^^oumli^FeTrisTa'] NOTES AND BIEMORANDA. 103 



retina and on other portions of the object. Now, all these effects will 

 not show us its true structure, but will rather contribute to a false 

 impression of what is under examination. From such considerations 

 as these, Dr, Barker concludes that axial illumination, in which a 

 large portion of the central rays of light are stopped off, is the only- 

 one which ought to be admitted in microscopic research — a conclusion 

 already arrived at by most of oui- best microscopists ; but all have 

 hitherto experienced a great difficidty in obtaining sufficient light, and 

 of economizing the oblique rays (those most valuable), which are 

 generally reflected to a large extent, and even dispersed at the under 

 siirface of the slide on which the object is placed. To obviate these 

 difficulties, Dr. Barker makes use of the immersion plan, by placing 

 between the slide and illuminator a film of water or oil ; this gets rid 

 of all, or almost all, the defects of former modes of illumination. 

 This film acts as a medium, permitting rays of light, without sensible 

 deviation or dispersion, to reach the object, and also allows all stage 

 movements to be freely used. The light obtained in the manner 

 indicated is almost piu'ely achromatic, and is sufficiently oblique to 

 give a black-gTound illumination with an eighth of an inch object-glass 

 (immersion), and will show clearly the dotted structure of the lines 

 on the Pleurosigma formosum with a quarter-inch object-glass, and with 

 a two-thirds used binocularly the surface and interior of certain 

 classes of objects are shown in a manner hitherto not seen. Dr. 

 Bai'ker's first experiments were with a flat-topped paraboloid, and, after 

 the meeting of the Academy broke up, the members had an opportu- 

 nity of viewing with it a specimen of the ConocJwlus volvox (a truly 

 beautiful object)." 



The ftuekett Club's Journal.— We are informed that the com- 

 mittee of the Quekett Club have re-considered their recent determina- 

 tion. It is now proposed to issue the ' Journal ' of the club as hereto- 

 fore. 



Dr. Woodward's Paper. — The figure omitted in the publication of 

 this paper will be supplied, printed on a separate " slip," in our next. 

 Eeaders will then have an opportunity of inserting it in the proj^er 

 place in their volumes. 



