(4) Describe in detail experiments to prove that bodies transparent to light may absorb invisible radiations in very different degrees. (S. & A. Adv., 1896.)

(5) State Prevost's theory of exchanges, and show how it follows from the theory that the radiating and absorbing powers of a surface at a given temperature are the same. (S. & A. Adv., 1894.)

(6) Describe the most important experimental results on the absorption of radiation by gases. (S. & A. Adv., 1894.)

(7) How would you propose to determine the quantity of radiant heat received from the sun on a square inch on the earth's surface? (Sen. Camb. Local, 1897.)

(8) What is meant by the theory of exchanges?

Account for the fact that good radiators are also good absorbers. (Sen. Oxf. Local, 1896.)

(9) Describe any method by which the rate of radiation received from the sun has been determined. State briefly the reasons for the conclusion that all the radiation measured is of one kind, differing only in wave-length. (Lond. Univ. B.Sc. Pass, 1896.)

(10) State Prevost's theory of exchanges. Describe and discuss experiments which illustrate it. (Lond. Univ. Inter. Sci. Hon., 1894.) (11) Describe experiments which have been made to determine the law of radiation from heated surfaces.

Give an account of some method by which it has been sought to measure the temperature of the radiating surface of the sun.

Univ. B.Sc. Hon., 1894.)

(Lond.

(12) A wire 1 cm. in diameter, carrying a current of 10 ampères, is found to reach a steady temperature of 100° C. Assuming the specific resistance of the material as 2'1 × 10 ohms per cm. cube, and the value of J as 42 × 10 ergs, determine the amount of heat emitted at 100° C. by a square centimetre of the surface. (S. & A. Hon. I., 1899.)

PRACTICAL.

(1) Given a Leslie cube, a thermopile, and a galvanometer, find the relation between the radiation from the cube, and the excess of temperature above the surroundings. (Inter. Sci. Hon., July, 1895.)

(2) Measure and plot the radiation of a tin of boiling water at different distances from a given thermopile. (Inter. Sci. Hon., 1897.)

(3) Compare the radiating powers of two given surfaces by means of a thermopile. (B.Sc. Pass and Hon., 1897.)

MISCELLANEOUS EXAMPLES

(1) Show in a general manner that according to the kinetic theory of gases the pressure is proportional to the mean kinetic energy of agitation, and establish Avogadro's law as a consequence of the theory. (S. & A. Hon. I., 1898.)

(2) Show how to obtain the gaseous laws of Boyle, Charles, and Avogadro from the principles of the kinetic theory of gases. (S. & A. Hon., 1895.)

(3) Obtain a formula giving the value of J in terms of the pressure, temperature, and density of a mass of gas, and the difference between its two specific heats. What experiments are necessary to justify the assumption made in obtaining the formula? (S. & A. Hon., 1895.)

(4) Explain how the thermal equivalent of mechanical energy may be derived from a knowledge of how much heat is required to warm a given quantity of gas a given number of degrees, first when pressure on it is kept constant, and next when it is heated in a closed inexpansible vessel. (S. & A. Hon., 1889.)

(5) What is meant by an isothermal curve? Indicate the form of such a curve (1) for a gas, (2) for a vapour, tracing the curve in the latter case from the condition of unsaturated vapour to that of complete liquefaction, and explain how the work done in compressing the gas or vapour may be represented in either case. (Univ. Coll. Lond.,

1897-1898.)

(6) Define the terms work, force, pressure. Show that if a piston is moved along a cylinder against a constant pressure, the work done in a stroke is equal to the product of the pressure into the volume swept out by the piston. Explain clearly the units in which the work will be given by this calculation. (Lond. Univ. Inter. Sci. Pass, 1897.)

(7) Prove that the ratio of the two specific heats of a gas at constant pressure and volume respectively is the same as the ratio of its adiabatic and thermal elasticities. (S. & A. Hon. II., 1898.)

(8) Find the equation of an adiabatic of a refractory gas, such as air, (S. & A. Hon., 1896.)

