1891.] MICROSCOPICAL JOUKNAL. 279 



Mr. Frank Crisp, of London, ha*, one of the largest and niobt com- 

 plete collections of this character. 



Dnring- the last fifteen years great progress has been made in the im- 

 provement of the objectives or object glasses. The English, Ger- 

 mans, and Americans have been in active competition, and each year 

 has witnessed some great a<lvance by one or the other in the perfecting 

 ot objectives. Ten years ago the President of the American Society 

 of Microscopists in his annual address remarked, '• that lenses which 

 were believed to have so nearly reached the limit of perfection fifteen 

 years ago are antiquated now, and the theoretical limit of perfection 

 has moved forward like the horizon, and is as far off as ever." Com- 

 pare the state of the microscope of 1S82 with 1891, and note the 

 change that has been realized. In 1869, in a letter addressed to Col. 

 Woodward, U. S. A., Nobert expressed his belief that it was physi- 

 cally impossible to resolve with a 1-16 lens more that 91,000 lines to 

 the inch. But a short time after Col. Woodward had succeeded with 

 a Powell & Leland lens, 1-16, in resolving 112,000 lines to the inch — 

 21,000 lines more. The highest record of resolution that has been at- 

 tained is that of Mr. Fassoldt, who has ruled and demonstrated 120,000 

 to the inch. This may be considered the present limit of visibility. 

 The theoretical limit of 1869 was passed. 



Water immersion lenses proved a gain over the former dry lenses. 

 Later, the latter gave way to the homogeneous immersion lenses. But 

 a few years since, 1S86, the labors of Professor Abbe brought forth a 

 new kind of optical glass, the invention of which gave new life to mi- 

 croscopy. These special lenses, called apochromatic, are remarkable 

 for their freedom from spherical aberration, practically colorless, giving 

 an image clearer and of better definition than could be gained by the 

 achromatic lens. Of special advantage are the new glasses in photo- 

 micrography — the faithful recorder of all microscopic observations. 



In this brief description of the history of this wonderful instrument 

 mention has been made of but a few facts concerned in its develop- 

 ment. If you will look into some of the old works of the i6th and 

 17th centuries, where much of the interesting history of the micro- 

 scope is written, you will be curious to observe how, from the exciting 

 curiosity it was in its infancy, it grew to the valuable, remarkable, and 

 perfect instrument of research it is to-day. 



Look deeper and see the investigations and discoveries that have fol- 

 lowed its birth. Fields of investigation unheard of were opened up. 

 VV^hat of the branches of science, histology, biology, embrvology, bac- 

 teriology.' What have we learned from this instrument, which a few 

 hundred years ago was a toy, delighting and bewildering alike flie 

 makers and the curious employers.' 



Mr. Wilson remarks : " What the future development of the micro- 

 scope may be it is impossible to say. Fifty years ago no one would 

 have dreamt of the great advances which have been made up to the 

 present time, and only a few years ago the limit to the further improve- 

 ment seemed to have been reached when the introduction of the new 

 kind of glass gave a fresh impetus to microscopy." 



"'There remains, of course," says Professor Abbe, " the consolation 

 that there is much between heaven and earth that is not dreamt of in our 

 philosophy. 



