2. If the pressure against a surface be six pounds, ten feet below the surface of a lake, what will be the pressure against the same surface twenty-five feet below the surface?

3. Will the pressure at a given depth be different according to the size of the lake?

4. How could you illustrate this pressure by sinking a bottle in deep water?

VI. Buoyancy of Water.—1. Define by aid of an experiment the buoyancy of water.

2. Make an experiment showing that, while a substance apparently becomes lighter when weighed in water, yet there is no absolute loss of weight.

3. Make an experiment showing that, when anything is weighed in water it will suffer a loss of weight exactly equal to the weight of its own bulk of water.

4. Why will a piece of iron sink in water?

5. Why will a cork float in water?

6. When will a substance neither sink nor swim in water but remain at rest in any part of the liquid?

VII. Comparative Density.-1. What do you mean by the comparative density or specific gravity of a body?

2. A piece of pure gold weighs in air fifty-seven grains and in water fifty-four grains, find its specific gravity.

3. On what occasion and by whom was the discovery made of the method of determining specific gravities?

4. A piece of gold said to be pure weighs seventy-six grains in air and seventy grains in water. Is this gold pure? Give a reason for your reply.

5. A piece of stone weighs 200 grains in air, and 150 grains in water. Another piece of the same stone weighs 560 grains in air, what will it weigh in water?

VIII. Buoyancy of other Liquids.-1. Which has most buoyancy, a heavy or a light liquid?

2. Name a liquid in which iron will float.

3. Can a man float most readily in fresh water or salt?

4. Name a sheet of water in which a man will not easily sink.

IX. Capillarity.

above its level.

.-I. Mention a case in which water will rise

2. Show by an experiment that this rising depends on the attraction of the water for the substance used.

3. Name a substance that has a similar attraction for mercury.

PROPERTIES OF GASES, p. 34.

I. Pressure and Weight of Air.-1. What is the characteristic distinction between a gas and a liquid?

2. Whether is air repelled or attracted by the Earth? Illustrate your reply by an experiment.

3. Describe an experiment showing that some gases are heavier bulk for bulk than air.

4. Describe an experiment showing that some gases are lighter bulk for bulk than air.

5. Does the ocean of air above us press against the Earth just as the ocean of water presses against the sea-bottom?

6. Why is not a piece of paper pressed hard against the table by the weight of air above it? Illustrate your reply by an experiment.

7. Describe an experiment showing that air has buoyancy.

II. The Barometer and its Uses.-I. Describe the barometer.

2. Who invented it?

3. What is the usual height of the barometric mercurial column?

4. Would this column be lengthened or shortened by carrying the barometer to the top of a lofty mountain?

5. What is meant by the Torriceliian vacuum?

6. In what way does the height of the mercurial column in general vary with the weather?

III. Air-pump.-1 What is meant by the words piston, cylinder, vaive?

2. Sketch an air-pump and describe its action.

3. The bell-jar of an air-pump contains 90 cubic inches, while the cylinder contains 10 cubic inches: what proportion of the air will be taken out of the bell-jar after one complete stroke of the piston?

IV. Water-pump, Syphon. .-I. If water instead of mercury were used for a barometer, would the column be longer or shorter ?

2. Approximately speaking, what would be the length of the column of a water barometer?

3. Sketch the common water-pump and describe its action. 4. Why will not this pump work if the distance between the surface of water in the reservoir and the lower valve be greater than 30 feet?

5. Why must the distance of question 4 be altered if the pump is worked on the top of a lofty mountain?

6. Sometimes before using a pump it is necessary to throw a little water upon the piston. What is the object of this? 7. Sketch a syphon and show how to use it.

MOVING BODIES, p. 47.

I. Energy and Work.-1. Is energy a substance, or a mood or affection of a substance?

2 What do we mean when we say a substance is full of energy? 3. Enumerate the most conspicuous cases in which a substance is full of energy.

4. How do we measure energy?

5. What is our unit of work?

6. How much work will be done in raising 5 lbs. 10 feet high against gravity?

7. A cannon pointed vertically upwards fires a ball weighing 200 lbs., which rises 850 feet before it turns. What is the energy of the ball?

II. Work done by a Moving Body.-1. A stone weighing one pound projected upwards with the initial velocity of 32 feet per second will rise 16 feet; how much energy does it contain?

