Each monk was also expected to go to confession, and that Sunday there was quite a long line at the confessional. Perhaps it was the presence of soldiers, and the threat of war, but every penitent wanted to unburden his soul and cleanse it of any possible remaining sin. It was some time before Brother Gregory got to say "Confiteor".

"The enjoyable admiration of perceived truth, which comes from St. Augustine, and the elevation of mind resting on God, which has been given to us by St. Bernard, is our contemplatio for today," the Prior told the monks during their Sunday morning period of quiet contemplation. This was a time when all the monks were supposed to sit, without talking, and meditate reflectively upon the Prior's chosen topic.

For Brother Gregory, the simple gazing of the mind in the direction of manifest truth, which was the purpose of the contemplatio, took on a whole new meaning never envisaged by St. Thomas. When the saint had said 'simple intuition of divine truth produces love', he had never been in the position of having only two days to find a saboteur and rescue a friend.

It was late in the morning therefore, after Brother Gregory and Brother Joseph had received permission to miss the second Mass, that they were free to walk into Brno and visit Herr Rosenstrauch's workshop. The Prior was not pleased by their defection, he had a special "Sanctum" planned for his choir that he wanted them all to hear, but the churches were especially full that day with men who were about to go to war, and felt the need of some extra spirituality. So he let the reluctant monks go about their other duties.

"Welcome my friends," Herr Rosenstrauch had greeted them, after the introductions had been completed, "I'm so glad you could join me. Please come into the back. Can I get you some tea?"

Refreshments having been prepared and served the three men settled down in the workshop and Herr Rosenstrauch brought out the small box of microscope lenses that he had been testing for Brother Gregory. "Some of these have proved to be very difficult," he told them, "they are compound lenses made of at least two different types of glass, and they all have very short focal lengths, which makes their testing very difficult on equipment like mine."

"You said 'different types of glass' just now, what do you mean by that? Isn't there only one type of glass?" Brother Joseph asked.

"Goodness, no," laughed the glass cutter, "there are many different types and kinds of glass, it all depends on how it is made. You see, glass is a very strange substance with some most unusual properties."

"In what way?" asked Brother Joseph, who, unlike his colleague had not studied physics at University.

"Well," said Herr Rosenstrauch, warming to this man as any amateur does when asked to talk about his hobby, "most molten materials form crystals when they are allowed cool down slowly from high temperatures, but silica is a rare exception. If the substance, silica is heated to its melting point, about 1723^oC, or 3133^oF, it melts, but, as it cools it remains in an amorphous state and its viscosity increases to such high values it is, for all intents and purposes, a solid."

"You mean that glass is really a liquid?" Lindenthal asked, incredulously.

"Technically it is a liquid but with such high viscosity that it behaves at room temperature like a solid," Rosenstrauch said with a smile, "but pure silica glass has such a high viscosity that, even in the liquid state, is hard to work with."

"Which is why glass manufacturers add other things," said Mendel, anxious to get on.

"They do indeed," proceeded Herr Rosenstrauch, "soda - which has the chemical formula Na₂O - is a common additive, usually in the form of sodium carbonate or nitrate, but this makes the glass soluble in water, which is not one of the more desirable properties." They all laughed at this. "So, to overcome this problem, lime is also added. Most glass, therefore is a mixture of soda, lime and silica."

"Other things are added as well," Mendel said. "various oxides help prevent pitting, fining or decoloration, and even gold is sometimes added to Venetian glass to make it appear red."

"Every change or additive also changes the other properties of glass, such as viscosity, strength, index of refraction, transmission of light, corrosion and even electrical properties, but these latter are only now being investigated," said Rosenstrauch, annoyed that Brother Gregory knew so much. "So you can usually tell one type of glass from another by cataloguing each of these properties."

"Which is why we have come to see you," Mendel insisted, trying to prevent another discourse on the more archaic properties of the material. "Can you tell us anything about these pieces of glass?" He took out his handkerchief and emptied onto the table several shards of the glass he had collected from the guest room fireplace.

None of the pieces were very large, and Rosenstrauch poked them around with his finger for a while, studying them at various angles. He picked one piece up and looked at it more closely through a magnifying glass. "Humm," he said at last, "where did you get these?"

So Mendel told him, which in turn led to the monks giving Herr Rosenstrauch more or less the full story of Brother Matthew and the sabotage in the monastery guest room.

