1875.] Notices of Books. 263 
being opened the water falls, gaining velocity as it loses height. 
3. The falling water encounters a water-wheel, and gives up to 
it some of its motion, the wheel in its turn giving motion to a 
system of machinery. 4: Heat is produced both by the clash of 
the falling water and by the friction of the bearing parts of the 
machinery; or millstones. 5. The millstones, working in a 
vessel of water, raise it to the boiling-point. 6. But no higher, 
for the water then passes into steam. 7. The steam so gene- 
rated may work a steam-engine. 8. Which may work an elec- 
trical machine. 9g. By which we may produce, through the 
intervention of the spark, both light and heat. 10. Or may de- 
compose water. 11. While; finally, the liberated oxygen and 
hydrogen may be re-composed, and the steam produced may 
work a pump and replenish the head of water in the original 
reservoir. ‘‘ Our proposition then is,” says the Author, “ that 
we may represent numerically—(1) the power to produce changes 
which the water in the reservoir has in virtue of its quantity, 
and its height above the mill-wheel ; (2) how much of the power 
due to motion the water gains as it loses height in falling ; 
(3) how much in motion, and how much in heat it gives to itself 
and to the mill-wheel when it clashes on it ; (4) how much heat 
goes to turn water into steam; (5) what the steam loses in 
working the steam-engine; (6) how much the steam-engine is 
retarded by working the electric machine, and producing heat; 
and decomposing the water.”” ‘Then comes a section on funda- 
mental units; mass and force, velocity, &c.; then the second 
and third laws of motion; the measurement of heat; and the 
measurement of work done. The second section treats of dy- 
namical energy; the third of thermal and other energies,—elec: 
trical, chemical, and what he calls ‘‘ animal energy,” and the 
energy of vegetation ; while a short section at the end treats of 
molecular theories. The work is very sound and clearly con- 
structed, and we recommend it to the student as a very useful 
book on a very important subject. 
The Elements of the Psychology of Cognition. By RoBert 
JarpinE, B.D., D.Sc., Principal of the General Assembly’s 
College, Calcutta, and Fellow of the University of Calcutta. 
London: Macmillan and Co. 1874. 
Tuts work is designed for the use of students who are beginning 
the study of philosophy, and its object is to serve as an intro- 
duction to the psychology of the intellectual part of the human 
mind. After an introductory chapter, we have chapters on the 
acquisition of presentative knowledge, on the theories of percep- 
tion, on representation, and a final chapter on the elaboration of 
knowledge. In the latter some useful matter concerning in- 
duction and deduction may be found :—‘‘ Induction proper has 
VOL. V. (N.S.) re te 
