ZOOLOGY AND BOTANY, MICROSCOPY, ET£1. 



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will be indistinct and fragmentary. This will also occur if the edges 

 of tlie slit are defective or if particles of dust have got in. In the 

 case we are considering it is caused by the sharp outlines of the blood- 

 corpuscles. If the Microscope is placed out of focus a uniformly 

 bright spectrum will be obtained with sharp Fraunhofer lines, and 

 the distinct absorption-bands of the haemoglobin. A band of the 



FiCx. 43. 



Fig. 45. 



sharp image of the object is of course no longer spectrally analysed, 

 but only a band of the circles of confusion, which now fall in the 

 plane of the slit, forming there an indistinct image of the corpuscles. 

 We have, however, in this way, removed the injurious action of their 

 sharp outlines upon the clearness of the absorption spectrum.* 



* Besides the value of the spectroscopic eye-piece for the study of absorption- 

 spectra, Dr. Eollet mentions the use he has made of it in the examination of 

 Newton's rings, and the polarization colours of crystalline plates. 



Ser. 2.— Vol. Ill- T 



