SCIENCE IN SECONDARY SCHOOLS. 169 
Discussion of results leads to distinction between weight and mass, to the 
idea of change of momentum as the measure of the dynamical action of bodies 
upon one another, and to the principle of conservation of momentum. 
Alternative measure of force (hitherto measured in terms of weight) as rate 
of change of momentum. The poundal and dyne. 
Weight as rate of change of momentum. Newton’s Law of Gravitation. 
His verification by calculation of rate of fall of moon. 
3. A suspended ball is made to swing through a constant vertical distance 
along various curves, and to collide directly with a stationary suspended ball. 
Measurements show that the velocity immediately before impact depends entirely 
on vertical distance fallen. Connection of result with Principle of Work 
(Second Year, II., C., 5). Kinetic energy. Apparent loss of energy in collisions 
(considered in connection with D., 4). 
D. Physics. 
1. Revision and extension of Second Year work on radiation and conduction. 
Graphic study of temperatures at points on a bar heated (i) steadily (Forbes), 
(ii) rhythmically (Angstrom), to illustrate measurement of conductivity and 
seasonal temperature-changes of soil. 
2. Solar radiation : its fundamental importance. Separation by prism into 
light and dark radiation. Intensity of radiation: law of inverse squares; 
photometry; the cosine-law; Newton’s law of cooling. Influence of character 
of radiating and absorbing material; the incandescent gas-mantle, &c. Absorp- 
tion and reflection of light and dark radiation. Laws of reflection: plane and 
curved mirrors. Applications: periscope, searchlights, lighthouses, &c. The 
sine-law of refraction; indices of refraction. 
3. Heat as a measurable quantity. Study of the temperature-changes of 
variable weights of water heated for the same period by a constant flame leads 
to the formula H=W+t, where W is the weight of water, ¢ the rise of tempera- 
ture, and H the number of ‘calories’ represented by the heating. Repetition 
with other liquids (e.g. linseed oil, glycerine) leads to the more general formula 
H=sW¢, where s is a constant for each substance (the ‘specific heat’). Con- 
firmation by ‘ the method of mixtures.’ Measurements of specific heat. 
Latent heat. Rough determination of latent heat of steam by Black’s 
method, of water by method of mixtures. 
4, Temperature-changes of gases under the conditions (i) of constant pres- 
sure and (ii) of constant volume. Absolute temperature. 
Cooling and heating of gases by adiabatic expansion and compression. 
Applications of results in meteorology. Equivalence of the heat-change to work 
done. Joule’s experiments, &c. Internal-combustion engines. Liquefaction of 
gases; cold storage, &c. 
5. Vapour pressure. Variations of boiling-point with pressure. Steam- 
engines (cylinder and turbine). Uses of superheated steam (in engines, in 
chemical industries, &c.), and of subheated steam (concentration of beet sugar). 
6. Electric:ty : a preliminary course of work, almost entirely qualitative in 
character ; the quantitative aspect of the subject being reserved for study in the 
Fourth Year. Examination of an electric-bel! circuit as a type of electro- 
magnetic mechanism. Analysis of magnetic effects of the current : Oersted’s 
experiment, Maxwell’s screw rule. Industrial and other uses of electro-magnets. 
The electric telegraph. Magnetic effect as an index of current strength; the 
galvanometer. Preliminary notions of voltage and resistance. 
Tlie electric bell as a motor; elaboration of the same principles in the motors 
used for locomotion and power. 
Faraday’s experiments on electro-magnetic induction. The induction coil. 
The dynamo; the ‘magneto’; reciprocal relation between the principles of the 
motor and dynamo; conversion of mechanical into electrical energy, and of 
electrical into mechanical. The telephone. 
Conversion of electrical energy into heat; the incandescent and are lamps ; 
the electric furnace. : rf 
Electrolysis ; industrial applications. Secondary batteries : relation with 
