3 I2 



The barometer must be mounted either in the office or the 

 observer's private quarters. A spot should be selected free from 

 draughts and other disturbing influences (such as fires, etc.), and with 

 a good side light if possible. In mounting it, first fix the detached 

 bracket on the wall at a height of four feet above the floor, and then, 

 taking the barometer very carefully out of the box, drop the end of 

 the " arm " into the bracket. If the wall be constructed of stone or 

 brick, a wooden plug should be inserted, and the bracket affixed 

 thereto. Paste a piece of white paper on the wall immediately 

 behind the top part of the tube. 



The thermometers are : Dry bulb, wet bulb, maximum, and 

 minimum. These are all placed in the Stevenson screen. The two 

 former are to be hung vertically in the brass clips attached to the 

 moveable wooden arms at the back of the screen. The maximum 

 and minimum are to be laid horizontally in the wooden brackets 

 attached to the uprights in the front part of the screen, the bulb ends 

 being to the left and slightly lower than the other ends. 



The rain guage must be in a well exposed situation. Its rim 

 must be level and about a foot above the ground. 



Reading the barometer. There are two scales, one fixed and 

 one movable. The latter is called the " vernier." First turn the 

 " vernier " up until the light can be seen between the top of the 

 mercury and the bottom of the vernier. Then turn the vernier 

 down slowly until its bottom edge just touches the rounded top of 

 the mercury. In doing this it is absolutely necessary that the eye 

 should be in a line with the front and back edges of the vernier, and 

 the observer must move his head up and down so as to be quite sure 

 of this. The barometer, being now set, is read as follows: First 

 write down the reading of the fixed scale next below the point where 

 it is cut by the bottom of the vernier. The divisions of the fixed 

 scale are as follows : 



30.200 



30.150 



30.100 



30.050 



30.000 



29.950 



29.900 



29.850 



29.800 

 and so on. 



Secondly find a line on the vernier which agrees exactly with a line 

 on the fixed scale (there will generally be one and only one such 

 line). Take its reading on the vernier, remembering that the 

 divisions run from below upwards 2, 4, 6, 8, 10 (marked i), 12, 14, 16, 

 1 8, 20 (marked 2), etc.,, and add this vernier reading to the fixed 

 scale reading. The sum will be the " barometer reading." 



