A SIMPLIFIED BAROMETER Many teachers of chemistry, and physics as well, have found that elementary students not only need help in reading an ordinary barometer but also frequently fail to understand the simple principle involved. Some eighteen months ago four of the barometers, as herein described, were placed in service in our elementary chemical laboratory, in addition to several others used in our research laboratories. These barometers were constructed in our own shops. A description follows: The base board has a wide slot milled out to accommodate an ordinary meter stick so that the two surfaces are flush. The slot is given sufficient clearance to allow the meter stick to slide freely. .A friction spring a is provided to hdid the meter stick in any position. An ordinary barometer tube without scale is used. The lower end of the meter stick is provided with a double pointer b, one behind and one in front of the barom-' eter tube. The lower edges of these pointers, of course, correspond to the lower (zero end) of the meter stick. By means of a handle c the meter stick is moved until the upper surface of the mercury exactly coincides with the ldwer edges of the pointers. The sleeve d is1then set until its pointer coincides with the upper surface of the mercury column. The height of the mercury column is then directly read off on the meter stick. Corrosion of the exposed mercury column has been materially lessened by means of a tube e filled with fine copper turnings. During the eighteen months that the four barometers referred to have been in use some two thousand students have each in turn read them several times. A simple set of directions mounted beside each barometer has provided ample guidance to the students using them. Furthermore, the underlying principle involved has been grasped.
