H & S Timbers (Pty) Ltd has been the approved supplier of Stevenson Screens to the South African Weather Bureau and other research institutions since 1973.
Thomas Stevenson (1818-1887) - a civil engineer and father of the author Robert Louis Stevenson - is accredited with the design of the Stevenson Screen, which is still widely used today. He is also famous for inventing a new and much improved illumination system for lighthouses.
The screen is designed to protect the thermometers from the effects of direct radiation and precipitation, whilst allowing the free movement of air through the screen. The screens manufactured by H & S Timbers are constructed from kiln dried Eucalyptus Saligna finished with three coats of epoxy strontium chromate primer followed by two coats of white polyacrythane.
The front, back and side panels are double louvred with the outer louvre sloping downward and outward. The door has solid brass hinges at the base allowing it to hinge downward to the vertical position. When closed, the door can be locked using a solid brass hasp and staple. Three partially overlapping floorboards are fitted with the outer two sloping downward to allow rainwater to run off. Tool clips are fitted to allow easy fitting and removal of the thermometers. To offer maximum protection from the elements the screens are fitted with a white Glass Reinforced Plastic (GRP) roof.
Stevenson Screens are usually supported by means of a steel stand, which is firmly set in the ground. To comply with Meteorological Office Standards, the stand must elevate the screen, so that the bulbs of the Wet and Dry Bulb Thermometers are 1.25m above the ground. These stands are available in knocked down kit form.
H & S Timbers manufactures three sizes of Stevenson Screen as follows:
Ship
Screens
Usually used on research vessels and has an eye on the roof
so that it can be hung from a mounting hook. This allows the
screen to gimbal and remain in a vertical position at sea.
Manufactured to SAWB drawing 370 Design 2.
 |
 |
514mm
high x 310 mm wide x 180mm deep
|
|
_____________________________________________________________________________________________
Single Screens
Half-size screen used at automatic weather stations, and
manufactured to SAWB drawing 545 Design 1.
 |
 |
765mm high x 610mm wide x 593mm deep
|
|
_____________________________________________________________________________________________
Double Screens
Full-size screen manufactured to SAWB drawing 541 Design 4.
 |
 |
765mm high x 1050mm wide x 593mm deep
|
|