153 



the whole inferior to tbe Iluyghenian. There was another well-known " Kellner " 

 eyepiece, with a meniscus achromatic eye lens and a double convex single field 

 lens. The field was very large and flat and the definition fine, particularly for 

 surface markings, but Mr Ingpen thought the great size of the field distressing 

 to the eye. By using a diaphragm making a square or oblong field of view, this 

 eyepiece became very useful in searching over crowded slides, as objects were 

 often missed in the overlapping of circular fields. There was an excellent modi- 

 fication of this eyepiece by Home and Thorntbwaite, called by them the ap- 

 lanatic eyepiece. There was another form constructed by Dr. Steinheil, in which 

 the eye lens was double, consisting of two piano convex lenses with their convex 

 surfaces towards each other. Various positive eyepieces were then described — 

 the earliest, Eamsden's, still used for micrometers, the Eev. J. B. Eeade's ach- 

 romatic solid eyepiece, Browning's achromatic for reflecting telescopes, and 

 others. Most of the eyepieces described were exhibited and their construction 

 shewn by diagrams on the black board. Mr. Ingpen concluded by referring to 

 the recent suggestion of Dr. Steinheil to use long bodies and low powered eye- 

 pieces (shewing an eyepiece suitable for that purpose), and by calling the atten- 

 tion of the members to the desirability of testing their eyej)ieces as well as their 

 objectives. 



The President proposed a cordial vote of thanks to Mr. Ingpen for his valuable 

 communication. Carried unanimously, 



Mr. Burr said that he believed he was the originator as well as the first pos- 

 sessor of the aplanatic eyepiece made by Home and Thornthwaite. Having used 

 a Kellner eyepiece for the microscope, he thought it would be very desirable to 

 get one of similar construction made for his telescope, and having talked it over 

 with Mr. Hislop and Mr. Ackland, the aplanatic eyepiece was the result, and he 

 found its performance to be very satisfactory, as it took in a much larger field 

 than usual without kss of light. The eyepiece was mentioned very favourably 

 in the monthly notices of the Royal Astronomical Society, and it gave great satis- 

 faction, not only to himself, but also to the present possessor of the instrnmeut. 

 With respect to the Eamsden eyepiece, he had the opportunity of knowing that 

 the late Mr. Thos. Eoss thought highly of it and fully intended to have done 

 something towards making it achromatic. 



Mr. Ingpen said that Mr. Browning made a positive eyepiece which he believed 

 worked well. He had omitted to mention the Barlow lens in the course of his 

 former observations ; it was, he thought, practically the same as Tolles' Am- 

 plifyer. Dr. Pigott said he had used and discarded it, but whether he gave it a 

 fair trial before he took to his aplanatic searcher, he could not say. The ap- 

 lanatic searcher no doubt arose from what was stated in the paper of Mr. Lister. 



Mr. Burr observed that he had a Barlow lens made to his telescope, because 

 he complained that he did not get the mici'ometer sufiiciently magnified. 



Mr. Ingpen said that the great Newall Telescope was found to be not achro- 

 matic, and that the defect of the object glass had been corrected by the use of a 

 Barlow lens. 



The Secretary read a letter from the Hackney Scientific Society to those mem- 

 bers of the Club who recently rendered valuable aid as exhibitors of objects at 

 the soiree of that society. 



The proceedings then terminated with a conversazione at which the following 

 objects were exhibited : — 



Tibia of Ovis Aries (transverse and Ion- ") i ti r n n • , 



gitudinal sections 5 ^^ ^^^- ^- Daintrey. 



Isthmia enervis *' Mr. R. T. Lewis. 



