62 Proceedings of Royal Society of Edinburgh, [jan. 17 , 
cation of it with draught tube has yet been attempted. The 
screen consists of two distinct parts, — the lower, or screen proper, 
surrounding the bulb of the thermometer, is constructed to protect the 
thermometer from all radiation from below, while the upper part pro- 
tects the lower screen from the direct rays of the sun. The upper 
part consists of a square sunshade AA made of wood, and supported 
in a horizontal position at the proper height from the ground by 
means of four wooden supports LL attached to the corners, and fixed 
firmly in the ground. If the direct rays of the sun fell on AA it 
would get highly heated, and would heat the air on the under side 
of it, which might affect the readings of the thermometer. To pre- 
vent this, another piece of wood MM is placed over AA parallel to 
it, but with an air space between the two, to check the passage of 
heat downwards. The lower part of the screen consists of the three 
plates C, D, and E, fixed parallel to each other and to the lower 
side of the sunshade AA in the position shown. The plates are 
held in their places by long screw nails passing through the four 
corners. These plates may be made of any substance that is a non- 
conductor of heat ; wood is the only material yet tried. The bulb 
of the thermometer t is placed in the space between the two plates 
C and D, where it is protected from all radiation both from above 
and below, and to protect it from the horizontal radiation, it is 
surrounded by the annular piece E shaped in the manner shown. 
The stem of the thermometer t passes upwards through the sun- 
shade, and is protected by means of the louvred box 
When the screen was first used, the sunshade part consisted only 
of the two pieces AA and MM, but when the sun got very low in 
winter it w T as found to affect the correctness of the readings, and 
