Metal microphones are in some respects more interesting theoretically than those of carbon. For example, one has been constructed of two different metals, zinc and iron, which when heated by the flame of a spirit-lamp generates its own current by thermo-electric action. Iron is one of the most useful metals for forming microphones; and one of iron-wire gauze has been found to act with singular clearness when inclosed in a high vacuum, such as that given by an incandescent electric lamp.
SILAS MONK.
A TALE OF LONDON OLD CITY.
IN FOUR CHAPTERS.—CHAPTER II.
That day in the city seemed to Walter as if it would never end. This mystery about Silas Monk was now a matter to him of real interest. Hitherto, the eccentricities of the old man had given him little or no concern; for it had been so long the custom among the clerks to crack their jokes about ‘Silas,’ that nothing which he might do, however queer, could appear otherwise than perfectly consistent with his character. For so many years had Silas Monk been a clerk in the House, that his columns of pounds, shillings, and pence could be traced in the oldest ledgers, it was said, even when books more than a hundred years old were examined. There was no record extant which satisfactorily settled the date of his engagement as a clerk by Armytage and Company. The oldest partners and the oldest clerks, with this one exception of Silas, were dead and buried many years ago.
It was a very old-looking place, this ancient counting-house; it seemed older even than the firm of Armytage, which had seen two centuries. There were railings in front, broken in places, but still presenting some iron spikes among them, standing up with an air of protection before the windows, like sentinels on guard. The stone steps leading up to the entrance were worn by the tread of busy men who had in their time hurried in and out in their race for wealth, and who were now doubtless lying in some old city churchyard hard by.
Walter Tiltcroft having at last finished his ‘rounds,’ as he called his various errands, came back to the old counting-house. The clerks’ office was on the ground-floor. It was a dark and dusty room, with men of various ages seated at long desks, all deeply engaged, with pens in hand and heads bent low, over the business of the firm. No one looked up when Walter entered; every one went on working, as though each individual clerk was a wheel in the great machine which had been going for nearly two hundred years.
Within an inner room, smaller, darker, and more dusty, was seated alone at his desk Silas Monk. The old clerk had several large ledgers before him; he was turning over the leaves with energy, and making entries in these books with a rapidity which seemed surprising in one who had an appearance of such great age. With his white hair falling on his shoulders, his long lean trembling fingers playing among the fluttering pages, and his keen eyes darting among the columns of pounds, shillings, and pence, he seemed, even by daylight, like an embodied spirit appointed by the dead partners and clerks of Armytage and Company to audit the accounts of that old mercantile House in Crutched Friars. So at least thought Walter Tiltcroft as he sat at his own desk watching Silas Monk, and revolving in his mind how he could best solve the mystery which surrounded Rachel’s grandfather.
It was growing dusk when the old city clocks in the church towers began to strike six, and the clerks in the office of Armytage and Company began to show signs of dispersing. Silas Monk alone remained at his post. Wishing to say a few words to the old man before taking his leave, Walter Tiltcroft lingered behind; and when the last clerk had gone, he went to the door of the ‘strong-room,’ as Silas Monk’s office was called, and said in his usual cheerful tone: ‘Good-night, Mr Monk. You’ll see, I suppose, that everything is safe and sound, as usual? Won’t you?’