Page:Passages from the Life of a Philosopher.djvu/393

Rh reputation of knowing everything that I was led to inquire into the probable grounds of the egregious fallacy. The most frequent symptom was an address of this kind:—"Now Mr. Babbage, will you, who know everything, kindly explain to me — — — ." Perhaps the thing whose explanation was required might be the metre of some ancient Chinese poem: or whether there were any large rivers in the planet Mercury.

One of the most useful accomplishments for a philosophical traveller with which I am acquainted, I learned from a workman, who taught me how to punch a hole in a sheet of glass without making a crack in it.

The process is very simple. Two centre-punches, a hammer, an ordinary bench-vice, and an old file, are all the tools required. These may be found in any blacksmith's shop. Having decided upon the part of the glass in which you wish to make the hole, scratch a cross (X) upon the desired spot with the 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.