Passages from the Life of a Philosopher

point of the old file; then turn the bit of glass over, and scratch on the other side a similar mark exactly opposite to the former. Fix one of the small centre-punches with its point upwards in the vice. Let an assistant gently hold the bit of glass with its scratched point exactly resting upon the point of the centre-punch. Take the other centre-punch in your own left hand and place its point in the centre of the upper scratch, which is of course nearly, if not exactly, above the fixed centre-punch. Now hit the upper centre-punch a very slight blow with the hammer: a mere touch is almost sufficient. This must be carefully repeated two or three times. The result of these blows will be to cause the centre of the cross to be, as it were, gently pounded. {378} Turn the glass over and let the slight cavity thus formed rest upon the fixed centre-punch. Repeat the light blows upon this side of the glass, and after turning it two or three times, a very small hole will be made through the glass. It not unfrequently happens that a small crack occurs in the glass; but with a little skill this can be cut out with the pane of the hammer. The next process is to enlarge the hole and cut it into the required shape with the pane of the hammer. This is accomplished by supporting the glass upon the point of the fixed centre-punch, very close to the edge required to be cut. A light blow must then be struck with the pane of the hammer upon the edge to be broken. This must be repeated until the required shape is obtained. The principles on which it depends are, that glass is a material breaking in every direction with a conchoidal fracture, and that the vibrations which would have caused cracking or fracture are checked by the support of the fixed centre-punch in close contiguity with the part to be broken off. When by hastily performing this operation I have caused the glass to crack, I have frequently, by using more care, cut an opening all round the cracked part, and so let it drop out without spreading. 〈CUTTING A HOLE IN GLASS.〉 This process is rendered still more valuable by the use of the diamond. I usually carried in my travels a diamond mounted on a small circle of wood, so that I could easily cut out circles of glass with small holes in the centre. The description of this process is sufficient to explain it to an experienced workman; but if the reader should wish to employ it, his readiest plan would be to ask such a person to show him how to do it. The above technical description will doubtless be rather {379} dry and obscure to the general reader; so I hope to make him amends by one or two of the consequences which have resulted to me from having instructed others in the art. 〈THE GRATEFUL GLAZIER.〉 In the year 1825, during a visit to Devonport, I had apartments in the house of a glazier, of whom one day I inquired whether he was acquainted with the art of punching a hole in glass, to which he answered in the negative, and expressed great curiosity to see it done. Finding that at a short distance there was a blacksmith whom he sometimes employed, we went together to pay him a visit, and having selected from his rough tools the centre-punches and the hammer, I proceeded to explain and execute the whole process, with which my landlord was highly delighted. On the eve of my departure I asked for the landlord’s account, which was duly sent up and quite correct, except the omission of the charge for the apartments which I had agreed for at two guineas a week. I added the four weeks for my lodgings, and the next morning, having placed the total amount upon the bill, I sent for my host in order to pay him, remarking that he had omitted the principal article of his account, which I had inserted. He replied that he had intentionally omitted the lodgings, as he could not think of taking payment for them from a gentleman who had done him so great a service. Quite unconscious of having rendered him any service, I asked him to explain how I had done him any good. He replied that he had the contract for the supply and repair of the whole of the lamps of Devonport, and that the art in which I had instructed him would save him more than twenty pounds a year. I found some difficulty in prevailing on my grateful landlord to accept what was justly his due. 〈MODESTY REWARDED.〉 The second instance I shall mention of the use to which I {380} turned this art of punching a hole in glass occurred in Italy, at Bologna. I spent some weeks very agreeably in that celebrated university, which is still proud of having had the discoverer of the circulation of the blood amongst its students. One morning an Italian friend accompanied me round the town, to point out the more remarkable shops and manufactories. Passing through a small street, he remarked that there was a very well-informed man who kept a little shop for the sale of needles and tape and a few other such articles, but who also made barometers and thermometers, and had a very respectable knowledge of such subjects. I proposed that we should look in upon him as we were passing through the street. On entering his small shop, I was introduced to its tenant, who conversed very modestly and very sensibly upon various math­e­mat­i­cal instruments. I had invited several of my friends and professors to spend the evening with me at my hotel, for the purpose of examining various instruments I had brought with me. I knew that the sight of them would be quite a treat to the occupier of this little shop, so I mentioned the idea to my friend, and inquired whether my expected guests in the evening would think I had taken a liberty with them in inviting the humble constructor of instruments at the same time. My friend and conductor immediately replied that he was well known to most of the professors, and much respected by them, and that they would think it very kind of me to give him that opportunity of seeing the instruments I possessed. I therefore took the opportunity of asking him to join the very agreeable party which assembled in my apartments in the evening. 