a needle instrument ; but, 

 instead of having the needle a mass of matter which moves, the needle 

 is a mere spot of light, or rather the indicator is a spot of light, the 

 needle proper being an excessively minute piece of steel so light that, 

 if I remember rightly, it only weighs about a quarter of a grain. 

 From this mirror instrument he has proceeded to what he calls his 

 Recorder, and there he records upon a strip of paper a thin line 

 of ink, not made by the depression of a wheel or a pen, or any 

 apparatus upon the paper, but simply by a small thin film of ink that 

 is spurted upon it by electrical repulsion. There is no instrument 

 more beautiful in construction than this of Sir William Thomson's, 

 and I am very sorry it is not here for you to see. Probably in a week 

 or two one will be fitted up in the collection, and it will be well worth 

 your inspection. 



Now I have rapidly glanced through the different systems of 

 apparatus in use in England and generally throughout the world. In 

 England we really have at the present moment five systems in use, 

 each of which may be called, as I said at first, an example of the 

 survival of the fittest. We have the ABC, which is used at all small 

 post-offices where skilled labour, from its expense, cannot be employed 

 that is, where messages are few and far between ; sometimes where 

 they only reach one a week, others one a day, and so on, where busi- 

 ness is slack. It is also used very largely between the merchant and 

 his office, between the hall and the stable, between the counting-house 

 and the drawing-room, and for various purposes of that kind. As 

 business increases and the offices become more important, so we in- 

 troduce the single-needle instrument, which has this especial merit 

 that it does not require skilled labour. It also has the advantage that 

 a number of instruments can be connected together on the same wire. 

 Sometimes on railways from twelve to fifteen instruments are formed 

 on one circuit. On post-office circuits eight and sometimes ten have 

 been so applied. As the business of the station increases, some 

 proceed from the single-needle to the Morse system, and in the Morse 

 system I include the Sounder. The Morse system is really and truly 

 a relic of the past. Its doom has been sealed so far as England is 

 concerned, and we are replacing the Morse instrument by the more 



