720 



NA TURE 



[June 3, 1922 



other's messages in a confused babel of sounds, but will 

 interfere with other forms of radio-communication, 

 as already happens to a considerable extent in 

 America. 



The most important consideration is that of wave- 

 length, as simultaneous messages at or near the same 

 wave-length mutually " jam " one another, and it 

 may be mentioned that the margin of wave-lengths 

 within which wireless telephone apparatus can be 

 made to " tune out " other messages is not so fine as 

 it is with the best class of wireless telegraph receivers. 

 In order to avoid interference with other estabHshed 

 services, the Post Office has allotted the range of 350 

 to 425 metres to the broadcasting stations. In this 

 connection it should be recalled that the greater part 

 of ship and shore Morse communication is on a 300 to 

 600 metre wave, and that amateur stations are allowed 

 a wave-length of 440 metres. The well-known Writtle 

 station will work in future at 400 metres, and the Air 

 Ministry wave-lengths are 900 metres for the Croydon 

 aeroplane service and 1400 metres for long-range weather 

 reports, etc., while most of the powerful stations use 

 longer waves up to the 2500 metres of the Eiffel Tower. 

 Possibility of interference will also be limited by allow- 

 ing broadcasting only between the hours of 5 and 11 

 P.M. on week-days or any time on Sundays. 



Further considerations are the locality and range 

 of the transmitting stations. To avoid too much 

 overlapping, one station will probably be allowed at 

 each of the following points : London, Cardiff, Ply- 

 mouth, Birmingham, Manchester, Edinburgh, Glasgow, 

 and Aberdeen, and arrangements will be made between 

 the licencees at these stations as to wave-lengths 

 and times of operation within the allotted limits. 



With the view of circumscribing to some extent the 

 field of each station, its power will be limited to that 

 corresponding to an input of ij kw. The actual 

 distance over which a station can be heard, however, 

 depends more on the receiving than on the transmitting 

 apparatus, but with modern delicate equipment an 

 approximate idea of the possible working range is 

 given by taking about \ mile for every watt input. 

 Thus, although a simple set may only be able to 

 hear the nearest of such a group of stations, a really 

 sensitive set, say in London, could readily pick up all 

 of them. 



The cost of a receiving set for private use in picking 

 up whatever programmes are to be broadcasted, varies 

 considerably with its sensitiveness. Roughly, the 



minimum that need be expended will depend on the 

 distance from the nearest public station, assuming 

 that to be the only one the owner desires to hear. A 

 set of this kind with a range of 25 miles or so would 

 cost from 5Z. to loZ. complete with the simple aerial 

 that would be necessary. Actually, however, the 

 cost of the equipment selected for any particular case 

 will depend upon whether the apparatus is required 

 to be used to pick up waves from longer distances as 

 well, such as to hear the wireless concerts already 

 being radiated from the Hague, and the time and other 

 signals from the Eiffel Tower. In this case a detector 

 of the thermionic valve tube type must be em- 

 ployed, with one or more degrees of amplification and 

 a greater range of tuning inductances, etc., and a 

 multicell dry battery or other source of voltage for 

 the tubes, as well as the two-cell accumulator, which 

 would otherwise be sufficient. A moderately sensitive 

 apparatus of this kind, with a range of 75 miles or 

 more, would cost about 20Z., and further requirements 

 of sensitivity could easily bring the price to, say, 

 75Z. Another point influencing the cost of the equip- 

 ment is the class of aerial which it is convenient to 

 use, as the more sensitive the set the smaller is the 

 .aerial with which it will work over a given distance. 

 As a rule, the simple crystal set will require some 

 form of outside aerial, whereas the more delicate set 

 with amplifying valves will give surprising results 

 with a portable aerial, inside a room, composed of a 

 few turns of wire on a rectangular frame. 



Although probably the best results are obtained 

 with these sets by the use of headpiece telephones, 

 loud-speaking sets, audible to a number of persons at 

 once, can be used with all the better-class apparatus, 

 and this feature will doubtless add greatly to the 

 popularity of wireless telephone reception. 



A number of firms are devoting themselves to the 

 ipanufacture of this kind of apparatus, including, of 

 course, such well-known establishments as the Marconi 

 Co. The Radio Communications Corporation is also 

 well to the fore, and, as we have already announced, 

 special arrangements are being made at the Trafford 

 Park Works of the Metropolitan-Vickers Electrical 

 Co. Other firms specialising in wireless receiving ap- 

 paratus suitable for these purposes include Radio 

 Supplies, C. F. Elwell, Ltd., and the R.M. Radio 

 Company. We hope before long to have the oppor- 

 tunity of publishing some particulars of the actual 

 apparatus made by some of these firms. 



Obit 



T. Sandmeyer.i 



HTRAUGOTT SANDMEYER, well known to all 

 J- chemists as the discoverer of the reactions 

 which bear his name, was born at Wettingen in Aargau 

 in 1854. Left an orphan by the death of his father 

 the day after his birth, his mother had to resume her 

 former occupation as a school teacher. His father, 

 who was a science teacher, left a library of scientific 

 books, the perusal of which led young Sandmeyer 

 to interest himself in scientific apparatus, and after 



1 This account is mainly gathered from an interesting obituary notice 

 by Dr. Fierz in the issue of the Journal of the Society of Chemical Industry 

 for May 15. 



NO. 2744, VOL. 109] 



uary. 



spending some time in an engineering workshop, 

 entered the employment of Mr. J. F. Meier, of Zurich, 

 a manufacturer of physical apparatus. Sandmeyer 

 afterwards started business on his own account, and 

 supplied apparatus to the Polytechnic institution. 

 He became in this way connected with the staff of the 

 institution, and in 1882 was appointed lecture-assistant 

 to Victor Meyer. 



The story is often told how Victor Meyer, in attempt- 

 ing to show his class what was then known as the 

 " indophenin reaction " with coal-tar benzene, used 

 benzene obtained by distilling calcium benzoate with 

 lime and failed to produce the expected result. It is 