〈PRETENSION REPRESSED.〉 We now made a tour of the city, and reached the factory {381} of the chief philosophical instrument-maker of Bologna. He took great pleasure in showing me the various instruments he man­u­fac­tured; but still there was a certain air of presumption about him, which seemed to indicate a less amount of knowledge than I should otherwise have assigned to him. I had on the preceding day mentioned to my Italian friend, who now accompanied me, that there existed a very simple method of punching a hole in a piece of glass, which, as he was much interested about it, I promised to show him on the earliest opportunity. Finding myself in the workshop of the first instrument maker in Bologna, and observing the few tools I wanted, I thought it a good opportunity to explain the process to my friend; but I could only do this by applying to the master for the loan of some tools. I also thought it possible that the method was known to him, and that, having more practice, he would do the work better than myself. I therefore mentioned the circumstance of my promise, and asked the master whether he was acquainted with the process. His reply was, “Yes; we do it every day.” I then handed over to him the punch and the piece of glass, declaring that a mere amateur, who only oc­ca­sion­al­ly practised it could not venture to operate before the first instrument-maker in Bologna, and in his own workshop. I had observed a certain shade of surprise glance across the face of one of the workmen who heard the assertion of this daily practice of his master’s, and, as I had my doubts of it, I contrived to put him in such a position that he must either retract his statement or else attempt to do the trick. 〈AWFUL SMASH.〉 He then called for a flat piece of iron with a small hole in it. Placing the piece of glass upon the top of this bit of iron, and holding the punch upon it directly above the {382} aperture, he gave a strong blow of the hammer, and smashed the glass into a hundred pieces. I immediately began to console him, remarking that I did not myself always succeed, and that unaccountable circumstances sometimes defeated the skill even of the most accomplished workman. I then advised him to try a larger52 piece of glass. Just after the crash I had put my hand upon a heavier hammer, which I immediately withdrew on his perceiving it. Thus encouraged, he called for a larger piece of glass, and a bit of iron with a smaller hole in it. In the meantime all the men in the shop rested from their work to witness this feat of every-day occurrence. Their master now seized the heavier hammer, which I had previously just touched. Finding him preparing for a strong and decided blow, I turned aside my head, in order to avoid seeing him blush—and also to save my own face from the coming cloud of splinters. 52 The larger the piece of glass to be punched the more certainly the process succeeds. I just saw the last triumphant flourish of the heavy hammer waving over his head, and then heard, on its thundering fall, the crash made by the thousand fragments of glass which it scattered over the workshop. I still, however, felt it my duty to administer what consolation I could to a fellow-creature in distress; so I repeated to him (which was the truth) that I, too, oc­ca­sion­al­ly failed. Then looking at my watch, and observing to my companion that these tools were not adapted to my mode of work, I reminded him that we had a pressing engagement. I then took leave of this celebrated instrument-maker, with many thanks for all he had shown me. After such a misadventure, I thought it would be cruel to {383} invite him to meet the learned professors who would be assembled at my evening party, especially as I knew that I should be asked to show my friends a process with which he had assured me he was so familiar. The unpretending maker of thermometers and barometers did however join the party; and the kind and considerate manner in which my guests of the university and of the city treated him raised both parties in my estimation. I will here mention another mode of treating glass, which may oc­ca­sion­al­ly be found worth communicating. Ground glass is frequently employed for trans­mit­ting light into an apartment, whilst it effectually prevents persons on the outside from seeing into the room. Rough plate-glass is now in very common use for the same purpose. In both these circumstances there is a reciprocity, for those who are within such rooms cannot see external forms. 〈ROUGH GLASS MADE TRANSPARENT.〉 It may in some cases be desirable partially to remedy this difficulty. In my own case, I cut with my diamond a small disc of window-glass, about two inches in diameter, and cemented it with Canada balsam to the rough side of my rough plate-glass. I then suspended a circular piece of card by a thread, so as to cover the circular disc. When the Canada balsam