62 Proceedings of Learned Societies. 



ternal anatomy of insects was almost entirely neglected in this 

 country, and that the field was open to thousands of investigators, 

 each of whom could do good service to the cause of science. Speeches 

 were also made by Mr. Smith and Mr. Dunning, president and 

 secretary of the Society ; Dr. Gray, General Sir John Hearsey, who 

 has shown that devotion and service to science, is compatible with 

 the most active discharge of arduous military duties ; Dr. Wallace, 

 to whom we are indebted for the living specimens of the birds of 

 paradise, and several other gentlemen. 



ASTRONOMICAL SOCIETY. 



Mr. T. W. Burr exhibited and described a new eye-piece for tele- 

 scopes, which had recently been constructed for him by Messrs. 

 Horne and Thornthwaite of Newgate Street. It is an improvement 

 on the form of eye-piece much used in microscopes, and known as 

 the " Kellner," or " Orthoscopic," which consists of a double convex 

 lens for field-glass, and a meniscus for eye-glass. This combination 

 requires no stop, and gives a much larger field than a Huyghenian 

 eye-piece of the same power. The altei-ation made in the new form, 

 which has been named the " Aplanatic," consists in replacing the 

 meniscus by a plano-convex achromatic eye-glass, made up of a 

 double convex crown lens and a plano-concave flint one, similar to 

 one of the pairs of a microscope objective. This preserves the ad- 

 vantage of the large and flat field with better definition and freedom 

 from colour than the " Kellner," and is equally applicable to both 

 microscopes and telescopes. 



Mr. Burr stated that he had, during several months past, com- 

 pared an " aplanatic " eye-piece, giving a power on his telescope of 

 125, with a Huyghenian of 128, and found that upon the sun and 

 moon the field was one-third larger, taking in nearly, or sometimes 

 quite, the whole disc of those luminaries, while the increased light 

 rendered the eye-piece most valuable in observations of the planets, 

 nebulas, and double stars. 



In the discussion which ensued, Mr. Pritchard remarked that he 

 thought it unwise to depart from the Huyghenian form, which was 

 theoretically and practically perfect, but Mr. Burr replied that the 

 practical difference in definition and colour of the new form was so 

 slight that the increased field and light rendered the experiment 

 worthy of trial, and that all improvement would be stopped if we 

 refused to depart from an established construction. Mr. Carrington 

 also stated that he had found the "Kellner" eye-piece in constant 

 use in Germany, especially on comet seekers, where it was much 

 valued for its large field, and that he thought the proposed modifi- 

 cation now shown very likely to be an improvement, as nearly 

 effecting a perfect balancing of chromatic aberration. 



