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|Publisher:||Random House Publishing Group|
About the Author
Date of Birth:December 16, 1917
Date of Death:March 19, 2008
Place of Birth:Minehead, Somerset, England
Place of Death:Sri Lanka
Education:1948, King's College, London, first-class honors in Physics and Mathematics
Read an Excerpt
"Don't you mean 'rarefications'?"
"I do not. I doubt if such a word exists, and if it does, it shouldn't," retorted Purvis, with the aplomb of Sir Alan Herbert dropping a particularly revolting neologism into his killing-bottle. "Where was I? Explaining sound, of course. When we make any sort of noise, from the faintest whisper to that concussion that went past just now, a series of pressure changes moves through the air. Have you ever watched shunting engines at work on a siding? You see a perfect example of the same kind of thing. There's a long line of goods-wagons, all coupled together. One end gets a bang, the first two trucks move together--and then you can see the compression wave moving right along the line. Behind it the reverse thing happens--the rarefaction--I repeat, rarefaction--as the trucks separate again.
"Things are simple enough when there is only one source of sound--only one set of waves. But suppose you have two wave-patterns, moving in the same direction? That's when interference arises, and there are lots of pretty experiments in elementary physics to demonstrate it. All we need worry about here is the fact--which I think you will all agree is perfectly obvious--that if one could get two sets of waves exactly out of step, the total result would be precisely zero. The compression pulse of one sound wave would be on top of the rarefaction of another--net result--no change and hence no sound. To go back to my analogy of the line of wagons, it's as if you gave the last truck a jerk and a push simultaneously. Nothing at all would happen.
"Doubtless some of you will already see what I am driving at, andwill appreciate the basic principle of the Fenton Silencer. Young Fenton, I imagine, argued in this manner. 'This world of ours,' he said to himself, 'is too full of noise. There would be a fortune for anyone who could invent a really perfect silencer. Now, what would that imply ...?'
"It didn't take him long to work out the answer: I told you he was a bright lad. There was really very little in his pilot model. It consisted of a microphone, a special amplifier, and a pair of loudspeakers. Any sound that happened to be about was picked up by the mike, amplified and inverted so that it was exactly out of phase with the original noise. Then it was pumped out of the speakers, the original wave and the new one cancelled out, and the net result was silence.
"Of course, there was rather more to it than that. There had to be an arrangement to make sure that the cancelling wave was just the right intensity--otherwise you might be worse off than when you started. But these are technical details that I won't bore you with. As many of you will recognise, it's a simple application of negative feed-back."
"Just a moment!" interrupted Eric Maine. Eric, I should mention, is an electronics expert and edits some television paper or other. He's also written a radio play about space-flight, but that's another story. "Just a moment! There's something wrong here. You couldn't get silence that way. It would be impossible to arrange the phase ..."
Purvis jammed the pipe back in his mouth. For a moment there was an ominous bubbling and I thought of the first act of "Macbeth." Then he fixed Eric with a glare.
"Are you suggesting," he said frigidly, "that this story is untrue?"
"Ah--well, I won't go as far as that, but ..." Eric's voice trailed away as if he had been silenced himself. He pulled an old envelope out of his pocket, together with an assortment of resistors and condensers that seemed to have got entangled in his handkerchief, and began to do some figuring. That was the last we heard from him for some time.
"As I was saying," continued Purvis calmly, "that's the way Fenton's Silencer worked. His first model wasn't very powerful, and it couldn't deal with very high or very low notes. The result was rather odd. When it was switched on, and someone tried to talk, you'd hear the two ends of the spectrum--a faint bat's squeak, and a kind of low rumble. But he soon got over that by using a more linear circuit (dammit, I can't help using some technicalities!) and in the later model he was able to produce complete silence over quite a large area. Not merely an ordinary room, but a full-sized hall. Yes....
"Now Fenton was not one of these secretive inventors who won't tell anyone what they are trying to do, in case their ideas are stolen. He was all too willing to talk. He discussed his ideas with the staff and with the students, whenever he could get anyone to listen. It so happened that one of the first people to whom he demonstrated his improved Silencer was a young Arts student called--I think--Kendall, who was taking Physics as a subsidiary subject. Kendall was much impressed by the Silencer, as well he might be. But he was not thinking, as you may have imagined, about its commercial possibilities, or the boon it would bring to the outraged ears of suffering humanity. Oh dear no! He had quite other ideas.
"Please permit me a slight digression. At College we have a flourishing Musical Society, which in recent years has grown in numbers to such an extent that it can now tackle the less monumental symphonies. In the year of which I speak, it was embarking on a very ambitious enterprise. It was going to produce a new opera, a work by a talented young composer whose name it would not be fair to mention, since it is now well-known to you all. Let us call him Edward England. I've forgotten the title of the work, but it was one of these stark dramas of tragic love which, for some reason I've never been able to understand, are supposed to be less ridiculous with a musical accompaniment than without. No doubt a good deal depends on the music.
"I can still remember reading the synopsis while waiting for the curtain to go up, and to this day have never been able to decide whether the libretto was meant seriously or not. Let's see--the period was the late Victorian era, and the main characters were Sarah Stampe, the passionate postmistress, Walter Partridge, the saturnine gamekeeper, and the squire's son, whose name I forget. It's the old story of the eternal triangle, complicated by the villager's resentment of change--in this case, the new telegraph system, which the local crones predict will Do Things to the cows' milk and cause trouble at lambing time.
