704 
PROCEEDINGS OF THE SOCIETY. 
improved model may have been, the original Microscope would now be 
of far greater value to us. 
Mr. Ingpen said he well remembered being taken by his father many 
years ago to the Society’s rooms in Sackville Street, and there, upon 
three brackets, were the Microscopes which Mr. Nelson had referred to. 
He also recollected the exchange being made of the lloss Microscope for 
one which was accepted by the Council of that time as being more useful 
to the Society for working purposes. The historical value of these 
things was greater than was generally supposed. 
Mr. J. Butterworth. read a paper c On a Pliotomicrographic Camera 
designed chiefly to facilitate the study of opaque objects,’ exhibiting 
upon the screen a diagram of the apparatus referred to, and a series of 
photographs of opaque mineral sections. Specimens in further illustra- 
tion of the subject were also exhibitedrunder the Microscope. In answer 
to inquiries from Fellows of the Society, it was explained that the light 
used was that of an incandescent gas-burner. This was reflected from a 
concave mirror to another concave mirror in front of the object, and 
thence upon the object itself, which was fixed upon the stage of a Micro- 
scope having the tube in a horizontal position ; the photograph being 
taken by a camera in the usual way. Greater distinctness of differentia- 
tion was obtained by acting upon the polished surface of the object by 
hydrochloric acid. In this way photographs taken at successive stages 
of grinding down were made to furnish views equivalent to a series of 
sections, which were of great value in determining structure. 
Mr. Nelson thought they ought to express their admiration of these 
photographs, which were certainly the best he had seen of opaque sec- 
tions. The subject had always been regarded as a very difficult one, 
but the method described to them that evening went far towards over- 
coming the difficulties. 
Mr. George Murray said the great trouble in satisfactorily examining 
these substances was the impossibility of cutting thin successive sec- 
tions ; but the method which had been explained to them that evening 
enabled students by the aid of photography to produce results equivalent 
to such sections, and to place this key to their study within their grasp. 
He thought it was possible to predict that great good might come from 
this new method of research. 
The thanks of the Society were, upon the motion of the Chairman, 
cordially voted to Mr. Butterworth for his paper and the interesting ex- 
hibition he had given. 
Mr. T. Comber read his paper * On the Occurrence of Endocysts in 
the Genus Thalassiosira .’ The subject was illustrated by photomicro- 
graphs shown upon the screen. 
Mr. George Murray detailed some observations made in connection 
with the subject in the month of March, which had enabled him to de- 
termine how these endocysts arose. In illustration of the subject he 
exhibited some photographs upon the screen showing Coscinodiscus which 
