"Exactly; but how would you do that?"

"Oh, it's easy enough, I believe," said Tom. "You get a sheet of tinfoil, lay it on a table, cover it with quicksilver, and then put the gla.s.s on it, and press it with weights till the tinfoil and quicksilver stick to the gla.s.s, and then you have a regular mirror."

"You seem to know all about it, Tom," said the Vicar, who had dropped in for a chat, and to hear how the telescope was going on.

"I read it somewhere," said Tom.

"And he can always recollect this sort of thing," said his uncle; "but never could remember anything to do with the law."

Tom looked at him reproachfully.

"Well," continued Uncle Richard, "your process would do for ordinary looking-gla.s.ses, Tom, but not for an optical reflector."

"Why, uncle?"

"Because the rays of light would have to pa.s.s through the thickness of the gla.s.s before they reached the reflecting surface,--the quicksilver,--and in so doing they would be refracted--broken-up and discoloured--so that the reflection would most likely be doubled when it came away; that is, you would see one reflection from the silver at the back, and another from the surface of the gla.s.s."

"Therefore," said the Vicar, "we must decline friend Tom's ingenious proposal, and take yours, Brandon, for as usual you have a plan ready."

"Well, yes," said Uncle Richard, smiling; "but it is due to the inventor. We must silver the gla.s.s, but on the surface, so as to get a reflection at once. Are you going to stay, Maxted?"

"If I may," was the reply.

"Very well; but for experiment, as it is all new to me, I think we will try first to silver one of these pieces of the broken speculum. Yes; that largest piece."

The conversation took place in the workshop, and the triangular piece of gla.s.s having been brought out, it was first thoroughly washed, and rinsed with rain-water, and then further cleaned by rubbing it well with a strong acid, so as to burn off any impurity, and after another rinsing in clear rain-water it was declared by Uncle Richard to be chemically clean.

"A good thing to be chemically as well as morally clean, Tom," said the Vicar, smiling; "but I'm not going to stand here without asking questions if you don't, Master Tom. First then, why must the gla.s.s be chemically clean?"

"So that the silver may adhere to it," said Uncle Richard, who was now carefully arranging the freshly-cleaned gla.s.s, so that it lay on two pieces of wood in a shallow tray half full of water.

"My turn to question," said Tom merrily.

"Yes, go on," said the Vicar.

"Why is the face of the gla.s.s put in water, uncle?"

"To keep it wet and thoroughly clean. Dust or floating spores might settle upon it, and then we should have specks. I want to get a surface perfectly clear; and now, Tom, I want the four bottles I prepared yesterday--fetch them down."

Tom ran up into the laboratory, and brought down four great stoppered bottles, each of which bore a label duly lettered.

These he placed on the broad, table-like bench, and on being requested hurried up-stairs again to fetch a large gla.s.s jar-shaped vessel, and a graduated measuring-gla.s.s.

"Now," said Uncle Richard, "this process is a chemical experiment, but upon reading it I felt that it was as good as a conjuring trick, and a very grand one too. In fact it is good enough for a magician, for it is a wonderful example of the way in which our chemists have mastered some of the secrets of Nature."

"Bravo, lecturer!" said the Vicar. "Come, Tom, my boy, give him some applause. Clap your hands and stamp your feet;" and the visitor led off by thumping his umbrella upon the floor.

"Oh, very well," said Uncle Richard, laughing; "it shall be a lecture on silver if you like--a very brief one, with a remarkable experiment to follow."

"More applause, Tom," said the Vicar; and it was given laughingly.

"I have here," continued Uncle Richard, "immersed in distilled water--"

"Rain-water, uncle."

"Well, boy, rain-water is distilled by Nature, and then condensed from the vapoury clouds to fall back upon the earth."

"Good," said the Vicar. "I am learning."

"Next," said Uncle Richard, "I have here a bottle marked A, containing so many grains of pure potash, dissolved in so many ounces of water--a strong alkaline solution in fact."

More applause.

"In this next bottle," continued Uncle Richard, "marked B, I have a strong solution of ammonia."

"Another alkali?" said the Vicar.

"Exactly," said Uncle Richard. "In this bottle, marked C, a solution of sugar-candy prepared with pure spirit. Can I have the pleasure of offering you a gla.s.s, Vicar?"

"Oh no, thanks," was the reply. "I will not spoil the experiment by satisfying my desire for good things."

"Will any other member of the audience?" said Uncle Richard merrily, looking round at Tom.

"I won't, uncle, thankye," said the lad. "You might have labelled the bottles wrongly."

"Wise boy," said the Vicar; "but, by the way, where's the lump of beaten-out silver to be affixed to the gla.s.s?"

"Here it is," said Uncle Richard, laying his hand upon the stopper of the fourth bottle, which held the same quant.i.ty of liquid as the others.

"But that's clear water," said Tom.

"Yes, clear distilled water, but not alone. It contains a great deal of silver."

"Whereabouts, lecturer?" said the Vicar.

"In solution," said Uncle Richard gravely. "Here we have one of the wonders of science laboriously worked out by experiment, and when discovered simplicity itself. Tom, suppose I take a piece of bright clear iron and leave it out exposed to all weathers, what happens?"

"Gets rusty," said Tom.

"Exactly; and what is rust?"

"Red," said Tom.

"So is your face, Tom, for giving so absurd an answer."

"Yes, uncle," said Tom frankly. "I don't quite know."

"Oxide of iron," said the Vicar.