_Question_ 27.--Account for the delicate shades of colour sometimes seen on the inside of an oyster sh.e.l.l. State and explain the appearance presented when a beam of light falls upon a sheet of gla.s.s on which very fine equi-distant parallel lines have been scratched very close to one another.

_Answer_.--The delicate shades are due to putrefaction; the colours always show best when the oyster has been a bad one.

Hence they are considered a defect and are called chromatic aberration.

The scratches on the gla.s.s will arrange themselves in rings round the light, as any one may see at night in a tram car.

_Question_ 29.--Show how the hypothenuse face of a right-angled prism may be used as a reflector. What connection is there between the refractive index of a medium and the angle at which an emergent ray is totally reflected?

_Answer_.--Any face of any prism may be used as a reflector. The connexion between the refractive index of a medium and the angle at which an emergent ray does not emerge but is

totally reflected is remarkable and not generally known.

_Question_ 32.--Why do the inhabitants of cold climates eat fat? How would you find experimentally the relative quant.i.ties of heat given off when equal weights of sulphur, phosphorus, and carbon are thoroughly burned?

_Answer_.--An inhabitant of cold climates (called Frigid Zoans) eats fat princ.i.p.ally because he can't get no lean, also because he wants to rise is temperature. But if equal weights of sulphur phosphorus and carbon are burned in his neighbourhood he will give off eating quite so much. The relative quant.i.ties of eat given off will depend upon how much sulphur etc. is burnt and how near it is burned to him.

If I knew these facts it would be an easy sum to find the answer.

1881.

_Question_ 1.--Sound is said to travel about four times as fast in water as in air.

How has this been proved? State your reasons for thinking whether sound travels faster or slower in oil than in water.

_Answer_(_a_).--Mr. Colladon, a gentleman who happened to have a boat, wrote to a friend called Mr. Sturm to borrow another boat and row out on the other side of the lake, first providing himself with a large ear-trumpet. Mr. Colladon took a large bell weighing some tons which he put under water and hit furiously. Every time he hit the bell he lit a fusee, and Mr.

Sturm looked at his watch. In this way it was found out as in the question.

It was also done by Mr. Byott who sang at one end of the water pipes of Paris, and a friend at the other end (on whom he could rely) heard the song as if it were a chorus, part coming through the water and part through the air.

(_b_) This is done by one person going into a hall (? a well) and making a noise, and another person stays outside and listens where the sound comes from. When Miss Beckwith saves life from drowning, her brother makes a noise under water, and she hearing the sound some time after can calculate where he is and dives for him; and what Miss Beckwith can do under water, of course a mathematician can do

on dry land. Hence this is how it is done.

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

this 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...o...b..t; 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

Acoustics 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 bis.m.u.th) 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

English appeared below the French: ''One arrangement can make himself with the pilot for the walking with roars.''

The papers distributed at international exhibitions are often very oddly worded.

Thus, an agent in the French court of one of these, who described himself as an ''Ancient Commercial Dealer,'' stated on a handbill that ''being appointed by Tenants of the Exhibition to sell Show Cases, Frames, &c., which this Court incloses, I have the honour to inform Museum Collectors, Librarians, Builders, Shopkeepers, and business persons in general, that the fixed prices will hardly be the real value of the Gla.s.ses which adorn them.''

In 1864 was published in Paris a pretentious work, consisting of notices of the various literary and scientific societies of the world, which positively swarms with blunders in the portion devoted to England.

The new forms into which well-known names are transmogrified must be seen to be believed. Wadham College is printed _Washam_, Warwick as _Worwick_; and one of our metropolitan parks is said to be

dedicated to a saint whose name does not occur in any calendar, viz., _St. Jam's Park_. There is the old confusion respecting English t.i.tles which foreigners find so difficult to understand; and monsieur and esquire usually appear respectively before and after the names of the same persons. The Christian names of knights and baronets are omitted, so that we obtain such impossible forms as ''Sir Brown.''

The book is arranged geographically, and in all cases the English word ''shire''

is omitted, with the result that we come upon such an extremely curious monster as ''le Comt de Shrop.''On the very first page is made the extraordinary blunder of turning the Cambrian ArchThe Roxburgh Society, although its foundation after the sale of the magnificent library of the Duke of Roxburgh is correctly described, is here placed under the county of Roxburgh. The most amusing blunder, however, in the whole book is contained in the following charmingly nave piece of etymology _tre penser, ds le dbut, qu'il s'agit d'une Socit hippique. II n'en est rien; The Germans find the same difficulty with English t.i.tles that the French do, and confuse the Sir at the commencement of our letters with Herr or Monsieur.Thus, they frequently address Englishmen as _Sir_, instead of mister or esquire. We have an instance of this in a publication of no less a learned body than the Royal Academy of Sciences of Munich, who issued in 1860 a ''Rede auf Sir Thomas Babington Macaulay.''An hotel-keeper at Bale translated ''limonade gazeuse'' as ''gauze lemonads"; and the following delightful entry is from the Travellers' Book of the Drei Mohren Hotel at Augsburg, under date Jan. 28th, 1815: ''His Grace Arthur Wellesley, Duke of Wellington, &c., &c., &c. Great honour arrived at the beginning of this year to the three Moors. This ill.u.s.trious warrior, whose glorious atchievements which cradled in Asia have filled Europe with his renown, descended in it.''It may be thought that, as this is not printed, but only written, it is scarcely fair to preserve it here; but it really is too good to leave out.The keepers of hotels are great sinners in respect to the manner in which they murder the English language. The following are a few samples of this form of literature, and most readers will recall others that they have come across in their travels.The first is from Salzburg:-- ''George Nelbck begs leave to recommand his hotel to the Three Allied, situated _vis- The next notice comes from Rastadt:-- ''ADVICE OF AN HOTEL.''The underwritten has the honour of informing the publick that he has made the acquisition of the hotel to the Savage, well situated in the middle of this city.He shall endeavour to do all duties which gentlemen travellers can justly expect; and invites them to please to convince themselves of it by their kind lodgings at his house.''BASIL ''JA. SINGESEM.''Before the tenant of the Hotel to the Stork in this city.''Whatever may be the ambition of mine host at Pompeii, it can scarcely be the fame of an English scholar:--