PKOCEEDINGS OF THE SOCIETY. 245 



Messrs. Bausch and Lomb had sent this new model of their Conti- 

 nental Microscope for exhibition. It seemed to be a very substantial, 

 well made stand, with japanned horse-shoe base, and intended for use in 

 the laboratories. It had coarse rack adjustment and a fine adjustment 

 of the triangular bar form, with graduated head-screw. The stage was 

 square and plain and had a vulcanite top and the usual clips which 

 might with advantage be replaced by a simple sliding bar. 



The substage condenser was carried by a screw arm attached to the 

 side of the stage, by means of which the whole can be swung out. The 

 condenser was of the Abbe non-achromatic type, and had an iris diaphragm 

 below the back lens, and also one above the front lens. The latter can 

 only be useful when the condenser is removed and the mirror used 

 without a condenser, and then it should be racked down some little dis- 

 tance below the stage to be effective. 



Below the condenser there was also a ring carrying a stop for dark- 

 ground illumination, and a blue glass disk. 



Mr. Pillischer exhibited a very old Microscope which had recently 

 been sent to him for repair. It had a very peculiar form of stage 

 consisting of three oval plates, having rectangular apertures moving 

 excentrically on the fixed stage, and he thought the Fellows of the 

 Society might be interested in seeing it. He had not met with one 

 like it for thirty years. 



This stage was known as the " Tomes " stage. Mr. Charles Tomes 

 (afterwards Sir Charles Tomes, F.R.S., &c, Surgeon Dentist to the 

 Middlesex Hospital) was the inventor and for some years it was very 

 popular with medical men as an inexpensive and handy form of apparatus, 

 especially for dissecting purposes. As far as can be traced it was first 

 made about 1847, and remained popular for about ten years. This 

 Microscope belonged to the late Sir William White-Cooper, Ophthalmic 

 Surgeon to Her late Majesty the Queen, and has now been put in 

 working order for the use of his grandson. 



The President said they were to have that evening a very interesting 

 communication from Mr. J. W. Gordon on the Helmholtz theory of the 

 Microscope. He thought it was possible that, although many people 

 had some idea of who Helmholtz was, they might not know very much 

 as to what his life's work had been, and he had therefore prepared a 

 short account of this distinguished German philosopher, which he read 

 as follows : — 



Heemann Ludwig Feedinand von Helmholtz (1821-1894).* 



Originally a mathematician (by choice) he, by necessity, became a 

 surgeon in the Prussian army, and contributed important papers to 

 science from 1842 to 1894, the year of his death. Was Professor of 

 Physiology at Konigsberg from 1849 till 1855, when he removed to the 



* New vols. Encye. Britannica, xxix. (190 - J) pp. 247-8. 



