96 PRACTICAL MICROSCOPY. 



Dr. Woodward prefers to use the ammonia-sulphate of 

 copper cell, and then only for high power definition, and he 

 says he has been able to resolve the markings on Amphi- 

 pleura pellucida with objectives found incapable of doing it 

 with white light. Professor Smith, of Ashtabula, also 

 expresses his approval of the use of monochromatic light. 

 He says that with its use, and an eighth dry objective, he 

 has easily resolved the A. pellucida to beads, in balsam, 

 with deep eye-pieces ; and with the lowest eye-piece the 

 transverse and longitudinal striae were easily seen. 



The white cloud illuminator is a contrivance made in 

 order to produce the same kind of illumination from 

 artificial light as is obtainable from a white cloud. It is 

 generally used with low powers only, and is made in 

 several ways a concave surface of plaster of Paris, a 

 mirror coated at the back with zinc-white paint, roughened 

 enamel, and white paper have all been used to produce 

 this effect, as well as the disc of ground glass found in 

 Mr. Collins's light-modifier. 



Thus closes the chapter on accessories; but the student 

 must not think we have exhausted the subject : there are 

 many pieces of apparatus in occasional use which it has not 

 been thought necessary to include here, and many others 

 will be described in the subsequent chapters under the 

 headings in which they are more intimately concerned. 



