JOUENAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



OCTOBER 1903. 



TEANSACTIONS OF THE SOCIETY. 



IX. — On the Rendering Visible of Ultra- Microscopic Particles 

 and of Ultra-Microscopic Bacteria, 



By H. Siedentopf, Ph.D. 



{Read June 17th, 1903.) 



The theoretical discussions concerning the capabilities of the 

 Microscope have, following the lines of Abbe and Helmholtz, in 

 the main related to the resolving power of objectives, having 

 established as a limit that structural elements up to a fineness of 

 a quarter fi (jj, = a thousandth of a millimetre) can be resolved. 

 Tins question of the resolution of structure is for most micro- 

 scopic research of material importance. It is the aim in micro- 

 scopy, not only to determine that there is a structure in an 

 object under investigation, but above all it is desirable to know 

 what that structure is like. Eesolution of structures more minute 

 than those indicated above has not been possible because the 

 light is diffracted by the elements of which the structure is 

 composed. 



But the question of the resolvability of a structure is not 

 the only one that can be applied to microscopic observations. 

 There may be cases in which we may have to be satisfied with the 

 simple evidence of the existence of a structure, just as in astro- 

 nomical research we do not confine ourselves to the observation of 

 the details of the planets, but also seek to render clearly visible 

 very faint, or ordinarily invisible, fixed stars. 



Now gold ruby glasses may be said to represent for microscopic 

 research that which the heavens with the fixed stars do for astro- 

 nomical investigations. These glasses appear perfectly clear and 

 homogeneous to the naked eye, and when tested by the usual 

 microscopic methods show no trace of turbidity. Gold ruby glass 

 is not the only object suitable for these investigations, but all 



Oct. 2Ut t 1903 2 p 



