489 



tube-length would require consideration, as there are plenty of 

 good objectives not provided with collar correction. He would 

 suggest a simplification of the lecturer's method — namely, camera 

 extension squared, divided by diameter of Ramsden circle squared, 

 multiplied by a constant found by experiment. He assumed 

 that objective.- were all of the same transparency, and that lamp- 

 distance and condensers, etc., remained the same. 



Mr. B. J. Capell inquired as to the possible necessity of a 

 factor taking into consideration the mounting medium — dis- 

 criminating between, say, realgar and monobromide ; and with 

 respect to the use of isochromatic plates, he thought them very 

 useful, but suggested that at times the selective power of the 

 ordinary plate would be equal to the use of a blue screen. 



In replying. Dr. Reid thought the subject would cause more 

 variation than the medium. A knowledge of isochromatic photo- 

 graphy was very useful, and, in fact, necessary, in photomicro- 

 graphv. He found that with an oil-lamp better contrast was 

 obtained with isochromatic than with ordinary plates. It was 

 sometimes necessary to use red-sensitive plates, and sometimes 

 ordinary plates. It depended on the subject. Referring to Mr. 

 Stokes's remarks re N.A., he would have to measure distance 

 between eyepiece and ground-glass every time, but by the 

 lecturer's method would only have to refer to tables. 



At the meeting of the Club held on March 5th, 1909, Dr. 

 E. J. Spitta, F.R.A.S., F.R.M.S., Vice-President, in the Chair, 

 the minutes of the meeting held on February 5th were read 

 and confirmed. 



Messrs. H. G. Troughton, R. Beer, and 0. Collier were balloted 

 for and duly elected members of the Club. 



Mr. Lees dirties, jun., for Messrs. C. Baker, exhibited and de- 

 scribed three new models of microscope stands just brought out by 

 his firm. This new form of their well-known D. P. II. model is 

 provided with a body-tube 1| in. in diameter, with draw-tube carry- 

 ing an eyepiece 2 3' 2 mm. in diameter. It is fitted with diagonal 

 rack, coarse adjustment, and is carried on a limb cast in one piece, 

 with opening to receive the fingers when lifting. The fine-adjust- 

 ment milled heads work at the sides of the limb, and actuate 



