PROCEEDINGS OF THE SOCIETY. 447 



referred to the complete paper as being one of the most valuable 

 and useful papers that had ever been brought before the Society, 

 dealing as it did not only with the theoretical part of the subject but 

 establishing also a rational standard for the practical construction of 

 objectives. 



The Chairman considered that Professor Abbe's paper was indeed 

 a most useful one, and that it would be greatly appreciated by practical 

 opticians. 



Mr. Beck said that he considered it was an exceedingly valuable 

 paper, and one that would enlighten a great many persons as to the 

 relative value of aperture and magnifying power in regard to which 

 great confusion had existed. There were people who thought that if 

 they could get a 1-inch objective with an aperture of 120', they could 

 resolve difficult diatom tests. He had heard it claimed that such 

 glasses had been made, but although he had ordered one he had not 

 yet been able to get it, and hopes that might have been raised by 

 these announcements would be damped by the contents of Professor 

 Abbe's paper. He was very glad that it had been written, because it 

 had been his impression for some time that Professor Abbe had been 

 working exclusively in the direction of wide apertures. 



Mr. Ingpen was surprised to hear Professor Abbe, of all persons, 

 charged with an exclusive approval of large apertures, for if any one 

 looked at Zeiss's catalogue, they would see at once that all the dry 

 lenses were of remarkably small angles, nothing exceeding 110°. 



Mr. Crisp said that the most opposite notions had been held as to 

 Professor Abbe's views on wide or narrow apertures. Some years 

 ago it was stated, at one of the Society's meetings, that he advocated 

 only narrow apertures, and some correspondence took place in regard 

 to it in the ' Monthly Microscopical Journal.' Again, later, it was 

 insisted that Professor Abbe considered all but wide powers useless 

 to the microscopist ! The fact was that Professor Abbe had, since 

 the date of his earliest observations on aperture, advocated the main- 

 tenance of a proper ratio between aperture and power — wide apertures 

 for high powers, and small apertures for low powers — and had 

 always insisted on the great importance of perfecting the construction 

 of moderate apertures. The confusion had arisen from the fact of 

 Professor Abbe having shown, in connection with his theory of micro- 

 scopical vision, that wide apertures, and wide apertures only, gave 

 true images of minute objects ; but it did not, of course, follow from 

 that, that wide apertures were to be universally usedj with low powers 

 and with objects unsuitable, either from their rec[uiring depth of 

 vision or for other reasons. 



Mr. J. Mayall, jun., exhibited Ross's "Hospital Microscope," 

 the speciality of which is the fine adjustment, which is of simple 

 construction. 



Dr. Maddox read a pai^er " On Some Micro-organisms from Ice- 

 Water and Hail," illustrated by a number of photo-micrographs. 



The Chairman inquired how Dr. Maddox accounted for the exist- 



