GENERAL CONSIDERATIONS. 17 



5. Condensers and safety valves. 



6. Thermostats, (i) by regulation of gas ; (2) by boiling 

 a liquid of known composition. 



7. Thermometers. Pyrometers, Thermoelectric Pile, Sie- 

 mens' resistance thermometer ; Calorimeters. 



8. Standard temperatures : as those of melting ice, 



boiling water, &c. 



. 



For electric phenomena 



i. Electric- machines, factional machine, electrophorus, 



Holtz' machine ; ^ voltaic batteries, thermo-electric 



batteries, magneto-electric machines. 

 2. Wires and other metallic conductors; armatures of 



magnets. 

 3. Insulators. 

 4. Leyden jars and other " condensers;" secondary batteries 



or cells of polarization ; magnets, and electro-magnets. 

 5. Rheostats, lightning conductors, &c. 

 6. Guthrie's voltastat, regulators of electric lamps, &c. 

 7. Electroscopes and electrometers, Coulomb's torsion 



balance, voltameters, galvanometers and electrody- 



namometers, magnetometers. 

 8. Standards of resistance, capacity, electro-motive force, 



&c., as the Ohm, the microfarad, L. Clark's voltaic 



constant cell. 



From the physical, as distinguished from the physiological point 

 of view, the science of Acoustics relates to the excitement of 

 vibrations and the propagation of waves in solids, liquids, and 

 gases, and that of Optics to the excitement of vibrations, and the 

 propagation of radiation, in the luminiferous medium. 



From the physiological point of view, only those waves in 

 ordinary matter are considered which excite in us the sensation of 

 Sound, though waves which do not excite this sensation can be 

 detected and studied by appropriate methods. 



