7 
physical properties j the freshly cut surface has a bluish white lustre, which 
rapidly tarnishes on exposure to the air. It undergoes gradual oxidation and 
is best preserved in water. It occurs in many specimens of iron pyrites, often 
taking the place of arsenic, a common impurity of this substance. The salts 
of Thallium having lately been noticed as possessiag very brilliant polarizing 
properties, Mr. Martin felt induced to procure a series, and mount them as 
objects for the microscope ; and he presented a set of a dozen slides for the 
Society's Cabinet. The Bitartrate, Oxalate and Sulphate, produce the most 
pleasing effects, but all give more or less colour. A vote of thanks was 
accorded to Mr. Martin for his donation. 
The Hon, Secretary placed on the table a gathering from the Bristol 
Float which afforded many interesting objects for the inspection of the 
members present. Amongst other forms were noticed Brachionus urciolaris, 
Rotifer vulgaris, Actinurus neptunius, Stentor roeselii, Vorticelea convallaria, 
Actinophrys sol, Bacillarioe, &c, &c, &c. 
