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 



Oil Immersion Objectives 310 



