1078 SUMMARY OF CURRENT RESEARCHES RELATING TO 



together, and the slide prepared as above — refractive index about 2 • 3. 

 Also selenium by itself — refractive index 2 ' 6. 



With all the above media A. pellucida was splendidly resolved. 

 These experiments by Dr. Morris were undertaken with a view of 

 enabling objectives of the older constructions and of less angular 

 aperture to resolve the highest test diatoms as easily as the new wide- 

 angled homogeneous lenses." 



" Mr. Hirst exhibited A. pellucida resolved by Zeiss's 1/8 water- 

 immersion objective, in a manner scarcely to be surpassed by the new 

 oil-immersion objectives. The diatom was mounted in sulphur — this 

 proving Dr. Morris's theory that a highly refractive mounting medium 

 enables low-angled objectives to compete in resolution with the new 

 oil-immersions." 



We do not quite understand how such a notion could bave arisen, 

 unless it was from misapplying a little the principle which requires 

 the use of a mounting medium of at least equal refractive index to 

 the aperture of the objective, in order to fully utilize such aperture. 

 It need hardly be pointed out here that if an objective has an aper- 

 ture of say • 75 only, nothing that can be done with the mounting 

 medium can possibly increase the aperture or resolving power of the 

 objective. The advantages of highly refracting media are limited (as 

 shown by Mr. Stephenson in his original paper *) to intensifying the 

 images. An appropriate medium will enable the full effect of a given 

 aperture to be utilized, but cannot increase it or make an objective 

 of low aperture " resolve the highest test diatoms as easily as a wide- 

 angled homogeneous lens." We propose to return to this subject 

 when we can find space for a few diagrams, which will, we hope, 

 prevent such an idea as that above quoted being again put forward. 



American Society of Microscopists. — [Conclusion of Report of Cleveland Meeting. 

 Also a serio-comic account of the working of the Session and Soiree, from the 

 ' Plain Dealer,' containing such comments as the following : " Having looked 

 at the wriggling worms [in printers' paste] that made the mass literally alive, 

 they could understand why it is that newspaper paste so seldom sticks. The 

 insects literally walk off with the pasted clipping on their backs."] 



Amer. Mon. Micr. Journ., VI. (1885) pp. 195-9. 

 See also Queen's Micr. Bull, II. (1885) pp. 33, 34-5. 

 Banks, C. W. — [Electricity under the Microscope.] 



[Exhibition of " Stokes's Spark Apparatus," and "Moore's Geissler tube." 

 " Mr. Banks also showed the peculiar effects produced by the passage of 

 the electric spark through various substances — such as oil, filings of 

 metals, films of soot, finely powdered plumbago, &c. These displays 

 were in nearly every case vivid and beautiful. TlJe oil imparted an in- 

 tensely green colour to the spark ; while the course of the latter through 

 the filings of metals produced entirely different, though not less striking 

 effects. A peculiar appearance was produced by the passage of the calo- 

 rific spark through a mixture of small globules of mercury and gold- 

 filings. The current was thereby interrupted in such a manner that 

 instead of continuous streams of light, these were broken up iato dots, 

 and dashes, very strikingly resembling a luminous Morse alphabet. The 

 entire exhibition was attractive by reason of its novelty as well as its 

 beauty."] 



Proc. San Francisco Micr. Soc, 1885, Sept. 23rd. 



* See this Journal, ii. (1882) p. 163. 



