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SUMMARY OF CURRENT RESEARCHES RELATING TO 



lines, circles, or patterns, can be facilitated in the following way : — 

 Draw with a pen and ink cross lines, or circles, or any other figure 

 required, on the surface of the plane mirror of the Microscope, then 

 focus down until the image of these lines is seen on the upper surface 

 of the top lens of the condenser. By means of a mechanical finger, or 

 of a steady hand with a rest, no difficulty will be experienced in 

 placing the objects in perfectly regular order. 



Holman's Compressorium and Moist Chamber. — Mr. D. S. 

 Holman's new compressor is shown in Fig. 25. The following 

 description is transcribed verbatim from the original : * — 



" This apparatus differs from all other compressors in being so 

 arranged that the mica cover is fixed and immovable, while the lower 

 thicker plate of glass is moved up and down by means of a screw nut 

 and spiral spring, an arrangement which enables the student to adjust 

 the apparatus so as to apply with certainty any degree of pressure 



Fig. '25. 



upon any soft object without risk of breaking large and expensive 

 cover-glasses, crushing the object unexpectedly, or injuring high- 

 power lenses. The writer by its means was enabled to study with 

 great deliberation and certainty the internal anatomy of the larva of 

 the plumed crane-fly (Corethra plumicornis). In this case the pressure 

 could be so nicely adjusted as not to disturb in the slightest degree 

 the normal physiological actions of the larval fly ; the physiological 

 action of the heart could be readily studied, as well as the significance 



* John A. Ryder, in the ' Journal of the Franklin Institute,' 1880. 



