'Please don't trouble. I'm quite cured. I'm fine.'
The Doctor began to feel the tension in the room. He looked at the black box on the bench, then he looked at the man. 'You've got your hat on,' he said.
'Oh, have I?' Klausner reached up, removed the hat, and put it on the bench.
The Doctor came up closer and bent down to look into the box. 'What's this?' he said. 'Making a radio?'
'No, just fooling around.'
'It's got rather complicated-looking innards.'
'Yes,' Klausner seemed tense and distracted.
'What is it?' the Doctor asked. 'It's rather a frightening-looking thing, isn't it?'
'It's just an idea.'
'Yes?'
'It has to do with sound, that's all.'
'Good heavens, man! Don't you get enough of that sort of thing all day in your work?'
'I like sound.'
'So it seems.' The Doctor went to the door, turned, and said, 'Well, I won't disturb you. Glad your throat's not worrying you any more.' But he kept standing there looking at the box, intrigued by the remarkable complexity of its inside, curious to know what this strange patient of his was up to. 'What's it really for?' he asked. 'You've made me inquisitive.'
Klausner looked down at the box, then at the Doctor, and he reached up and began gently to scratch the lobe of his right ear. There was a pause. The Doctor stood by the door, waiting, smiling.
'All right, I'll tell you, if you're interested.' There was another pause, and the Doctor could see that Klausner was having trouble about how to begin.
He was shifting from one foot to the other, tugging at the lobe of his ear, looking at his feet, and then at last, slowly, he said, 'Well, it's like this... the theory is very simple really. The human ear... you know that it can't hear everything. There are sounds that are so low-pitched or so high-pitched that it can't hear them.'
'Yes,' the Doctor said. 'Yes.'
'Well, speaking very roughly, any note so high that it has more than fifteen thousand vibrations a second - we can't hear it. Dogs have better ears than us. You know you can buy a whistle whose note is so high-pitched that you can't hear it at all. But a dog can hear it.'
'Yes, I've seen one,' the Doctor said.
'Of course you have. And up the scale, higher than the note of that whistle, there is another note - a vibration if you like, but I prefer to think of it as a note. You can't hear that one either. And above that there is another and another rising right up the scale for ever and ever and ever, an endless succession of notes... an infinity of notes... there is a note - if only our ears could hear it - so high that it vibrates a million times a second... and another a million times as high as that... and on and on, higher and higher, as far as numbers go, which is... infinity... eternity... beyond the stars.'
Klausner was becoming more animated every moment. He was a small frail man, nervous and twitchy, with always moving hands. His large head inclined towards his left shoulder as though his neck were not quite strong enough to support it rigidly. His face was smooth and pale, almost white, and the pale-grey eyes that blinked and peered from behind a pair of steel spectacles were bewildered, unfocused, remote. He was a frail, nervous, twitchy little man, a moth of a man, dreamy and distracted; suddenly fluttering and animated; and now the Doctor, looking at that strange pale face and those pale-grey eyes, felt that somehow there was about this little person a quality of distance, of immense immeasurable distance, as though the mind were far away from where the body was.
The Doctor waited for him to go on. Klausner sighed and clasped his hands tightly together. 'I believe,' he said, speaking more slowly now, 'that there is a whole world of sound about us all the time that we cannot hear. It is possible that up there in those high-pitched inaudible regions there is a new exciting music being made, with subtle harmonies and fierce grinding discords, a music so powerful that it would drive us mad if only our ears were tuned to hear the sound of it. There may be anything... for all we know there may -'
'Yes,' the Doctor said. 'But it's not very probable.'
'Why not? Why not?' Klausner pointed to a fly sitting on a small roll of copper wire on the workbench. 'You see that fly? What sort of a noise is that fly making now? None - that one can hear. But for all we know the creature may be whistling like mad on a very high note, or barking or croaking or singing a song. It's got a mouth, hasn't it? It's got a throat!'
The Doctor looked at the fly and he smiled. He was still standing by the door with his hands on the doorknob. 'Well,' he said. 'So you're going to check up on that?'
'Some time ago,' Klausner said, 'I made a simple instrument that proved to me the existence of many odd inaudible sounds. Often I have sat and watched the needle of my instrument recording the presence of sound vibrations in the air when I myself could hear nothing. And those are the sounds I want to listen to. I want to know where they come from and who or what is making them.'
'And that machine on the table there,' the Doctor said, 'is that going to allow you to hear these noises?'
'It may. Who knows? So far, I've had no luck. But I've made some changes in it and tonight I'm ready for another trial. This machine,' he said, touching it with his hands, 'is designed to pick up sound vibrations that are too high-pitched for reception by the human ear, and to convert them to a scale of audible tones. I tune it in, almost like a radio.'
'How d'you mean?'