Accession No
6216
Brief Description
‘Hygrorule’ humidity slide rule, by Short and Mason, English 1924-1960
Origin
England; London
Maker
Short and Mason
Class
calculating; meteorology
Earliest Date
1924
Latest Date
1960
Inscription Date
Material
plastic; wood; organic (leather); metal
Dimensions
length 146mm; width 20mm; depth 5mm
Special Collection
Provenance
Inscription
“Short & Mason
London”
“PUT ARROW AT D.B.
READ R.H. AT W.B.”
“Made in England” [all on front of rule]
“Short & Mason Ltd.
London” [on the leather case]
Description Notes
‘Hygrorule’ humidity slide rule by Short and Mason, London; English; 1924-1960
Used to calculate relative humidity from readings of a psychrometer (wet and dry bulb thermometer). Designed to be more convenient than looking up the relevant data in hygrometric tables.
Slide rule has textured leather case with a springy metal rod inside to help hold its shape. Case is stamped ‘Short & Mason Ltd. London’ in gold. Accompanying page of instructions and explanation of use, quoted in full below:
“The No.3805 S. & M. Humidity Slide Rule combines simplicity with accuracy. It is used for ascertaining relative humidity from wet and dry bulb thermometer readings and obviates the necessity for reference to tables. Convenient in size, and protected by a strong leather case, it can be carried in the pocket and is therefore readily available at all times. The rule is made of white plastic and is mounted on a wood back, with bold figures and graduations. Two scales are provided, on the reversible slide, one for screen and the other for aspirated thermometers. The main advantages are:
(1) One setting only is required
(2) Can be set to a fraction is required
(3) Accuracy at any point is within ±1% of readings furnished by tables
(4) Cumbersome tables are unnecessary.
INSTRUCTIONS FOR OPERATING
As mentioned above, the slide is reversible. One side is marked in black with the identification “Sling/Assman.” This is used with aspirated or Whirling type hygrometers. The curves have been plotted according to Psyschrometric Tables by C.F. Marvin, published in the USA.
On the reverse side, the figures and graduations are marked in red, and these are to be used with hygrometers installed in screens or on walls, or where there is little air movement. The curves have been plotted according to the Hygrometric Tables issued by the British Meteorological Office, Form M.O. 265.
To obtain relative humidity, the arrow on the slide should be set to the dry bulb temperature on the lower scale. The relative humidity is read against the upper scale at the wet bulb temperature. For example, referring to the illustration, it will be seen that the dry bulb is 65°F. With the wet bulb at 54.5°F, the relative humidity is 50 per cent.”
References
Events
Description
This slide rule was used to calculate relative humidity from readings of a psychrometer (wet and dry bulb thermometer). Relative humidity is a measure of the amount of water vapour present in the air.
This slide rule was made between 1924 and 1960 by Short & Mason, who were British manufacturers of meteorological instruments. (Short & Mason acquired by Taylor Scientific Instruments in the early 1900s but continued to manufacture under their name.) The humidity slide rule was designed to be more convenient than looking up the relevant data in books of tables. A sheet accompanying the instrument gives instructions for its use:
“The No.3805 S. & M. Humidity Slide Rule combines simplicity with accuracy. It is used for ascertaining relative humidity from wet and dry bulb thermometer readings and obviates the necessity for reference to tables. Convenient in size, and protected by a strong leather case, it can be carried in the pocket and is therefore readily available at all times. The rule is made of white plastic and is mounted on a wood back, with bold figures and graduations. Two scales are provided, on the reversible slide, one for screen and the other for aspirated thermometers. The main advantages are:
(1) One setting only is required
(2) Can be set to a fraction is required
(3) Accuracy at any point is within ±1% of readings furnished by tables
(4) Cumbersome tables are unnecessary.
INSTRUCTIONS FOR OPERATING
As mentioned above, the slide is reversible. One side is marked in black with the identification “Sling/Assman.” This is used with aspirated or Whirling type hygrometers. The curves have been plotted according to Psyschrometric Tables by C.F. Marvin, published in the USA.
On the reverse side, the figures and graduations are marked in red, and these are to be used with hygrometers installed in screens or on walls, or where there is little air movement. The curves have been plotted according to the Hygrometric Tables issued by the British Meteorological Office, Form M.O. 265.
To obtain relative humidity, the arrow on the slide should be set to the dry bulb temperature on the lower scale. The relative humidity is read against the upper scale at the wet bulb temperature. For example, referring to the illustration, it will be seen that the dry bulb is 65°F. With the wet bulb at 54.5°F, the relative humidity is 50 per cent.”
07/05/2008
Created by: Ruth Horry on 07/05/2008
FM:46688
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