267 



PROCEEDINGS OF THE SOCIETY. 



MEETING 



Held on the 15th of February, 1905, at 20 Hanover Square, W. 

 D. H. Scott, Esq., F.R.S., etc., President, in the Chair. 



The Minutes of the Meeting of the 18th of January, 1905, were 

 read and confirmed, and were signed by the President. 



Mr. Finlayson's paper describing his Comparascope was read bv 

 Dr. Hebb. 



The President said he understood that the instrument described in 

 this paper was on the table for inspection. He had seen photographs 

 of it, and also a photograph taken by it, and thought it was clear 

 that there was a use for an instrument of this kind. He had often 

 wanted something of this kind in the course of his work on the structure 

 of fossil plants, as the only means available for comparing objects was 

 by photographs, which did not always show all the detail, so that an 

 invention which enabled two objects to be seen together in the same 

 field of view would be of very great advantage. 



Dr. Hebb said that another method of making comparisons between 

 two objects was described in the Society's Journal for February, by 

 which specimens were mounted one over the other on the same slide, so 

 that by focussing up or down either could be brought into focus, and a 

 comparison could be easily made between the normal and abnormal. 



Mr. A. D. Michael said that in the case of very small objects, having 

 both in the field at once, without any separate focussing being required, 

 would be a distinct advantage if they were sufficiently in the centre of 

 the field to secure good definition ; but where the objects were larger 

 they could not be got into the same field except with a low power, which 

 might not show the details sufficiently. For small objects, however, he 

 thought the arrangement described would answer admirably. 



Dr. Hebb said that they had received a photograph of Pl&urosigma 

 angulatum, taken by Mr. Merlin, and sent to the Society by Mr. Nelson, 

 who thought it one of great excellence. 



The photograph was exhibited, and the following description by 

 Mr. Merlin of the method by which it was taken was read by Dr. Hebb : 

 P. angulatum. Fractured Valve X 7500. Photographed with Zeiss 

 apochromatic £-in. N.A. 1 -425, and a Powell X 40 compensating ocular. 

 The valve is partly in " pearl dot " and partly in " black dot " focus. 

 Postage stamp fracture and optical intercostals well shown. Axial illu- 

 mination, with full aperture of Powell's dry apochromatic condenser. 

 The sun's image from a heliostat being sharply focussed on to the valve. 

 No auxiliary condenser employed. Valve mounted in realgar. Deep 

 violet screen. Direct photo taken on an Eastman kodoid film. Expo- 

 sure, 1 minute. 



The thanks of the Society were unanimously voted to the authors of 

 these papers, and to Dr. Hebb for reading them. 



