ON THE WATER IN THE CHALK. 14-7 



many points in the ultimate tissues, both of animals and vege- 

 tables, that the oxy-hydrogen microscope will fail to display, and 

 for which no substitute for the direct eye of the observer can be 

 provided. 



POSTSCRIPT. 



At a subsequent meeting of the Society, held at his own house, 

 Mr. Pumphrey conducted a series of experimental demonstrations, 

 showing the advantages to be derived from the exhibition on the 

 screen of magnified images of actual objects, and also pointing 

 out the difficulties attending the process, and where it was most 

 likely to fail. Carefully-prepared micro-photographs were dis- 

 played on the screen, along with magnified images taken direct 

 from the same objects ; and the opinions advanced in Mr. 

 Pumphrey's paper were endorsed by all present — namely, that 

 when the object was to demonstrate to a class, or to a small com- 

 pany, who can critically examine the image as displayed on the 

 screen, the image, as taken direct from the object, was much to be 

 preferred ; but that for large companies, and where the close 

 examination of the image would be impracticable, the micro-pho- 

 tograph was better adapted to the purpose. The subject was also 

 considered with reference to the attainment of the same end by 

 means of carefully-prepared diagrams and black-board illustrations. 

 It was felt that unless there was a probability of the former being 

 frequently used, the requisite expenditure of time and labour was 

 too great for most persons ; but as regards the latter the opinion 

 was expressed that the free use of the blackboard, in illustration of 

 the papers read to the Society, was a great advantage. 



®n tbe Mater in tbc Cbalk beneatb tbc 

 Xonbon Cla^ in tbe Xonboii Basin/' 



By Robert B. Hayward, M.A., F.R.S. 



MY object in the present paper is not to bring forward any 

 new facts or observations, but the collocation and juxta- 



* Read at a meeting of the County of Middlesex Natuial History Society. 



