838 Transactions of the Society. 



of the flame is seen nearly in the plane of the object. The object- 

 slide is placed in immersion contact with the plate a under the 

 clips ; the brass plate D will now rotate the object-slide to the 

 required position with reference to the incident light, while the 

 rotation of the Microscope stage (carrying the illuminator) will 

 give every range of obliquity from central light to dark-field with 

 any objective, the lamp and condenser remaining stationary. 



It would doubtless be possible to dispense with a rotatory stage 

 by inserting the glass plate A into a rotating plate in the foot- 

 plate C, but there would be difficulty in making the rotation exactly 

 concentrical to the rotation of the brass object-plate D. 



My acknowledgments are due to Professor Abbe for the interest 

 he has shown in the practical development of the plan : without 

 his assistance even this experimental device would probably not 

 have been made. 



