646 PROCEEDINGS OF THE SOCIETY. 



From 



Slack, H. J., F.G.S., &c.— Marvels of Pond Life. 3rd edition. 



158 pp., 7 plates and 50 woodcuts. 8vo. London, 1878. Mr. CrinjJ. 



Van Heurck, H. — Le IMicroscope: sa Construction, son Manie- 

 ment, et son Apjilication a 1' Anatomic ve'ge'tale et aux 

 Diatomees. 3rd edition. 346 pp., 12 plates and 170 wood- 

 cuts. 8vo. Bruxelles, 1879 The Author. 



Woodward's Prism. (Described in ' Journ. Roy. Micr. Soc," 



i. (1878) p. 246.) Mr. Crisp. 



Young's Campliine Lamp Cotton, for distribution among the 



Fellows Mr.W.T.Suffol':. 



Zittel, K. A. — Beitrage zur Systematik der fossileu Spongien. 



132 pp., 10 plates. 8vo. Stuttgart, 1879 Mr. Crisp. 



The President said he had much pleasure in announcing that they 

 were favoured that evening by the presence of a distinguished Honorary 

 Fellow of the Society — Professor Abbe, of Jena — who would read a 

 paper " On a New Method of Correcting Spherical Aberration." 



Professor Abbe on rising was very warmly received by the meeting, 

 and proceeded to explain the method which he had adopted for cor- 

 recting spherical aberration, illustrating his remarks by diagrams on 

 the black-board as he proceeded. He also exhibited an objective in its 

 complete form made upon the new principle. 



The President, in moving a vote of thanks to Professor Abbe for 

 his communication, felt sure that the meeting must have been highly 

 gratified by his very clear explanation of a difiScult subject. 



Mr. Wenham said it appeared to him that Professor Abbe had 

 mooted a very important question in reference to the difference between 

 the magnifying power of the centre and the margin of the field, which 

 had not yet been properly investigated. He wished to ask Professor 

 Abbe whether he found that this distortion bore any regular ratio to 

 the angle of aperture ? 



Professor Abbe said that the difference of amplification was not the 

 same as distortion. It was a difference of amplification which might 

 arise in the centre of the field of view from difference of conjugate 

 points. It was quite distinct from the distortion due to different 

 amplification in different parts of the field. 



Mr. Palmer inquired what particular form of front lens was 

 employed. 



Professor Abbe said he had brought one with him to show the 

 construction. It was a lens about 5^ greater than a hemisphere, and 

 was mounted on a very thin plane plate of glass, of somewhat greater 

 diameter than the plane face of the lens, the projecting zone serving 

 for the mounting in the metal cell. This the Professor exhibited, 

 also giving a diagram showing the posterior lenses in the combination, 

 and explaining wherein the new arrangement differed from previous 

 combinations. Very great difiiculty had been met with in producing 

 accurate figure to the edge of this new front lens ; he could, however, 

 vouch for the fact that excellent figure had been obtained up to 5° or 

 10'^ beyond the hemisphere. 



Mr. Beck thought they must all feel very much indebted to 

 Professor Abbe for bringing this subject before them, but he wished 

 to inquire whether the plan which he had suggested for doubling up 



