CONTENTS. 15 



CHAPTER V. 



Illumination 183 



Sunlight 186 . 



Artificial Light ' 187 



CHAPTER VI. 



Choice of Objectives for Regular Work . . . 202 



Selection of Covering Glass 213 



Bull's Eye Condenser 225 



Working with Low Powers 225 



The Spencer one-inch of 50 Broad Guage Objectives, 



etc. 230 



CHAPTER VII. 



Work with the Higher " Powers " 235 



Position of Observer 246 



Mean of ten Measurement of Moller Test Plates . .253 



Position of Observer ....... 289 



Work over dry Mounts with high Aperture Objectives . 298 



Oil Immersion Object Glasses ....' 309 



New Oil Immersion Objectives 310 



