39 
thin films of uncrystallized bodies. In the case of a film of 
crystallized sulphate of lime, how is the retardation necessary to 
interference produced ? 
[ F our of these eight ] 
1. Describe the construction and graduation of an ordinary 
mercurial thermometer. 2d. Show how the degrees of F. D. 
Reaumur may be converted into one another. 
2. What is meant by the co-efficient of expansion ? You are 
required to describe the construction and principle of the gridiron 
pendulum. 
3. A candle placed at the top of the open doorway of a room 
containing a large fire, has its flame blown outwards ; if placed 
at the bottom the flame is blown inwards ; account for these 
effects, and apply them to the explanation of trade winds. 
4. What do you understand by vapour of 110? What by the 
condensation ? What is meant by congellation of water ? State 
all that occurs as regards heat when water passes from solid to 
liquid state, and from liquid to vaporous. 
5. How is the conductivity of bodies for heat to be determined ? 
If we wish to preserve pumps and fountains in frosty weather, 
we surround them by straw. If we wish to preserve ice from 
melting in summer we surround with straw and flannel ; why ? 
Explain the action of clothing in keeping the body warm. 
6. Give a clear statement of the theory of dew, and explain 
how ice is sometimes formed when the temperature of the air a 
few feet above the earth's surface is several degrees above the 
freezing point of water. 
7- Illustrate by some striking instances the different degrees in 
which heat is radiated arid absorbed by different bodies ; give 
also a few instances of the different transparency of bodies for 
radiant heat. 
8. In investigating the diathermancy of gases and vapours, it 
was found necessary to stop the ends of the tube containing 
them by plates of rock salt ; why would not glass answer ? 
State, as far as you can remember, the action of gases and 
vapours upon radiant heat. 
[4 of these 8. ] 
1. You are required to describe some simple means of gene- 
rating a voltaic current ; state the direction in which the current 
flows in the arrangement which you propose ; and state also 
what you mean by the direction of the current. 
