an instrument for measuring the Density of the Air. 83 



and that even with a less degree of sensibility it was requisite 

 to have the knife-edges sharper, straighter, or more nearly 

 parallel, and the agates more accurately flat; — these points 

 were accomplished by improved methods of preparing the 

 parts above named. 



The annexed figure is a side view of the essential parts of 

 the instrument. A is a hollow globe of glass of about 4£ 



inches diameter, hermetically sealed, having an eye in the 

 upper part where the tube from which it was blown has been 

 sealed : by this eye it is suspended by hooks from a steel stem 

 fixed to the brass frame B, holding an agate plate. This 

 agate plate rests on the knife-edge of the triangular prism of 

 steel as in the figure. C is another triangular prism of steel 

 fixed like the former to the brass lever of the balance. The 



G2 



