Half-Yearly Compendium of Medical Science; A Synopsis of the American and Foreign Medicine, Surgery, and the Collateral Sciences Volume 21 (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: PHYSICS, BOTANY, CHEMISTRY AND TOXICOLOGY. I. PHYSICS. The Limits of the Optical Capacity of the Microscope. Dr. Lester Curtis, Chicago, sends the following communication upon this sub- k-d to the Chicago Medical Journal and Examiner, June, 1877: ? Two papers, one written by Professor Abbe, of Jena, aucl the other by the well- known Professor Helmholtz, on the limits beyond which, from the nature of light, it is impossible to carry the magnifying power of the microscope, with any profit, are it resent attracting considerable attention among those interested in the use of the instrument. It has been suggested to me that a condensed statement of the results arrived at by these investigators might be of interest to those readers of the Medical Journal and Examiner who might not have acccsS to the original papers. The first difficulty that stands in the way of a very great amplification of an object is the difficulty of obtaining sufficient illumination to render it clearly visible. The opening through which the object is viewed in a microscope diminishes just in rnportion to the magnifying power. The size of this apparent aperture has nothing to do with the size of any of the glasses of the microscope, and only varies with the changes in the magnifying power of the instrument; it makes 110 difference in what way this magnifying power is obtained, whether by the use of higher-power objectives, or higher eye-pieces, or by lengthening the tube of the instrument. The only circumstance that modifies the size of this orifice is what is called the angular- aperture of the objective, an objective of a small angle having a smaller field than an objective of a large angle. The size of this orifice can be seen by arranging the microscope as for an ordinary observation, and the...