272 Scientific Intelligence. 
by the atmosphere, the alteration which change of atmospheric pressure 
renders atin in the counterpoise, indicates the change of pressure — 
which has oc : 
Several sireitietanses require attention, besides delicacy in the balance 
and accuracy in the weights, to secure accuracy in the results. Ist. The — 
tube must be of uniform capacity pi a its length, excepting so 
ng capacity in the different — 
pe es to a sisi sane, say, to sey shin’ pe 
= bas at GS senpersiant of 32° Fahr. If now a tube has been used having 
city of 1000 grs. of mercury at 32° F. for an inch - its length, : 
‘ would have a diameter of about °6 of an inch, each grain will . 
represent, the thousandth part of an inch; and if a correction has beet — 
made es the capillarity of the tube, all its indications, at whatever tem- 
ill represent the height of the ae 8 at 32° F., and require 
correction only for the altered — of the tu bee. 
instrument has been ere indicated. 