"I see," Herr Rosenstrauch said, scratching his chin, "so these pieces of glass came from what you think is a Krautstrunk Beaker?"

Mendel nodded. "Our guest claimed to have a very old beaker which he inherited from his grandmother, or someone, he said it was an heirloom and he took it everywhere with him. He was most upset when the person who burned his lists also smashed his beaker."

"I can quite understand why," Rosenstrauch said, standing up and going back into the sales area of his shop, which was closed and boarded up for the Sunday holiday. He returned a few moments later carrying a wooden box, the contents of which he sorted through while talking to the monks.

"Those kinds of glass beakers are rare, especially if they are genuine, so they are considered valuable, by some. Whenever something has value, others will try to copy or fake it. There are more phony antiques around than the genuine article, and these beakers are a good example. Here -- " He picked out of his box several large pieces of glass with curious knobbly bumps or warts on the sides of what was once a round glass tube of some sort.

"It is broken, now, but once upon a time someone tried to sell me a fake Krautstrunk beaker that had only been made a few years ago, here in Moravia. It was a good fake, and would have fooled even me, or any other expert. The faker had gone to a lot of trouble to use original glass blowing techniques and had clearly studied the style in some detail. But one thing he got wrong, and this is how I knew it was a fake he was trying to sell me; the glass."

Herr Rosenstrauch picked up the parts of the fake beaker and showed them to the monks. "He did not know how to make the original glass. In the 15th century the Medieval glass makers added potash, made by burning wood, to their silica and lime mixture. This potash gives the glass it's characteristic greenish color, and also its name "Waldglas", or forest glass. Not many fakers know this, so they just add a touch of green dye to regular glass made using regular soda."

"But how can you tell the difference?" Brother Joseph wanted to know.

"Simple, the refractive index is very different. Waldglas has a much lower refractive index than regular glass." He then had to explain to Brother Joseph what a 'refractive index' was.

"So, light bends differently in different types of glass?" Brother Joseph said.

"No, not really bends differently," Rosenstrauch corrected, "just bent to a different extent, which is very characteristic of the glass."

"You can measure this here?" Brother Joseph wanted to know, waving his hand at the optical bench and Herr Rosenstrauch's impressive array of optical equipment.

"Oh, yes," he was told, "I do it all the time. The actual measurements are a little tricky, but once you have all the distances measured, the calculation of the sines of the angles and the refractive index itself is simple mathematics"

Brother Joseph looked hard at Brother Gregory. "So you think that Abbot Napp's nephew was the owner of a fake Krautstrunk Beaker?" he said, pointing to the pieces of broken glass that Mendel had brought. "But why would that make any difference"?

"I'm not sure," Brother Gregory answered him with a frustrated shake of his head. "But whoever broke this beaker did so with considerable force and venom. It feels wrong, somehow. Smash the beaker, I can see that, an attempt to anger and annoy an officer in the army. It is a foolish act, and one not designed to improve the cause of Czech nationalism, but one of frustration and a statement of one's feelings. At that level I can sort of see the point of the act. But then why go on and crush the beaker until it was almost unrecognizable? It doesn't make sense."

"Perhaps the saboteur was going to steal the beaker and hold it to ransom. To get money for his cause. Then, when he picked up the beaker, he saw it was a fake, realized it wasn't worth anything, so he smashed it in the grate." This was Brother Joseph's theory. "I can see why a person might be especially upset under those circumstances."

"Yes," said Herr Rosenstrauch, "that makes sense, except that, if the fake was good, no one could tell unless the glass was tested. A saboteur would not easily know the difference between a fake and a real Krautstrunk."

The discussion was going nowhere, and help for Brother Matthew seemed as far off as when they started.

"I would like to test this glass anyway," Mendel said, when all alternatives had been considered and dismissed.

"Of course," agreed Herr Rosenstrauch, "it will only take a few moments to set up the optical bench for a refractive index measurement." He set about adjusting the rods, clamps, lights and other scales and devices on the oak table. "But," he mused, "I find one thing rather strange. These beakers are very rare, yet in one week I have been involved with two of them. If you remember, Herr Mendel, when you first came to see me with your broken microscope, I had a late customer who, by an odd coincidence, was trying to sell a Krautstrunk beaker. Now, here is the good Abbot's nephew, also with one of these rare items. Strange, don't you think?"