216 



TENTH ANNUAL REPORT OV 



of "board, (B E,) placed at least fifteen or twenty inches above tlie in- 

 strument. The lower part, (J J,) or the basis, may remain open. 



n Fig. 1. o' 



View from the outside. 



Fig. 2. 



[The foregoing is a convenient arrangement by which the observa- 

 tions can be taken without exposing the observer to the weather. To 

 insure greater accuracy the windows during the intervals of observa- 

 tions may be closed with a wooden shutter. The outside of the lat- 

 tice work should be painted white, to reflect off the light and heat 

 which may fall upon it.] 



Tha thermometer must be placed exactly perpendicular, 

 the middle of the scale being at the height of the eye against 

 the two small wooden bars^ so that the top of the scale being 

 fixed by a screw to the upper bar^ the bulb may pass at least 

 two or three inches beyond the lower bar. The instrument 

 Ijjujj. is attached to the last by a little metallic clasp. (Fig. 2.) 

 It will thus be placed ten or twelve inches from the panes, 

 from the screen, and the other parts of the window. 



[In a later arrangement, a single transverse bar is used. 

 This being placed at the necessary height, the thermometers 

 are attached to it by small metal brackets, which support 

 them at a distance from the bar of about two inches. The 

 metal brackets are permanently screwed to the bar, and the 

 thermometers are fastened to them by small finger-screws, 

 by which they can be detached at pleasure. The order of placing 

 them is shown in the cut.] 



Heading. — To read the thermometer, the eye must be placed exact- 

 ly at the same height as the column of mercury. Unless this precau- 

 tion is taken, there is a liability to errors, the greater in proportion 

 to the thickness of the glass of the stem and the shortness of the de- 



[LI 



EH©' 



