252 [ftecess, 



from the under surface of which a drop of water is hanging. On a 

 support heneath, formed by three upright pins, place a small piece 

 of paper or thin glass, on the surface of which there is also a drop 

 of water. On depressing the disk till the two drops of water touch 

 each other, -the paper or plate will be instantly drawn up to it ; or if 

 the plate at the bottom be heavier than the disk, the latter will be 

 drawn down. 



Exp. 4. If a film of wetted collodion be partially stripped from a 

 glass plate, on being loosed it immediately flies back to its original 

 contact. The same effect may be observed if thin paper be wetted 

 and spread on a smooth sheet of glass, or be laid on the surface of 

 water. 



Exp. 5. Take two wine-glasses and dip their mouths into a strong 

 solution of albumen ; by a little dexterity two delicate convex films 

 will be obtained. On applying the most elevated points of the con- 

 vexities to each other, the films will be attracted and reduced to plane 

 surfaces strongly adherent to each other. The permanency of the 

 films enables the experiment to be repeated several times in suc- 

 cession. 



Exp. 6. When a soap-bubble is allowed to fall on an irregular 

 surface, such as a piece of lint or flannel, it maintains its spherical 

 shape ; but if a smooth surface, such as a sheet of glass, be brought 

 into sh'ght contact with it, the wall of the bubble will be immediately 

 attracted and flattened out upon it. In like manner, when two 

 bubbles come into contact by their convex surfaces and cohere, the 

 cohering surfaces become flattened ; and bubbles in a group cohere 

 by plane surfaces. 



Among other natural bodies, blood-corpuscles present certain pecu- 

 liarities of arrangement when withdrawn from their proper channels; 

 thus when a minute drop of mammalian blood is placed upon a glass 

 plate, the disks arrange themselves into rouleaux of well-known form. 

 They become attached to each other in this case by their biconcave 

 surfaces. They may also cohere by the edge or circumference, and 

 give rise to a tessellated appearance. This latter arrangement is most 

 easily obtained by placing a minute drop of blood on the under sur- 

 face of a thin piece of microscopic glass so as to be viewed through 

 it ; the blood being in a dependent position. A third mode of union 

 occurs when gum, gelatine, mucilage of linseed, or very thick solution 



