JOURNAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



AUGUST 1903. 



TRANSACTIONS OF THE SOCIETY. 



VI. — Tlic Helmholtz Theory of the Microscope. 



See Pogg. Ann., 1874, Jubelband, p. 569. Helmholtz' Wissenschaftliche Abhand- 

 lungen, vol. ii. p. 185. Proceedings of the Bristol Naturalists' Society, N.S. vol. i. 

 part 3. Monthly Microscopical Journal, N.S. vol. xvi. p. 15. See also Appendix, 

 Note iv. 



By J. W. Gordon. 



(Read March 18th, 1903.) 

 Plate VI. 



Helmholtz' paper bears the title, ' The Theoretical Limits of 

 Eesolving Power in. the Microscope,' and is directed to the formal 

 conclusion that a certain denned magnitude forms the necessary 

 and impassable limit of resolving power in the Microscope or in any 

 other optical instrument. But it will, I think, be found that the 

 merit of the paper lies not in this formal result, which is, in fact, 

 not successfully established, but in the line of investigation which 

 Helmholtz here strikes out, and without following it to its practical 

 issues, pursues far enough to present his readers with a surfeit of 

 interesting and valuable suggestions. These suggestions are, many 

 of them, so obscure and conveyed by such subtle hints that they 

 may well escape attention, and apparently they have escaped 

 attention to the present time. It will be my endeavour this 

 evening to bring the Helmholtz method of investigation to your 

 notice, and to divest it of its somewhat repulsive mathematical 

 garb in order that it may be rendered by translation into physical 

 terms more presentable in general society. I shall also ask leave 

 to apply the results of this investigation to certain practical 

 matters connected with the construction and use of the Microscope, 

 Aug. 19th, 1903 2 o 



