Thus elastic force with dry bulb = 55° is ·433 in.} in the table. „ „ dew-point = 46°·5 is ·317 in.} ·317/·433 = ·73. If saturation = 100, relative humidity is 73. In Table VII. of Marriott’s _Hints_, a table is given which enables the relative humidity to be found by mere inspection. Thus if the dry bulb temperature is 58°·5, wet-bulb 51°·7, and the difference 6°·8, the relative humidity given in the table is 62. The =Rain-Gauge= is best made of copper in the shape of a circular funnel, usually 5 or 8 inches in diameter, leading into a bottle underneath. It must always be set in an open situation away from trees, walls, and buildings. According to Scott no object ought to subtend a greater angle with the horizon than 20° in any direction from the gauge. The rain is measured by pouring the contents of the bottle into a glass measure, which is graduated to represent tenths and hundredths of an inch on the area of the gauge, the measure holding half an inch of rain on this area. Snow is melted before being measured. [Illustration: FIG. 54. SNOWDON PATTERN RAIN-GAUGE. A. Copper Upper Part of Gauge. B. Funnel. C. Bottle. To the right is shown the glass measure inverted.] Observations of =wind= should include its direction and force. The direction is observed by means of a well-oiled and freely exposed vane. There are 32 points to the compass, but a reading to eight points suffices. The force of the wind should be estimated by Beaufort’s scale, from 0 to 12. Thus:— FORCE. MILES PER HOUR. 0. _Calm_ 3 1. _Light air_ 8 2. _Light breeze_ 13 3. _Gentle_ 18 4. _Moderate_ 23 5. _Fresh_ 28 6. _Strong_ 34 7. _Moderate gale_ 40 8. _Fresh_ 48 9. _Strong_ 56 10. _Whole_ 65 11. _Storm_ 57 12. _Hurricane_ 90 _Robinson’s anemometer_ is also employed, but it is not altogether trustworthy. =Sunshine= is recorded by the Campbell-Stokes burning recorder, and the Jordan photographic recorder. Of these the former is the more easily worked and gives more uniform results. It consists of a sphere of glass 4 inches in diameter, supported on a pedestal in a metal zodiacal frame (Fig. 55). The setting of the recorder should be due south, level from east to west, and with the axis of the ring inclined to the horizon at an angle equal to the latitude of the place, and so that the image of the sun, when the sun is due south, shall fall on the meridian line marked on the ring. The sun burns away or chars the surface of the cards inserted in the proper groove, and so gives a record of the duration of bright sunshine. [Illustration: FIG. 55. CAMPBELL-STOKES SUNSHINE RECORDER.]