Oct, lo, 1878] 



NATURE 



62 



is blowing from such direction as not to be within either 

 arc. 



Tbe length of time for which the wind has blown con- 

 tinuously from a rain direction or a dry direction is of 

 importance to be considered with other local signs and 

 indications. 



The pointer and scale (No. 5) on the right of and 

 below the barometer are called the dry-wind time-record, 

 and the pointer (No. 7) is called the "record-pointer,'" 

 and indicates, when set, the length of time the wind has 

 been blowing continuously from a "dry" direction, by 

 the figures showing the number of hours on the scale to 

 which it points. 



The pointer and scale (No. 4) on the left of and below 

 the barometer are called the rain-wind time-record, and 

 the record-pointer (No. 6) indicates, when set, the length 

 of time the wind has been blowing continuously from a 

 "rain" direction, by the figures showing the number of 

 hours on the scale to which it points. 



The record pointer on the rain- wind time-record (No. 6) 

 is always turned by the thumb-screw, and set pointing at 

 the figure o on the scale when the wind is not blowing in 

 the rain-wind direction. In the same way the " record- 

 pointer" on the dry-wind time-record (No. 7) is always 

 set pointing at the figure o when the wind is not blowing 

 in the dry direction. 



Wheti in actual use, the hour at which the witid-disc 

 pointer has been set is carefully noted. When the 

 weather case is next examined, the wind-vane is again 

 noticed, and the wind-disc pointer again examined or 

 adjusted. If it still continues to point at any part of the 

 same arc as before, the number of hours which have 

 elapsed since the last setting and during which the wind- 

 disc pointer has been so pointing is noticed, and the 

 record- pointer on either the rain-wind time-record or dry- 

 wind time-record is turned to show the number of hours 

 the wind has been thus noticed as blowing from the rain 

 direction or from the dry direction, as the case may be. 

 This proceeding is repeated every time the instrument is 

 set. It can thus be seen at a glance whether the wind is, 

 or not, blowing in a rain-wind or a dry-wind direction, 

 and for how long it has been so blowing. Whenever, on 

 noticing the wind-vane, it is seen that the wind has 

 shifted, the wind-disc pointer is set accordingly If it 

 now points at neither arc, or points to the different arc 

 from that at which it pointed at its last setting, the time- 

 record pointer on the rain-wind time-record or dry-wind 

 time-record (whichever may have been in use at the last 

 setting), is turned to point at the figure o (zero). 



The wind-disc pointer and the time-record pointer 

 ought to be set thrice daily at least, early in the morning, 

 at noon, and at sunset. 



The sunset disc (No. 12) consists of a circular disc, one 

 half of which is coloured red and one half of which is 

 coloured blue. The disc turns upon a central turning- 

 screw in such manner that half of the disc shows through 

 a semi-circular opening in the face of the weather-case. 

 The sunset-disc is set as follows : — At the exact time of 

 erery sunset the western sky and the character of the 

 sunset is carefully observed. The examination ought to 

 be minute and careful, lasting for about fifteen minutes. 

 If the sunset sky is clear or red, or markedly what is 

 known as a "fair weather sunsei" — a sunset such as is 

 generally held to indicate a clear or fair day to follow on 

 the next day, a day on which it will not rain — the sunset- 

 disc is turned by the turning screw until the semi-circular 

 opening shows all red. The sunset-disc, thus turned, is 

 described as set for a " fair weather sunset." 



If the sunset sky (the western) is cloudy or foul, or 

 markedly what is known as a "foul weather sunset," a 

 sunset such as is generally held to indicate foul weather 

 to follow on the next day — a day on which it will rain — 

 the sunset-disc is turned by the turning screw until the 

 semi-circular opening shows all blue. The sunset-disc 



thus turned, is described as set for a " foul weather sun- 

 set." If the appearance of the western sky and the 

 character of the sunset are neither markedly those of 

 a " fair weather sunset " or of a " foul weather sunset," 

 but such as to leave the observer in doubt how to style 

 it, the sunset-disc is turned to show half red and half 

 blue, or "doubtful." The sunset-disc, thus set, is 

 described as set for a " doubtful weather sunset." 



The term " fair weather sunset" expresses such con- 

 dition of the sky, particularly the western, and such 

 character of the sunset, as is considered to indicate a 

 fair day, a day on which it does not rain, for the day 

 ensuing. 



The term "foul weather sunset" indicates that the 

 appearances are such as to presage a rainy day, a day on 

 which rain falls, for the ensuing day. 



The term " doubtful weather sunset " indicates that 

 the conditions are such as to leave the mind of the ob- 

 server in doubt as to what the sunset presages for the 

 following day. Tlie indication is considered to be for 

 the period of time from the "sunset" of the day on 

 which the character of the sunset is examined until the 

 " sunset " of the following day. 



Dry- bulb and Wei-bulb Thermometers 



In the lower part of the weather case there are two 

 thermometers, a dry-bulb thermometer (No. 13) on the 

 left-hand side of the case, and a wet-bulb thermometer 

 (No. 14) on the right-hand side. 



The dry-bulb thermometer is like any other thermo- 

 meter, and shows by its readings the temperature of the 

 air. 



The wet-bulb thermometer is one, the bulb of which is 

 kept constantly moist by the water passing up from the 

 glass reservoir, through the wicking which covers the 

 thermometer bulb. 



The readings of the dry-bulb thermometer and those of 

 the wet-bulb thermometer, are more and more unlike, or 

 farther and farther ^' apart," as it is called, in proportion 

 as the air contains less and less moisture ; that is, is 

 becoming dryer. 



The readings of the dry-bulb thermometer and those 

 of the wet-bulb thermometer become more and more 

 alike — are nearer and nearer together — in proportion as 

 the air contains more and more moisture j that is, is 

 becoming saturated or li't-t. 



By the side of the dry-bulb thermometer (No. 13) is the 

 dry-bulb pointer which slides on the brass slide (No. 15). 

 By the side of the wet-bulb thermometer is the wet-bulb 

 pointer which slides on the brass slide (No. 16). In the 

 centre of the case is the "dry- and wet-bulb scale," 

 marked on the paper on which is the central brass slide- 

 bar (No. 19), and on this slide move the dry-bulb 

 keeper (No. 17) and the wet-bulb keeper (No. 18). To 

 set the thermometers examine first the dry-bulb thermo- 

 meter and move the "dry-bulb pointer" {So. 15) on the 

 slide until the outside point is exactly level with the top 

 of the mercury in the thermometer — as near to it as prac- 

 ticable. Examine next the wet-bulb .thermometer, and 

 move the wet-bulb pointer (No. 16) on the slide until the 

 outside pointer is exactly level with the top of the mercurv 

 in the wet-bulb thermometer, or as near to it as prac- 

 ticable, then turn to the "dry- and wet-bulb scale," and 

 on the " central brass slide-bar" (No. 19) move one of 

 the keepers until it touches, as nearly as possible — is on 

 an exact level with the inside pointer of the "drj'-bulb 

 pointer," then move the other keeper until it touches, as 

 nearly as practicable^s on an exact level with the inside 

 pointer of the " wet-bulb pointer." The thermometers 

 are now set, and the difference between their readings 

 can be known by counting on tbe "dry- and wet-bulb 

 scale " the number of degrees between the keepers. 



When the thermometers are examined and set again, 

 following the same plan, it will be easily seen whether the 



