8 5 8 



NA TURE 



[December 23, 1922 



we knew that steel subjected to a certain heat treat- 

 ment had its mechanical qualities altered. Micro- 

 scopic investigation, aided by improvements in the 

 preparation and treatment of the samples to be 

 examined, has enabled us now to trace out, step 

 bv step, the changes which take place at various 

 ■ I the treatment, as well as the effect — in the 

 alloys — of modifications in the proportions 

 of the constituents. Microscopic research also 

 promises to be of value in providing definite informa- 

 tion as to the changes of structure in different metals 

 when injured bv fatigue, or are just on the point of 

 fracture, and Sir Robert Hadfield has made some 

 valuable experiments in this direction. 



During the last few vears a most important 

 addition has been made to our methods of discovering 

 defects in materials or workmanship by the applica- 

 tion of the X-rays. Great progress has been made, 

 and there is every promise of further developments 

 111 the early future. At present steel or iron can be 

 searched to depths of about 3 inches, aluminium 

 and its alloys to about 6 inches, and timbers of 

 various kinds from about 15 to 20 inches. 



Researches on the thermal efficiency of the steam 

 engine during the last few years have related chiefly 

 to the development of the steam turbine. Prior 

 to 1903 the best economical result obtained with 

 a steam turbine was that of a 1500-kilowatt alternator 

 built bv Messrs. Parson in 1902 ; this machine had 

 a steam consumption corresponding to about 13-5 lb. 

 per indicated horse-power per hour. A test carried 

 out in 1918 on a 10,000-kilowatt unit by the same 

 makers gave a consumption of 775 lb. per horse- 

 power per hour — a reduction of about 43 per cent, 

 on the 1902 performance. The corresponding thermal 

 efficiency is nearly 277 per cent. Bearing in mind 

 certain points in the design of this turbine and 

 making allowance for them, it appears that a thermal 

 efficiency of 30 per cent, for a steam motor is within 

 our reach. 



Mechanical gearing in turbines has proved in a 

 number of cases to be unsatisfactory. The question 

 of how to prevent the defects which have occurred 

 forms probably the most important problem which 

 has demanded the attention of mechanical engineers 

 for many years past. The failures have been variously- 



attributed to the use of unsuitable metal for the 

 gears, to irregularity in the gear cutting, to disturb- 

 ance in the alignment of the shafts and to other causes. 

 The whole subject deserves more systematic and 

 thorough investigation than it has received hitherto. 



The development of the steam turbine has been 

 the result of an enormous amount of strenuous and 

 original work, both theoretical and constructional. 

 On the theoretical side, the determination of the laws 

 controlling the discharge of steam through orifices 

 of various shapes is yet very far from being complete, 

 and there are many other problems, such as the 

 critical speeds of shafts, the best number of stages 

 to be adopted under different conditions, and so on. 

 On the constructional side may be mentioned the 

 selection of suitable materials for the blades and the 

 mode of fixing the latter, devices for preventing 

 steam leakage, securing efficient lubrication, and 

 methods of governing and of obtaining the high 

 vacua so essential for securing economic performance. 



The pistons of reciprocating engines have speeds 

 ranging from 600 to 800 feet per minute. In steam 

 turbines the blades are being run successfully at 

 600 feet per second. A small turbine (150 horse- 

 power), made recently by Messrs. Ljungstrom of 

 Stockholm, runs at 40,000 revolutions per minute 

 and has a blade speed of 952 feet per second — more 

 than 1 1 miles per minute. 



In conclusion, Dr. Maw directed attention to one 

 fa< t v, hich appeared to him of far greater importance 

 than all the others : in none of the researches referred 

 to, varied and extensive as they have been, is there 

 the slightest trace of finality. Much as has been 

 discovered and great as has been the progress made, 

 it is most certain that we have at present effected 

 only the preliminary opening up of the mine of 

 knowledge and that the real wealth of its contents 

 is as vet unknown to us. We can only say that the 

 " impossible " of yesterday has become the " possible " 

 of to-day, and in the early future many of these 

 possibilities bid fair to become accomplished facts. 

 Surelv this is a great inheritance, which should 

 invite our coming generations of engineers to make 

 most strenuous efforts to secure greater — and still 

 greater — developments, so that they may in their 

 turn leave behind them a heritage more glorious still. 



Radio-Telephony and Broadcasting. 1 



By A. P. M. Fleming, C.B.E. 



IX 1 Mnsidering the development of radio-telephony, 

 it is frequently overlooked that the earliest 

 methods of communication, such as by sound and 

 light, do not involve the use of wires ; the negative 

 and non-descriptive term " wireless " has, therefore, 

 been displaced by the term " radio." Radio waves 

 are electro-magnetic 111 character, being pulsations in 

 the asther of space, and they differ among themselves 

 and from radiant heat, light, and X-rays, only in 

 their amplitude and wave-length. Some waves change 

 and diminish gradually in amplitude, and are said to 

 be " damped " ; others maintain their amplitude and 

 are " continuous." Radio waves exist and are used 

 which vary in wave-length from a few yards to ten or 

 twelve miles ; they are the longest electro-magnetic 

 waves. 



Given the means whereby electrical waves can be 

 produced and detected, it is comparatively simple to 

 arrange to send signals by the morse code, and this 

 is done every day in ordinary radio-telegraphy. 



1 Substance of a lecture delivered at a meeting of the North-east Coast 

 Institution of Engineers and Shipbuilders, Newcastle-on-Tyne, oh Friday, 

 December 15. 



NO. 2773, VOL. 1 IO] 



Radio-telephonv is in some respects analogous to 

 ordinary telephony. The ordinary telephone circuit 

 of microphone transmitter, line, and receiver contains 

 a battery which sends a continuous current round 

 the circuit and through the telephone receiver. If 

 speech is made in the microphone, the vibration of 

 the microphone diaphragm varies the pressure on 

 carbon grains in the microphone. This varies the 

 resistance in the battery circuit, and the current, 

 instead of flowing steadily, rises and falls according 

 to the sound waves impinging on the transmitter 

 diaphragm. The fluctuating current varies the pull 

 on the diaphragm in the telephone receiver, and this 

 sets up sound waves similar in character to those 

 originally spoken into the transmitter. In radio- 

 telephony there is a generator capable of producing 

 very high-frequency oscillating current which can be 

 radiated from an aerial, just as heat and light are 

 radiated from a fire or lamp. This radiated oscilla- 

 tion is known as a " carrier wave." Near the gen- 

 erator is a modulator receiving the speech and modify- 

 ing the amplitude of the high-frequency oscillation, 

 and imparting changes in the carrier waves in 



