November 21, 1912] 



NATURE 



545 



clibtrict of Egypt, and the primitive tools and methods 

 employed at the mines were described. 



Egypt was also noted for having produced the first 

 mining map in the world, a map showing a gold 

 mining region of the time of Seti I. or Rameses II. 

 (1350 to 1330 B.C.). 



The influence of silver and lead on the development 

 of primitive culture was shown to be insignificant, 

 the latter metal only becoming of importance during 

 the supremacy of the Romans, in connection with 

 their elaborate systems for the supply and distribution 

 of water and in the construction of baths. 



.\s regards iron, the belief that the first iron gener- 

 ally known to man was either of meteoric origin or 

 telluric native iron was not supported by any sub- 

 stantial evidence. Nor was such origin necessary, as 

 iron ores are so easily reducible that they can be 

 converted into metallic iron in an ordinary charcoal 

 fire. They are, in fact, reduced to metal at a con- 

 siderably lower temperature than the ores of copper. 



The earliest iron smelting in Europe was traced to 

 the upper waters of the Danubian tributaries, the 

 ancient Noricum, but in still earlier times iron was 

 extracted from its ores in the region on the south-east 

 of the Euxine, in Ferghana and other localities in 

 .^sia. In Africa, so far as metallurgical evidence may 

 bs depended on, the extraction of iron from its ores was 

 carried on at a remote date. That this early African 

 iron smelting w-as known in Egypt is well shown by 

 a bas-relief on a stone now in the Egyptian collection 

 in Florence. 



THE BORDERLAND BETWEEN ELEC- 

 TRICITY AND OTHER SCIENCES.'' 

 'T'HERE are applications of electricity that give 

 ^ work to many men, applications wjfiich employ 

 much plant and apparatus, and on which large sums 

 of money are spent, about which we have heard very 

 little or nothing in the institution. Again, we hear 

 little, if anything, about what is occurring on what I 

 may term the borderland between electricity and the 

 other sciences. In this borderland or fringe a large 

 number of scientific workers are quietly at work, and 

 what is to-day a laboratory experiment may to-morrow 

 form the basis of a large industry. Finally, we should 

 have an opportunity of discussing the many details 

 in the design and operation of electrical plant and 

 ap])aratus, the importance of which cannot be over- 

 estimated. 



Wireless Telegraphy and Telephony. — Correspond- 

 ing to each spark at the transmitter of a wireless 

 telegraphy plant, a train of oscillations is received, 

 and these trains of oscillations are rectified by the 

 detector, and in general are passed through a tele- 

 phone as an indicator. At each spark a click is heard 

 in the telephone, so that with 600 sparks a second the 

 diaphragm is attracted 600 times, producing a some- 

 what musical note. 



Herein lies one of the great advantages of high- 

 spark frequency. 



There seems no doubt that the combination of 

 the human ear and a telephone is much more 

 sensitive for high-frequency notes than for low. 

 In some tests I have made, using an alternating 

 current to determine the minimum power re- 

 quired to produce an audible signal in a telephone 

 receiver at different frequencies, I found in one case 

 that the power was reduced from 430 micro-micro- 

 watts at 300 frequency to 7*7 micro-microwatts at qoo 

 frequency. At higher frequencies it increased again. 



1 From the prciidential address delivered to the Institution of Electrical 

 Engineers on November 14 by Mr. W. Dnddell, F.R.S. 



NO. 2247, VOL. go] 



Due to atmospheric causes, there is generally audible 

 in the telephone receiver clicks and noises commonly 

 spoken of as atmospherics or strays. With high- 

 spark frequencies the human ear easily distinguishes 

 the musical note from these atmospherics ; this enables 

 the operators to read through a large amount of 

 extraneous interference. The elimination or com- 

 pensation of these atmospherics is one of the most 

 important outstanding problems in wireless telegraphy. 



When operating with continuous waves practically 

 no note is heard in the receiver telephone unless the 

 currents are chopped up into rapidly recurring groups 

 of waves either at tlie transmitter (tone sender) or at 

 the receiving end (ticker). 



In order to make a permanent record of the signals, 

 and to allow of high-speed working, the rectified cur- 

 rent from the detector may be passed through a 

 galvanometer or a relay, and here we come to one of 

 the difficult problems which requires solution, namely 

 the construction of a relay or recording instrument 

 xr hich will make a record of the very small received 

 currents at high speeds. The Einthoven or string 

 galvanometer, which is at present used for this pur- 

 pose, is delicate and gives a photographic record. 



Although the difficulties may be minimised, I do 

 not feel at this moment that the photographic method 

 of recording, with the attendant chemicals, and the 

 necessity of handling moist slip, can be looked upon as 

 the final solution from the point of view of commer- 

 cial telegraphy. 



The problem of constructing a relay for this purpose 

 is a very difficult one. The mean current strength 

 of the signals, after rectification by a high-resistance 

 detector, is of the order of ,V to j;Vi of a microampere, 

 and the amount of power availalale to work the in- 

 strument is only of the order of a few micro-micro- 

 watts. For high-speed reception the number of con- 

 tacts to be made and broken per second may be any- 

 thing up to fifty. The problem before our instrument- 

 makers is to construct a relay or recorder which will 

 operate with a power not exceeding a few micro- 

 microwatts at the rate of fifty signals pier second. 



Of the sister science, namely wireless telephony, 

 there is not so much to relate. A certain amount of 

 progress has been made, but the details of the methods 

 used have not been made public. The principle is 

 simple. Given continuous oscillations or a spark 

 frequency above the limits of audibility, you may vary 

 the antenna current, and hence the radiation by 

 means of a microphone, in the same way as a con- 

 tinuous current is varied by the microphone in 

 ordinary telephony. As the radiation varies accord- 

 ing to the modulation of the current by the voice the 

 received current will be varied in the same manner 

 and the voice will be reproduced. The difficulties are 

 mainly in the transmitter. First, we require a per- 

 fectly steady source of continuous oscillations, and 

 secondly a microphone capable of modulating the large 

 powers required to transmit any distance. Over short 

 distances of a few miles there are no difficulties. _ It 

 is only when we come to distances of fifty to 100 miles 

 that the engineering problems become troublesome. 

 In view of the progress that is being made in the 

 high-frequency alternator, and of how much more easy 

 it is to modify the power given out by an alternator, 

 it will not be surprising if, as soon as high-frequency 

 alternators are in use, wireless telephony over com- 

 paratively long distance becomes a working possibility. 



Electrochemistry and Electrometallurgy. — The 

 amount of power installed for chemical and metall- 

 urgical purposes is very large indeed. Exact data are 

 wanting, but it seems probable that the power em- 

 ployed in these processes in Norway and at Niagara 

 may already reach i,ooo,ono kw. One of the neces- 



