If oil is poured on the water it checks the sound-waves and puts you out.

Question 2.—­What would happen if two sound-waves exactly alike were to meet one another in the open air, moving in opposite directions?

Answer.—­If the sound-waves which meet in the open air had not come from the same source they would not recognise each others existence, but if they had they would embrace and mutually hold fast, in other words, interfere with and destroy each other.

Question 9.—­Describe any way in which the velocity of light has been measured.

Answer (a).—­A distinguished but Heathen philosopher, Homer, was the first to discover this.  He was standing one day at one side of the earth looking at Jupiter when he conjectured that he would take 16 minutes to get to the other side.  This conjecture he then verified by careful experiment.  Now the whole way across the earth is 3,072,000 miles, and dividing p 186this by 16 we get the velocity 192,000 miles a second.  This is so great that it would take an express train 40 years to do it, and the bullet from a canon over 5000 years.

P.S.—­I think the gentlemans name was Romer not Homer, but anyway he was 20% wrong and Mr. Fahrenheit and Mr. Celsius afterwards made more careful determinations.

(b) An Atheistic Scientist (falsely so called) tried experiments on the Satellites of Jupiter.  He found that he could delay the eclipse 16 minutes by going to the other side of the earths orbit; in fact he found he could make the eclipse happen when he liked by simply shifting his position.  Finding that credit was given him for determining the velocity of light by this means he repeated it so often that the calendar began to get seriously wrong and there were riots, and Pope Gregory had to set things right.

Question 10.—­Explain why water pipes burst in cold weather.

Answer.—­People who have not studied p 187Acoustics think that Thor bursts the pipes, but we know that it is nothing of the kind for Professor Tyndall has burst the mythologies and has taught us that it is the natural behaviour of water (and bismuth) without which all fish would die and the earth be held in an iron grip,

CHAPTER VIII.

FOREIGNERS’ ENGLISH.

IT is not surprising that foreigners should make mistakes when writing in English, and Englishmen, who know their own deficiencies in this respect, are not likely to be censorious when foreigners fall into these blunders.  But when information is printed for the use of Englishmen, one would think that the only wise plan was to have the composition revised by one who is thoroughly acquainted with the language.  That this natural precaution is not always taken we have ample evidence.  Thus, at Havre, a polyglot announcement of certain local regulations was posted in the harbour, and the notice stood as follows in French:  ``Un arrangement peut se faire avec le pilote pour de promenades a! rames.’’ The following very strange translation into p 189English appeared below the French:  ``One arrangement can make himself with the pilot for the walking with roars.’’