(9) What are the properties which determine the velocity of sound in a solid, a liquid, or a gas? Explain why Newton's value of the velocity of sound in air differs from the true value. Calculate the Newtonian velocity of sound in a gas whose density at standard pressure and temperature is 1 kilogram per cubic metre. What would you expect

the true velocity to be? (S. & A. Hon., 1891.)

(10) If a quantity of air at 15° C. is suddenly compressed to half its volume, show how to calculate the temperature it will momentarily attain. Explain the importance of this knowledge in the theory of sound propagation. (S. & A. Hon., 1889.)

(11) What effect does pumping half the air out of a closed vessel produce on the velocity of sound passing through it? Also, what is the effect of compressing the air? (The temperature in both cases is supposed to be constant.) (S. & A. Adv., 1888.)

(12) The specific gravity of a certain gas, under a pressure of 75 metres of mercury at o° C., is one-thousandth that of water. What is the velocity of sound in it at that temperature? What is it also at the temperature 100°? Examine whether altering the pressure on the gas will affect the velocity. (Take the ratio of the two specific heats as 14.) (S. & A. Hon., 1888.)

(13) How does the velocity of sound through different gases at the same temperature and pressure depend upon the density of the gas? Describe a simple experiment by which you could prove that the velocity of sound through coal-gas is not the same as the velocity through air. (Inter. Sci. Pass, July, 1895.)

(14) Describe the various methods employed to determine the ratio of the specific heats of gases. What inference as to the constitution of the molecule of the gas is sometimes drawn from these measurements? (B. Sc. Hon., December, 1895.)

(15) Explain the possibility of the artificial production of cold by the performance of mechanical work on a suitable substance. If ordinary dry air at ten atmospheres is suddenly released, explain how the reduction of temperatures can be calculated. (Final Pass, B.Sc. Vict. Univ., 1898.)

(16) What is meant by the statement that the specific heat of saturated steam at 100° is negative ?

Assuming that steam obeys the gas laws, show that the work done in changing the volume of 1 gram of steam at 100° and 760 mm. to the volume of 101 and 787 mm. (the saturation pressure at 101°), is more than sufficient to supply the heat needed for the rise in temperature, the specific volume of steam at 100 being taken at 1,700, and its specific heat at constant pressure as o'48. (Lond. Univ. B.Sc. Hon., 1891.)

APPENDIX

THE WET AND DRY BULB HYGROMETER.

This table gives the pressure, in mm. of mercury, that would be exerted by the
aqueous vapour in the atmosphere when cooled to the dew point; the dry bulb
reading being t° C, and the difference between the dry and wet bulb readings being
equal to the respective numbers in the top line.

(Compiled from Table 170, Smithsonian Physical Tables.)

16°3 14.9 1324

20

22

17'4 15'9 14'3
18'5 16'9 15'3
19'7 18'0 16'4 14'8

12'9

8'1 6'9 5'7 4'6
8'8 7'6

6'4 5'2

13.8

23

20'9

24

22'2

25

26

23'5 21'7
25'0 23'1

27 26'5 24'5

12'4 II'O 9'6 8'4 7'1 5'9
133 11'9 10'5 9'1 7.8 6'6
19'2 17'5 15'9 14 3
12'8 11'3 10'0 8.6
20'4 18.6 17'0
15'3
13'8 12'3 10'9
19'9 18'1 16'4 14'8 13'3 11.8
21'I 19'4 17'6 15'9

28

28'1 26'0 24'0 22'0 20'I 18'3
27'6
25'5 23'5 21'5 19'6
31'5 29'3 27'1 25'0 22'9 21'0

16'6

14'9 13°3 11.8
17'8 16'1 14'4
19'1

10'2

128

11 2

17'3 15'5

13'9

12'3

H H

MAXIMUM PRESSURE OF AQUEOUS VAPOUR AT DIFFERENT TEMPERATURES.

Deduced by Broch from Regnault's Experimental Data.

(The pressure is given in mm. of mercury, at o° C, and at the sea level in lat. 45°.)

VOLUME, IN C.CS., OCCUPIED BY 1 GRAM OF WATER AT VARIOUS TEMPERATURES (Rosetti).