Kater on the Construction of a Balance. 41 



pins are to be brought into lateral contact with the scale pans 

 by means of the ends k, I, when the beam is elevated above its 



support. The knife edge being then lowered upon the agate 

 planes, and the pins withdrawn, any want of equilibrium be- 

 comes instantly perceptible. 



I am, dear Sir, 



Yours very faithfully, 



Henry Kater. 

 W. T. Brande, Esq. 



Art. VI. On Pilchstone. J5y J. Mac Culloch, M.D. 

 F.R.S., <?fc. 



The information to be procured respecting this rock is so 

 scanty, from its limited occurrence and the imperfection of the 

 observations hitherto recorded, that I cannot pretend to place 

 its geological history in a very luminous point of view. There 

 is reason to suspect that some of the remarks on its position 

 have been warped by theoretic views of the same nature as those 

 which have influenced the corresponding observations on tlic 

 trap rocks ; while it is also apparent, that the peculiar jaspers 



