23 



the pamphlet also being now in circulation. He begged permission, how- 

 ever, to offer a very few remarks on the subject. Prof. Abbe, to whom micro- 

 scopists owed so much, together with Dr. Schott and Dr. Zeiss, commenced 

 in 1881 a series of experiments in order to produce new kinds of glass, with 

 the result that objectives could now be manufactured in which the so-called 

 secondary spectrum was removed and the spherical aberration uniformly 

 corrected ; hence the application of the term apochromatic — a higher state 

 of achromatism than had been hitherto obtained. These objectives, when 

 used under the special conditions recommended, i.e., exact length of body 

 tube (ICO millimetres for the Continental and of 250mm. for the English), 

 and with their own proper 'eye-pieces, exhibit a marked improvement in 

 definition, and in other particulars, notably long working distance, increased 

 illumination, flatness of field, and a capacity for eye-piecing quite unusual in 

 lenses of the old construction. For the proper use of these objectives, and for 

 their more perfect correction, it has been found necessary to design new eye- 

 pieces called " Compensating Oculars." These were of two kinds — " Finder" 

 or " Searcher," and "Working." The first were of very low power ; in fact 

 No. 1 enabled an objective to be employed with its own magnifying power, 

 the same as if it were used as a magnifier without an eye-piece. The 

 working eye-pieces commenced with a power of four, anl gave good results, 

 even with the highest number.-. Ik' thought there was little doubt but that 

 the Finder or Searcher eye-pieces would supply a want long felt, as they 

 afforded sufficient field of view for general examination, and would be of 

 special service when immersion objectives were used, as the great inconve- 

 nience caused by having to change an objective, already adjusted, for one of 

 lower power, could now be avoided. They were also arranged upon a method 

 suggested by Professor Abbe, viz., on the increase in the total power of the 

 microscope obtained by means of the eye-pieces, as compared with that given 

 by the objective alone ; for example, on the microscope now showing A' 

 pellv.cida is the 3*0 mm. homo, immer. (|) objective, which of itself magnifies 

 83 diameters. The eye-piece employed is the No. 12, and magnifies 12 times. 

 Now, if 83 be multiplied by 12, the result is 996, or say 1,000 as stated by the 

 maker. There was another series called projection eye-pieces, which Mr. 

 Curties stated could not be shown on that occasion, but he hoped to bring 

 them to an early meeting and give a practical illustration of their value. 

 They were intended for purposes of demonstration on a screen or for photo- 

 micrography. He concluded by stating that upon the tables were arranged 

 microscopes of English, and of Continental form, each supplied with a full 

 series of the new objectives and eye-pieces, together with a number of fami- 

 liar objects, by which the members of the Club would be able to form an 

 opinion for themselves of these interesting and remarkable productions. 



Mr. J. E. Ingpen said he did not know that he could add anything to the 

 description given by Mr. Curties in his paper except of a technical nature, 

 and, therefore, not likely to be of general interest. But he might mention 

 that there was an editorial article in the April number of the Eoyal Micro- 

 scopical Society's Journal which, together with what appeared in the 