2. If a stone weighing four pounds be projected upwards with the velocity of last question, how high will it rise and how much energy will it contain?

3. If a stone weighing three pounds be projected upwards with the (double) velocity of 64 feet per second, how high will it rise and how much energy will it contain?

4. A cannon-ball discharged with the velocity of 1,000 feet per second will pierce through six planks of oak, through how many similar planks will a similar ball pierce when discharged with the (double) velocity of 2,000 feet per second?

III. Energy in Repose.-I. Is a lion when asleep or at rest totally devoid of energy? If not, what kind of energy has he got? 2. Give an instance showing that a pile of stones may possess energy on account of their position.

3. When is a reservoir of water possessed of energy?

4. What is the kind of energy that a wind-mill makes use of? 5. Specify the advantage which energy of repose has over active energy.

VIBRATING BODIES, p. 52.

I. Vibration-Sound.-1. Give an experimental instance of a moving body that does not change its place as a whole.

2. What is the name given to this peculiar species of motion?

3. Does a vibrating body give a series of blows to the air around it?

4. When this blow reaches our ears what do we call the sensation produced?

II. Noise and Music.-I. Give an instance of a body which deals a single blow to the air.

2. Give an instance of a body which deals a series of blows to the air.

3. What do we call the sensation produced when a single blow strikes the ear?

4. What do we call the sensation produced when a series of blows strike the ear?

5. What is the physical distinction between a deep low note and a shrill high note?

6. Give an instance showing that sound is a species of energy, and is capable of doing work.

III. Motion of Sound through Air.-1. Describe an experiment proving that sound requires air to carry it to the ear.

2. When a cannon gives a blow to the air, are the individual particles of air so struck shot off till they reach the ear of a man at a distance who hears the report?

3. If this be not the case, how is the motion propagated to his ear? Illustrate your reply by an experiment.

4. Give an illustration of this derived from the game of croquet. IV. Its Rate of Motion.- 1. Give a proof that sound requires time to go from a cannon to the ear.

2. At what rate does the sound pass through the air?

3. At what rate will sound pass through water?

4. At what rate will it pass through wood?

5. A man at a distance hears the report of a cannon five-anda-half seconds after seeing the flash, how far is he from the cannon?

V. Reflection of Sound--Echoes.-I. Give a physical explanation of echoes.

2. Describe an experiment showing that sound like light can have a focus.

3. Illustrate the property of sound by reference to a peculiarity of St. Paul's Cathedral in London.

VI. How to find the Rate of Vibration corresponding to a given Note.-1. Sketch and describe an instrument by which we can find the number of vibrations n one second corresponding to any note.

HEATED BODIES, p. 61.

I. Nature of Heat (first notice).-I. Is a hot body heavier than a cold one?

2. Is a hot body possessed of more energy than a cold one?

3. If heat be a species of motion, why does not the eye see the particles of a hot body moving?

4. In vibrating bodies there are two things to be studied, what are these?

5. In heated bodies there are two things to be studied, what are these?

II. Expansion of Bodies when Heated.-I. Describe an experiment showing that a metallic rod becomes longer when heated.

2. What happens when a hollow glass bulb filled with water is heated?

3. What happens when a bladder two-thirds filled with air is heated?

III. Thermometers, and how to make them.-I. Describe generally the instrument called a mercurial thermometer and its mode of action.

2. Describe the method of filling and sealing a mercurial thermometer.

3. Describe the method of graduating a centigrade mercurial thermometer.

4. Why is this instrument called a centigrade thermometer? 5. What is blood-heat on the centigrade scale?

IV. Expansion of Solids, Liquids, and Gases.-I. Whether does glass or lead expand most?

2. Whether does platinum or zinc expand most?

3. Give a proof, by means of the thermometer, that liquids expand more than solids.

4. Do liquids expand more or less rapidly at a high than at a low temperature?

5. Do gases expand more than liquids?

6. Do gases expand from any other cause than heat?

7. If a bladder not completely filled with air have a volume = 1,000 cubic inches at the freezing-point, what will be its volume at the boiling point?

8. Describe an experiment showing that liquids expand with enormous force.

9. Show how the force of contraction due to cooling is made use of in making carriage-wheels.