"Ignoring the frills, it's the usual drama of operatic jealousy. The squire's son doesn't want to marry into the Post Office, and the gamekeeper, maddened by his rejection, plots revenge. The tragedy rises to its dreadful climax when poor Sarah, strangled with parcel tape, is found hidden in a mail-bag in the Dead Letter Department. The villagers hang Partridge from the nearest telegraph pole, much to the annoyance of the linesmen. He was supposed to sing an aria while he was being hung: that is one thing I regret missing. The squire's son takes to drink, or the Colonies, or both: and that's that.
"I'm sure you're wondering where all this is leading: please bear with me for a moment longer. The fact is that while this synthetic jealousy was being rehearsed, the real thing was going on back-stage. Fenton's friend Kendall had been spurned by the young lady who was to play Sarah Stampe. I don't think he was a particularly vindictive person, but he saw an opportunity for a unique revenge. Let us be frank and admit that college life does breed a certain irresponsibility--and in identical circumstances, how many of us would have rejected the same chance?
"I see the dawning comprehension on your faces. But we, the audience, had no suspicion when the overture started on that memorable day. It was a most distinguished gathering: everyone was there, from the Chancellor downwards. Deans and professors were two a penny: I never did discover how so many people had been bullied into coming. Now that I come to think of it, I can't remember what I was doing there myself.
"The overture died away amid cheers, and, I must admit, occasional cat-calls from the more boisterous members of the audience. Perhaps I do them an injustice: they may have been the more musical ones.
"Then the curtain went up. The scene was the village square at Doddering Sloughleigh, circa 1860. Enter the heroine, reading the postcards in the morning's mail. She comes across a letter addressed to the young squire and promptly bursts into song.
"Sarah's opening aria wasn't quite as bad as the overture, but it was grim enough. Luckily, we were to hear only the first few bars....
"Precisely. We need not worry about such details as how Kendall had talked the ingenuous Fenton into it--if, indeed, the inventor realised the use to which his device was being applied. All I need say is that it was a most convincing demonstration. There was a sudden, deadening blanket of silence, and Sarah Stampe just faded out like a TV programme when the sound is turned off. Everyone was frozen in their seats, while the singer's lips went on moving silently. Then she too realised what had happened. Her mouth opened in what would have been a piercing scream in any other circumstances, and she fled into the wings amid a shower of postcards.
"Thereafter, the chaos was unbelievable. For a few minutes everyone must have thought they had lost the sense of hearing, but soon they were able to tell from the behaviour of their companions that they were not alone in their deprivation. Someone in the Physics Department must have realised the truth fairly promptly, for soon little slips of paper were circulating among the V.I.P.'s in the front row. The Vice-Chancellor was rash enough to try and restore order by sign-language, waving frantically to the audience from the stage. By this time I was too sick with laughter to appreciate such fine details.
"There was nothing for it but to get out of the hall, which we all did as quickly as we could. I think Kendall had fled--he was so overcome by the effect of the gadget that he didn't stop to switch it off. He was afraid of staying around in case he was caught and lynched. As for Fenton--alas, we shall never know his side of the story. We can only reconstruct the subsequent events from the evidence that was left.
"As I picture it, he must have waited until the hall was empty, and then crept in to disconnect his apparatus. We heard the explosion all over the college."
"The explosion?" someone gasped.
"Of course. I shudder to think what a narrow escape we all had. Another dozen decibels, a few more phons--and it might have happened while the theatre was still packed. Regard it, if you like, as an example of the inscrutable workings of providence that only the inventor was caught in the explosion. Perhaps it was as well: at least he perished in the moment of achievement, and before the Dean could get at him."
"Stop moralising, man. What happened?"
"Well, I told you that Fenton was very weak on theory. If he'd gone into the mathematics of the Silencer he'd have found his mistake. The trouble is, you see, that one can't destroy energy. Not even when you cancel out one train of waves by another. All that happens then is that the energy you've neutralized accumulates somewhere else. It's rather like sweeping up all the dirt in a room--at the cost of an unsightly pile under the carpet.
"When you look into the theory of the thing, you'll find that Fenton's gadget wasn't a silencer so much as a collector of sound. All the time it was switched on, it was really absorbing sound energy. And at that concert, it was certainly going flat out. You'll understand what I mean if you've ever looked at one of Edward England's scores. On top of that, of course, there was all the noise the audience was making--or I should say was trying to make--during the resultant panic. The total amount of energy must have been terrific, and the poor Silencer had to keep on sucking it up. Where did it go? Well, I don't know the circuit details--probably into the condensers of the power pack. By the time Fenton started to tinker with it again, it was like a loaded bomb. The sound of his approaching footsteps was the last straw, and the overloaded apparatus could stand no more. It blew up."
For a moment no-one said a word, perhaps as a token of respect for the late Mr. Fenton. Then Eric Maine, who for the last ten minutes had been muttering in the corner over his calculations, pushed his way through the ring of listeners. He held a sheet of paper thrust aggressively in front of him.
"Hey!" he said. "I was right all the time. The thing couldn't work. The phase and amplitude relations...."
Purvis waved him away.
"That's just what I've explained," he said patiently. "You should have been listening. Too bad that Fenton found out the hard way."
He glanced at his watch. For some reason, he now seemed in a hurry to leave.
"My goodness! Time's getting on. One of these days, remind me to tell you about the extraordinary thing we saw through the new proton microscope. That's an even more remarkable story."
He was half way through the door before anyone else could challenge him. Then George Whitley recovered his breath.
"Look here," he said in a perplexed voice. "How is it that we never heard about this business?"
Purvis paused on the threshold, his pipe now burbling briskly as it got into its stride once more. He glanced back over his shoulder.
"There was only one thing to do," he replied. "We didn't want a scandal--de mortuis nil nisi bonum, you know. Besides, in the circumstances, don't you think it was highly appropriate to--ah--hush the whole business up? And a very good night to you all."