AN INTERESTING PSEUDOSOLID 



291 



deterioration taking place. It also proved possible to strain 

 these prisms to fracture and to lay them aside to dry, which 

 they do with but little change of form, and to study or photo- 

 graph these fractures at leisure. Many of these specimens 

 resembled fractured close-grained rock so closely in the photo- 

 graph as to be practically indistinguishable from it. 



The apparatus with which the measurements upon these 

 prisms were made was of extraordinary sensitiveness and 

 admitted of very rapid manipulation. 



A fine analytical balance was mounted with a mirror at the 

 top of, and at right angles to, the beam, which could be 

 observed with a telescope and vertical scale at a considerable 

 distance, thereby furnishing a very sensitive measure of the 



Fig. I. 



motion of the beam. A die was then prepared with which 

 cylinders of uniform size could be cut out of a mass of foam 

 and deposited quickly upon one of the pans of the balance. 

 The w^eight of the cylinder was compensated by an equal 

 weight in the other pan. A glass bridge was then fixed in posi- 

 tion over the foam cylinder and the pan raised until the upper 

 surface of foam was in perfect contact with the glass bridge. 

 The illustration (Text-fig. i) will serve to show the distribufion 

 of the essential parts of the apparatus. 



Having placed our cylinder in position between 2 clean glass 



