37 
[Four of these eight .] 
1. Supposing you were required to demonstrate experimentally 
the law that like electricities repel, and that unlike electricities 
attract, each other, how would you do it ? 
2. You are furnished with a stick of sealing wax and a piece 
of flannel, and are required with these to charge a gold leaf 
electrometer with positive electricity ; how will you do it ? 
3. Give a brief sketch of the theory of electric fluids, and illus- 
trate the theory by applying it to a clearly described case of 
electric induction. 
4. State what you know regarding the distribution of elec- 
tricity on the surfaces of conductors, both spherical and elongated ; 
give a scientific explanation of the action of pointed lightning- 
conductors, and state the reason why lightning is so destructive 
to trees and buildings, while a metallic rod allows it to pass 
harmlessly away. 
5. Describe and explain the electrophorus. 
5. Describe and explain the Leyden jar. 
7. Describe and explain the plate glass electric machine, and 
state precisely how the prime conductor is charged when the 
plate is caused to rotate between its cushions. 
8. If you wished to fire a mine by the spark from a Leyden 
jar, what precautions would you take to secure the ignition 
of the gunpowder ? State j our reasons for the precautions which 
you would adopt. 
Afternoon Paper. 
[Three of these seven.] 
1. Give a drawing and a description which shall clearly illus- 
trate the action of the hydraulic press. 
2. Describe and explain the action of the great Geyser of 
Iceland. 
3. Describe and explain the action of the common pump or 
common fire-engine. 
4. How do you suppose sound to be propagated through the 
atmosphere ? State its velocity in air, water, and some other 
substance ; how is its velocity in air affected by temperature ? 
Add, if you can, an explanation of the discrepancy between 
N ewton's first calculation and the observed velocity of sound. 
5. On what does the production of a musical sound depend ? 
On what does the pitch of a note depend ? Describe an instru- 
