Dec. 1st, 1887.] 



SCIENTIFIC NEWS. 



231 



The description given is a general one, as there are many 

 systems in use, mainly differing in the pattern of the ap- 

 paratus employed. One system in use in the United States 

 enables every operator in an exchange, however large, to 

 see whether the line she wants is engaged or not, and to 

 connect the calling-line to it directlj', without communi- 

 cating with any other operator. The connections and 

 amount of apparatus involved in such a system can, how- 

 ever, hardly compensate for the increased simplicity of 

 ■working. A large exchange fitted up in this way must be 

 the most complicated system of electrical connections in 

 existence, and one feels inclined to pity the man responsible 

 for repairs and additions to it. 



The number of subscribers connected to each switchboard 

 should be such as to just engross the attention of the 

 operator. This number varies with the size of the ex- 

 change, other things being equal, as the number of calls 

 per wire increases, in about the same proportion as the 

 number of subscribers on the exchange; or, in other words, 

 and speaking roughly, the total number of calls in a given 

 time is proportional to the square of the number of sub- 

 scribers connected to it. 



As has already been hinted, the telephone has been 

 utilised for a number of scientific researches. The 

 sensitiveness ot the Bell receiver to alternating or 

 intermittent currents has enabled electricians to use it in 

 investigating many phenomena which are otherwise not 

 easily brought under our ken. Professor Hughes has taken 

 the lead in these applications, and has been enabled to de- 

 monstrate several new and interesting facts in magnetic 

 and electrical science. Incidentally, by means of his induc- 

 tion balance, he has given the scientific world a means of 

 discovering exceedingly slight differences in the composi- 

 tion, form, or weight of two pieces of metal — e.g., two coins, 

 which should be identical ; and by another application of 

 the same instrument, which has a Bell telephone for its in- 

 dicator, has shown surgeons how to localise a bullet or other 

 foreign metallic substance in the human body without 

 probing for it. He has also shown why an iron wire is far 

 less efficient as a conductor for a telephone or a rapidly- 

 working telegraph line than a copper wire. The fact had 

 been observed before, but the reasons were not clearly 

 known. The Postal Telegraph Department has not been 

 slow to utilise the fact, and has already erected many hun- 

 dreds of miles of copper wire for rapid telegraphy, with 

 the result that the highest speed that could be obtained be- 

 tween London and Newcastle on an iron wire was increased 

 12^ per cent., or from 368 to 414 words per minute, by 

 the simple substitution of a copper line wire. 



As the copper is lighter than the iron, and need not cost 

 more, this is a very useful practical result. The Telegraph 

 Department found it out experimentally by erecting nearly 

 300 miles of wire. Professor Hughes, with the help of his 

 clever utilisation of the sensitive Bell telephone, showed 

 the same fact as clearly with ten inches of each kind of wire. 



To mention and briefly explain all the scientific uses of 

 the telephone would lead us to nearly every branch 

 of physical science, and swell this article to far beyond any 

 permissible length. 



The commercial uses are being rapidly extended by 

 " trunk lines," connecting the telephone exchanges of neigh- 

 bouring towns. For example, London subscribers can 

 speak to Brighton subscribers, and Glasgow to Edinburgh, 

 whilst most of the manufacturing districts of the north and 

 midland counties have their various towns connected to- 

 gether ; and soon it will be possible for a Liverpool sub- 

 scriber to speak to a subscriber on any exchange in the 

 South Yorkshire district, as well as any in Lancashire, 

 Cheshire, and Derbyshire. 



This subject leads into the question of long-distance tele- 

 phony, which requires separate treatment, and involves a 

 good many rather abstruse technical points. Long-distance 

 telephony is, however, an accomplished fact, and Brussels 

 and Paris are now regularly connected with a telephone wire. 



As great a distance as 1,000 miles is said to have been 

 spoken over in the United States; and, given a suitably 

 built and environed line, there is no reason to doubt the 

 assertion. 



For military telegraphic purposes the telephone promises 

 to be extremely valuable. Used as a speaking instrument, no 

 specially-trained staff is required to work it ; but its use as 

 a "Morse sounder" is likely to be of even more practical 

 value, as its extreme sensitiveness enables it to be used on 

 badly-insulated and connected lines that no ordinary tele- 

 graph instrument can work through. This same sensitiveness 

 enables the battery power to be reduced to a minimum ; batte- 

 ries being heavy and troublesome, this is an important point. 



In Germany and some other states, the telephone is uted 

 by the telegraph departments for the service of the smaller 

 offices, and no skill being required to use it, a considerable 

 saving in operation and maintenance is effected. 



The subject of this series is a very large one, both from 

 the scientific and practical point of view, and it has hardly 

 touched on many important and interesting points. It is 

 necessarily imperfect in many respects, but it is hoped that 

 enough has been said to give an insight into the modus 

 operandi of this most important and useful invention, and to 

 interest some readers in the subject and in the far wider 

 subject of electricity and its applications. 



In conclusion, the acknowledgments of the writer must 

 be given to Professor Silvanus Thomson for information 

 derived from his most interesting book on Reiss' connection 

 with the telephone, and his courtesy and that of Messrs. 

 Spon in allowing some of the blocks of that work to be used 

 for illustrating these articles ; similar acknowledgments are 

 due to other publishers for favours of the same nature 



FOLDED FILTERS. 



BY the usual method of folding a filter paper, a small 

 proportion only of the paper is effective, so chemists 

 and others engaged in work where rapid filtration is neces- 

 sary, have been in the habit of folding their filter paper. 



somewhat in the manner shown in the accompanying illus- 

 tration. Messrs. Schleicher and Schull, of Diiren, in Ger- 

 many, recognising the loss of time thus occasioned, are now 

 selling filter paper folded ready for use in various sizes, 

 and we strongly recommend their use 



