Question 3.—­What is the reason that the hammers which strike the strings of a pianoforte are made not to strike the middle of the strings?  Why are the bass strings loaded with coils of wire?

Answer.—­Because the tint of the clang would be bad.  Because to jockey them heavily.

Question 4.—­Explain how to determine the time of vibration of a given tuning-fork, and state what apparatus you would require for the purpose.

Answer.—­For this determination I should require an accurate watch beating p 177seconds, and a sensitive ear.  I mount the fork on a suitable stand, and then, as the second hand of my watch passes the figure 60 on the dial, I draw the bow neatly across one of its prongs.  I wait.  I listen intently.  The throbbing air particles are receiving the pulsations; the beating prongs are giving up their original force; and slowly yet surely the sound dies away.  Still I can hear it, but faintly and with close attention; and now only by pressing the bones of my head against its prongs.  Finally the last trace disappears.  I look at the time and leave the room, having determined the time of vibration of the common ``pitch’’ fork.  This process deteriorates the fork considerably, hence a different operation must be performed on a fork which is only lent.

Question 6.—­What is the difference between a ``real’’ and a ``virtual’’ image?  Give a drawing showing the formation of one of each kind.

Answer.—­You see a real image every morning when you shave.  You do not see virtual images at all.  The only people who see virtual images are those people p 178who are not quite right, like Mrs. A. Virtual images are things which don’t exist.  I can’t give you a reliable drawing of a virtual image, because I never saw one.

Question 8.—­How would you disprove, experimentally, the assertion that white light passing through a piece of coloured glass acquires colour from the glass?  What is it that really happens?

Answer.—­To disprove the assertion (so repeatedly made) that ``white light passing through a piece of coloured glass acquires colour from the glass,’’ I would ask the gentleman to observe that the glass has just as much colour after the light has gone through it as it had before.  That is what would really happen.

Question 11.—­Explain why, in order to cook food by boiling, at the top of a high mountain, you must employ a different method from that used at the sea level.

Answer.—­It is easy to cook food at the sea level by boiling it, but once you get above the sea level the only plan is to fry it in its own fat.  It is, in fact, impossible to boil water above the sea level by any p 179amount of heat.  A different method, therefore, would have to be employed to boil food at the top of a high mountain, but what that method is has not yet been discovered.  The future may reveal it to a daring experimentalist.