772 SUMMA.RY OF CURRENT RESEARCHES RELATING TO 



minute structure near the present limits of vision from the images it 

 gives. At present we can scarcely say more than that a single series 

 of lines will never appear as anything else but lines under an objective 

 of sufficient aperture and with proper amj)lification, though they may 

 appear doubled or quadrupled in number and fineness. They will not 

 apjjear more widely spaced than in reality, and will not take on the 

 semblance of dots or hexagons. But dots may appear as lines of vary- 

 ing fineness, or in varying direction, or as dots or bodies of various 

 shapes and sizes, according to the manipulation used, and we are as 

 yet without any sure way of judging of their real nature from their 

 microscopic image. But that these structures can yet be verified and 

 their true nature ascertained I confidently believe, even though Abbe 

 himself has been unable as yet to solve the puzzle, and the inquiry 

 may be long and difficult. Whether the Microscope can ever reveal 

 the existence of any structural detail finer than that which now seems 

 to mark the limit of vision, is another question. Doubtless with 

 other materials than our present crown and flint glass, and with still 

 fuller imderstanding of the principles involved, objectives transcending 

 the present limits may yet be made and new difficulties of resolution 

 appear. But at present we are not ready for such machines. We 

 have not learned to use correctly what we have. The finer structures 

 now revealed as at present are not understood by us. When we have 

 learned how to verify what we now can see we will be ready for 

 further gifts, for more powerful lenses from our opticians, — objectives 

 of wider aperture, immersed in fluids of refractive index equal to 

 their own — and when we are ready for them they will doubtless be 

 produced. At the present time the Abbe difii-action plate offers itself 

 as a most fruitful field of study, and when we can learn to discrimi- 

 nate without hesitation the various appearances of its squares and 

 rhomboids we can attack anew the mysteries of histology, resolve the 

 diatom frustules in a truer and more perfect sense, investigate the 

 bioplasm theory to a final and satisfactory conclusion, and perhaps 

 discriminate optically between the septic and the pathogenic bacteria, 

 learn the true structure of muscle and the real meaning of its stria- 

 tions, and in a thousand other ways approach a little nearer to an 

 understanding of the mystery of life and the wonderful, beautiful 

 symmetry of the structure of the universe of God." 



Examination of the Corpuscles held in Suspension in Water.* — 

 Amongst the essential characters of the potability of water, limpidity, 

 E. Marchand says, ought to be imperiously exacted. The perfect 

 transparency of the liquid can generally be sufficiently ascertained by 

 simple examination, but a more accurate observation can be made by 

 passing a ray of sunlight through the water inclosed in a glass flask 

 surrounded by black paper, in which are two opposite rectangular 

 apertures, through one of which the ray passes while the observer 

 looks through the other. When the liquid is optically pure the light 

 traverses it without obstacle, but however few particles there may be 

 held in suspension, each of these, on being illuminated, is visible 



* Comptes Keadus, xcvii. (1883) pp. 49-50. 



